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Re: AGM & GEL BATTERY INFO for POWERCHAIRS

Postby Burgerman » 15 Sep 2017, 02:25

Yes but they no longer offer us 20 percent VAT off. Thats about £50 lower per battery!
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Re: AGM & GEL BATTERY INFO for POWERCHAIRS

Postby Burgerman » 15 Sep 2017, 02:46

The other thing is this.

Lets say you pay 250 each = £500.
You could pay $1000 for a lithium battery instead.

Lets compare the two deals.
Lead will give you 68Ah and around 40 of that is actually usable. Giving you say 15 miles range (initially), falling to 10 after say 18 months and then you replace.
So 500 div by 18 months = £27.77 per month for an average of 12.5m range.

Lithium, for £1000 gives you 120Ah of which ALL is usable. Instead of 15 miles range you now have 45 miles. 3x better!
Instead of the odyssey 400 cycles (18 months or less charged nightly) you get either 10s of thousands of cycles if you only go 15 miles. And you can charge every 2 days and yet still only use 66% discharge level. So get at least 8k charges. Thats probably going to outlive that chair, (and you). So we say a nominal 10 years plus for easy numbers.
So with lithium, you get 3x the range, all for less than one third the cost at £8.30 per month...

The realty is even better. Because even if you lost HALF the range, at say 15 years, thats still got much more than a set of brand new lead bricks! So if this is OK, then you probably keep going and its down to around £5.80 per month. ;)

Nobody can afford lead. It performs crap. And works out 3 to 5 times more expensive with rubbish range!
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Re: AGM & GEL BATTERY INFO for POWERCHAIRS

Postby SWalkusz » 15 Sep 2017, 04:49

Burgerman wrote:The other thing is this.

Lets say you pay 250 each = £500.
You could pay $1000 for a lithium battery instead.

Lets compare the two deals.
Lead will give you 68Ah and around 40 of that is actually usable. Giving you say 15 miles range (initially), falling to 10 after say 18 months and then you replace.
So 500 div by 18 months = £27.77 per month for an average of 12.5m range.

Lithium, for £1000 gives you 120Ah of which ALL is usable. Instead of 15 miles range you now have 45 miles. 3x better!
Instead of the odyssey 400 cycles (18 months or less charged nightly) you get either 10s of thousands of cycles if you only go 15 miles. And you can charge every 2 days and yet still only use 66% discharge level. So get at least 8k charges. Thats probably going to outlive that chair, (and you). So we say a nominal 10 years plus for easy numbers.
So with lithium, you get 3x the range, all for less than one third the cost at £8.30 per month...

The realty is even better. Because even if you lost HALF the range, at say 15 years, thats still got much more than a set of brand new lead bricks! So if this is OK, then you probably keep going and its down to around £5.80 per month. ;)

Nobody can afford lead. It performs crap. And works out 3 to 5 times more expensive with rubbish range!

All I can find ready made is
http://www.rothervalleyoptics.co.uk/BP2564.html
https://www.amazon.co.uk/LiFePO4-LITHIU ... B01BDPZ9F6
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Re: AGM & GEL BATTERY INFO for POWERCHAIRS

Postby Burgerman » 15 Sep 2017, 09:14

All those have the exact same issues as all the ready to go bricks. And are a waste of money.

Except the headway one that is too small Ah, and we are already doint those better here without the daft BMS issues, and with 90 to 120Ah! For a lot less £££. All they have done is copied what we do on here for nearly a decade, but made a smaller one. And instead of charging properly are relying on the typical BMS which is the source of all the lithium problems and shorter lifespan. And added their markup. You can do that yourself cheaper by ordering from say www.evassemble.com.

Theres are many lithium conversions, ready to go swap bricks that will "work". Thats easy. But finding one thats reliable, that will give the real benefits that lithium offers is not. None of these ready to fit BMS equiped smaller sized ones will do this. You are throwing money at something that at best will only give marginal range improvement and not last as long as it should and may be unreliable and cause problems. This is of course your choice. But I have looked at all this before. And thats why I dont use any of those options!

Read the lithium thread here, because you are going over all the stuff already discussed to death for years!
viewtopic.php?f=2&t=1813
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Re: AGM & GEL BATTERY INFO for POWERCHAIRS

Postby SWalkusz » 17 Sep 2017, 11:59

Sonnenschein/Dryfit (German) and Deka Gel-Tech (US)

Charging.Sonnenschein/Dryfit (German) A200 product is correctly charged (@ 2.4v/cell)14.4v/ and float voltage is (2.3v/cell)13.8v) @ 20°C to 30°C. US (Deka Gel-tech) is correctly charged at (2.35v/cell)14.1v with (2.3v/cell) 13.8v float @ (68°F) 20°C.
For lower and higher temperatures, from (minus) -22ºF up to (plus) +120ºF, charge voltages should be adjusted according to the graph supplied with each battery. (A 500.)
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Re: AGM & GEL BATTERY INFO for POWERCHAIRS

Postby SWalkusz » 17 Sep 2017, 12:37

The Sonnenschein GF-Y Exide technologies (A-500) are Euro standard charging 14.4V (10-30 degrees C)
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Re: AGM & GEL BATTERY INFO for POWERCHAIRS

Postby Burgerman » 17 Sep 2017, 13:44

True. Some newer sonnenschein claim to use a different mix of pasted material that is more tolerant and may not damage gel at 14.4V. (gasses at higher voltage). But be careful because battery manufacturers claim this to allow a battery to comply with a standardised harge system, and so sell more too. So it may be a marketing change only! Plus its not possible for one voltage to cover a 10 to 30 degrees range! Its just sell sheet marketing.

So are MK sold as 14.4V compatible. You can, it will work, its compliant, and its safe (ish).

But that isnt the full story. They CAN be charged at 14.4V. (or 15V!) Provided you dont care about losing approx half the cycle life. At £500 a set I would think it matters. MK and Sonnenschein are exactly the same. Sonnenschein developed the system of starved gelled electrolyte, and exact pasted lead dioxide chemical paste mix/grid etc. They licenced it to MK who are a bigger manufacturer in the US. Both are identical in tech details originally.


The CORRECT voltage for max cycle life in both cases (13.80 to 14.1MAX at 20C) So idealised 13.95V.

All of that info is available on the tech sheets from both Sonnenschein and MK. I no longer have the sonnenchein data online, but retained the MK ones here. I have the others on my PC.

Heres the MK tech charge data sheet.
http://www.wheelchairdriver.com/MK1.pdf ACTUAL MK CHARGE DATA IF YOU CAN FIND ANY CHARGER TO DO THIS.

http://www.wheelchairdriver.com/MK2.pdf AGM and Gel compared, tech data. Note the CHART D showing 60% loss of cycles at 0.7V too high charge voltage. And 22% loss at just .4v too high...
Also note correct charge voltage for gel at 20C. And then remember that after use on a 30C day the battery may be 35C so the correct charge voltage is much lower than this still! See: Gel Charge and Float Voltages at Various Temperature Ranges, on page 11.

http://www.wheelchairdriver.com/MK2.pdf Note charge voltage MAXIMUM and warranty void if ignored... On these three.
http://www.wheelchairdriver.com/MK2.pdf
http://www.wheelchairdriver.com/MK2.pdf
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Re: AGM & GEL BATTERY INFO for POWERCHAIRS

Postby Burgerman » 17 Sep 2017, 14:06

I am not sure that I would charge the Sonnenschein at 14.4 though. If you try that, the current never drops to the 1000thC point, and in fact begins to rise again. A sign of thermal runaway. At least on an older set I have here. So while it may be compliant, I am not sure its wise. If you charge at 14.1 they end charge normally.
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Re: AGM & GEL BATTERY INFO for POWERCHAIRS

Postby Fedor » 18 Sep 2017, 23:01

Hello again. The story with balalaikas, bears, vodka and good GEL batteries ended successfully. I took MK Powered (yes, I know it's shit and I'm in the process of switching to lithium). Here's the datasheet: http://www.mkbattery.com/images/M24SLDGFT.pdf

I read the technical manual from the MK, but I still have a question. I have a charger that can charge the battery with two profiles: IUI or IUU. Which one is better for GEL?

Thank you all again.
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Re: AGM & GEL BATTERY INFO for POWERCHAIRS

Postby Burgerman » 18 Sep 2017, 23:16

You can use IU, with low termination and long time limit, IUI with accelerated finish but its hard to get right, IUU which is ok but in cyclic use not strictly required as long as you terminate the CV stage at a low current, IUUU for long term storage. And the devil is in the details which matter.

In an ideal world you would use IU only if you get it RIGHT!:
Constant Current (of approx 1/4 the battery capacity) to 14.0 to 14.1V maximum at 20 degreesC.
Hold it at 14.1v until charge current drops to approx 500thC (old battery) to 1000thC where C is capacity. Or approx 8 to 12 hours limit whichever is sooner. At which point its 99.95% charged and can be used.
Add this:
Followed by 13.6V CV up to around a day, to add that 0.05% missing occasionally, falling to 13.3V for really long term storage to prevent discharge. And you have your IUU(U)

Most chargers end CV (IU) too soon, at around 100thC, or .7A, and so REQUIRE a float stage (CV at lower voltage) to complete charge afterwards or the battery sulfates . (Hence the 500th to 1000thC termination point above with time limit). So then a IUU becomes essential.

Remembering that CV over 14.1v at room temp, shortens service life so generic 14.4v chargers will cost you around 40% of the cycle life.

If you cannot do this, because a full charge takes too long you can follow the accelerated charge system here (IUI):
http://www.wheelchairdriver.com/MK1.pdf But that is very complex to get right, so depends on knowing the discharge level and a very programmable charger like the PL8 that I use. Even then its not ideal.

Your data sheet is a sell sheet. They say you CAN charge at 14.6 volts. And you can. They dont tell you the affect on service life!
Heres the actual data sheet:
http://www.wheelchairdriver.com/MK2.pdf Covers gel and AGM MKs. Chart D.
Note the CORRECT charge voltage if you value service life is 13.8 to 14.1 at 20C. And theres a very clear chart showing these things.

Also note charging comments here:
http://www.wheelchairdriver.com/MK3.pdf
http://www.wheelchairdriver.com/MK4.pdf
http://www.wheelchairdriver.com/MK5.pdf
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Re: AGM & GEL BATTERY INFO for POWERCHAIRS

Postby Burgerman » 18 Sep 2017, 23:41

Did that help?
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Re: AGM & GEL BATTERY INFO for POWERCHAIRS

Postby Fedor » 19 Sep 2017, 12:21

Burgerman wrote:Did that help?


Yes, very useful and constructive.Thanks you!
In many other documents on this subject a lot of marketing shit or inaccurate information.
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Re: AGM & GEL BATTERY INFO for POWERCHAIRS

Postby Burgerman » 19 Sep 2017, 14:09

MK and other gel manufacturers realised that after 2 decades of giving the right accurate info, that nobody listens, and that gel batteries were about 2% of the total wet, sealed, AGM dominated market. And almost every charger ignored their needs and charged all sealed batteries at the same universal 14.4 to 14.6V. So at best it caused confusion, at worst it cost them sales as solar setups, boats, and powerchairs all had generic chargers.

So they quietly withdrew the real tech info, and older sell sheets, with good info, and started with the new 13.8 to 14.6 glossy sell sheets. Its not that the info is wrong. Its not. You can charge at 14.6V if you want. Its just that all the detailed cycle life info became very scarce! So they prefer to allow users to sacrifice service life in the interest of sales. You just need to see throught the smoke and mirrors.

The problem is this. As soon as any lead/sulphuric acid/water battery becomes close to fully charged, and at a specific voltage of around 14v at 20C it begins to produce hydrogen and oxygen gas as it then breaks down the water in the electrolyte/gel. The higher the voltage above this point the more gas it produces. All sealed batteries are whats called recombinent. It just means that they can turn this gas back to water at low rates (low currents) at the acid/plate interface. If this current is exceeded (by increasing voltage), then the recombination rate is exceeded. Then bubbles are produced and these then pressurise the battery. Which are sealed but have a pressure relief valve. (Do it a lot at say 15v and water is lost for good). Otherwise no damage. Except with the gelled electrolyte (silica gel added to make a heavy paste). In this case these bubbles cause loss of contact with the plates, shrinkage and drying of gel, and as it dries it out causing cracks over time. This decreases capacity and increased internal resistance. So a gel battery cant stand the same charge voltage as an AGM type or wet battery.
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Re: AGM & GEL BATTERY INFO for POWERCHAIRS

Postby Dan » 19 Sep 2017, 14:44

On the PL8 (MK Gel 12A XLR ONLY!!! 73Ah) preset the charge voltage is set to 2.350. I guess that is per cell, 2.350 x 6 = 14.1

My house is always quite warm, about 24C. Would it be best to drop the charge voltage a little? I also changed to charge amps from 12A to 10A to be extra safe.
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Re: AGM & GEL BATTERY INFO for POWERCHAIRS

Postby Burgerman » 19 Sep 2017, 15:11

12A is OK. 10 works too...

You could lower it to 14V (27.97v) if its really always warmer than 20C. By swapping to 2.330v.
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Re: AGM & GEL BATTERY INFO for POWERCHAIRS

Postby Fedor » 19 Sep 2017, 17:53

Burgerman wrote:12A is OK. 10 works too...


What about 8A or 6A? It is clear that this requires more time. How much does the charging current affect the Gel's battery life?
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Re: AGM & GEL BATTERY INFO for POWERCHAIRS

Postby Burgerman » 19 Sep 2017, 18:33

Its about time. And no I am not stating the obvious!

If you charge a battery at 100A it still takes almost as long to charge as it does at say 30A. Why?
Because after the initial bulk of the charge at MAX amps, the current falls away naturally in 15 mins to a lower level and the voltage stays the same. So it will still take around 10 hours to charge the above FULLY in both cases, give or take half an hour. (Although you can put more back fast initially, as a top up during the day, as I do regularly with a 40A power supply).

But if you charge at say 2A and you have a fully discharged 70Ah battery it will sit at CC and 2A for around 35 hours, and then spend another 5 or 6 hours at CV topping up... Almost 2 days.

What I am trying to say is that more than say 25 to 30A isnt worth it. But less than this doesent really leave adequate time over an 8 hour night to get a complete charge if the battery is heavily discharged.

So in an ideal world, for cyclic use you would aim for MKs recomended rate, http://www.wheelchairdriver.com/MK1.pdf of 30%of rated capacity so on a 73ah battery like the ones we use thats 22 Amps. But the actual figure isnt critical.

It gives us the greatest chance of a complete fully saturated charge in the 8 hour night we have available. More amps doesent achieve much, but less means inadequate time available for the charge to complete.

Think of this. A 73Ah MK at 8A will if fully discharged take over 9 hours to reach CV, and another 5 or 6 hours for the CV voltage current to drop to say 73mA (1000thC) before its full... And we have 8 hours?

I know mobility chargers will say DONE inside this 8 hour period, but they lie. They are still charging after you get the green, in many cases. And where they are not your battery isnt actually full. Meaning it will sulfate over time. It takes around 12 to 16 hours to FULLY charge a gel battery. Unless you use a PL8 and set a long CV with low termination point.
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Re: AGM & GEL BATTERY INFO for POWERCHAIRS

Postby Burgerman » 19 Sep 2017, 19:05

Summary!

Charging at different rates does not change service life as such at all. It doesent hurt the battery. If you dont achieve full saturation, a 100% complete charge then THAT does.

So charging faster in a limited 8 hour night, actually prolongs battery life by getting the bulk done fast, allowing much longer to finish. In affect it reaches CV sooner allowing a more complete charge overnight.

On a group 24MK. Less than the recommended 22A is worse (less time for CV to end). More than 22A achieves very little overall.

12A RMS is as high as the plugs/connectors/bus cables allow safely on a powerchair. So thats why that profile was set to 12A.
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Re: AGM & GEL BATTERY INFO for POWERCHAIRS

Postby Fedor » 20 Sep 2017, 15:49

Thanks for the detailed answer. Rarely where you can find such compact and accurate information. Thank you.

About charge voltage and commercial Gel chargers. It's ridiculously comical, but when I contacted a developer of one of these and asked what profile they use and what they recommend voltage for the MK batteries. I told them about the recommended voltage not more than 14.1v and gave them a link to MK2.pdf.

They contacted the engineer from MK Powered and he said that 14.4v (28.8v) the best for such batteries. And 28.2v is not a fully charged battery. So, MK Powered has an extensive documentation with a lot of examples, but their engineers do not follow it.

It's like a conspiracy.

On the one hand, we can blame the developers of chargers. On the other hand, they follow the advice of battery developers.
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Re: AGM & GEL BATTERY INFO for POWERCHAIRS

Postby Burgerman » 20 Sep 2017, 16:54

It depends on if you speak to all those employees that have been told that 14.4 is "ok", or some dummy that has just read the latest mobility sell sheet as this is the new marketing line. Or if you go by the once freely available mass of MK technical documents. Two years ago, they all quietly disappeared from MKs web sites. To be replaced by, nothing! Ignorance allows them to sell more batteries!
There is now no tech sheets available at all. Just glossy (newer) dumbed down sell sheets remain, with a now wider voltage limit allowed. Non of the original ones that mention 14.1v max or show the affect on cycle life etc, or warranty void etc remain. We know the truth. Its why I keep hold of the tech sheets here. The reason they do it, is it allows them to sell batteries that conform to the "standard" 14.4V IUoU EU charger profile. A universal standard that is safe for all lead based batteries. But safe is a different thing to optimal. Sonnenschein did something very similar, but instead of smooth natural voltage/temp curves as expected on the graphs, they just DREW some straight lines that happen to comply!

Theres another problem with charging at 14.4v. And I can show you it happen easily. With MK and Sonnenschein gel. And that is that if you have an older battery, or a newer one on a warm day, it will never drop down to the low current point where the charger is looking to terminate. Because the gassing 14.4V causes, makes heat. Which warms the battery. (which is why you need to watch it, or set a safe 8 hour time limit to try and catch it. And instead of current falling it starts to climb again. Current rises. Which warms the battery. Which causes current to rise more. Rinse and repeat. You end up with a bad smelling melted battery - its called thermal runaway.
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Re: AGM & GEL BATTERY INFO for POWERCHAIRS

Postby Fedor » 11 Oct 2017, 04:05

Thanks again.

I have another small question about the GEL. Do all models and manufacturers have the same discharge curve or can it change? At me on absolutely new MK Powered (i previously used a different brand) the display of a charge on a wheelchair concerning a distance of travel has changed, and for the worse.

I now test and investigate possible causes (measuring the voltage in different stages), but can this be the error indicator of the discharge on the wheelchair? If, of course, the discharge curve could change...
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Re: AGM & GEL BATTERY INFO for POWERCHAIRS

Postby Burgerman » 11 Oct 2017, 04:29

Different battery TYPES such as Gel, are all basically the same. Although different to AGM, or wet, or pure lead like odyssey/optima etc. But all are pretty close.

But heres the thing. The battery gauge is worse than useless. It works on voltage, averaged over time.

If I take a brand new MK battery, and drive a chair for 5 mins hard, say up a steep hill, it may use only 2 or 3Ah, and yet its voltage will fall a long way. A battery meter will then read a lot lower than its true state of charge for 12 to 24 hours.

Likewise, if I drive along a flat road at constant speed at say 3mph, current draw is low, but intime I once again I have taken the SAME 3Ah out of the battery more slowly, the battery gauge will now still read full. Because the voltage will not have dropped much.

Now some batteries do this more than others. The lower the peukert value, and the lower the internal resistance the less the voltage drops under a heavy load, and the sooner it recovers. And to complicate things further, a battery resistance, and peukert values go up as you discharge it. Som, likethe MK, do this a LOT on purpose. It means that they get a better cyce life due to the battery running out of electrolyte before the plates become fully sulfated as you discharge. In other words they use whats called starved electrolyte. As they become discharged, the sulfuric acid becomes weaker. It turns into lead sulfate and lead dioxide and coats the plates. Eventually the battery electrolyte is basically just water which doesent conduct. So as you try to drive the voltage colapses. And protects the plates. Other batteries such as the Odyssey ones, are not starved, so you can discharge them much deeper at high loads with less voltage collapse, and faster recovery.

What does all this tell us? Stick some tape over the battery gauge and ignore it. Its only there to make you feel good. It cant ever know the state of charge. And neither can you with a volt meter.

Theres 3 ways to know the state of charge of a sealed lead battery. And ONLY three.
1.Fully charge it, at the correct voltage, till its dropped below 1000th of capacity in Amps. So 70mA for a 70Ah battery. Then its 100 percent!

2. Fully discharge it to around 10.8V over 24 hours or longer at low current and then its at 0% charge.

3. DISCONNECT it completely from the powerchair. Wait 24 hours. Not sooner. Then measure voltage with a recently calibrated quality voltmeter. Then look at the temperature of the battery. Then compare this to the state of charge/temperature graph from the specific battery manufacturer.

Thats the only way. Everything else is a bad guess.
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Re: AGM & GEL BATTERY INFO for POWERCHAIRS

Postby Fedor » 11 Oct 2017, 17:29

I understand that it is more correct to look at the actual voltage of the battery with a considerable pause after the load current or charging.

I just was confused that if the discharge curve is the same, then why did the behavior of the battery gauge change?
But logically, I understand that this can have many reasons. And yet not the fact that the problem is in the battery itself.

Now my indicator shows 5 units (total 7). And the batteries show 12.75v on both after pause.
I found updated technical documentation for the MK Gel batteries here: http://www.mkbattery.com/pdf/mktechm.pdf

It is curious, but in comparison with the old documentation (MK2.pdf on this site) there the data on the discharge voltage changed. This is the latest documentation and I have no idea why it has changed:

Image

Well, if I take this data, then 12.75v is something like 87% of the charge and battery gauge on the wheelchair is exactly lying. But I will continue to measure the battery gauge and the real voltage after a pause. I want to understand exactly how the battery behaves. At the same time, I do not want to very deeply discharge and shorten the life of the battery. So this is important information i think.
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Re: AGM & GEL BATTERY INFO for POWERCHAIRS

Postby Burgerman » 11 Oct 2017, 17:47

Well, if I take this data, then 12.75v is something like 87% of the charge and battery gauge on the wheelchair is exactly lying.
They ALL lie!
But I will continue to measure the battery gauge and the real voltage after a pause.

Your pause better include a day, and the battery discharge history in Amps over time, battery temp, battery age and cycle life, and remaining capacity too, or no amount of examination can tell you anything useful!
I want to understand exactly how the battery behaves. At the same time, I do not want to very deeply discharge and shorten the life of the battery. So this is important information i think.

To determine state of charge, on a new HEALTHY battery with full Ah capacity available, which is only the first few months of use, you need a Turnigy Watt Meter. It counts Ah out. Or in on charge. And its cheap.Voltage wont help you.
However that too is problematic. Because at what point do you decide a 73Ah is say 80% discharged? You cant ever reach that point on a lead battery./ powerchair because it stops moving after around 50Ah at best! So a batteryu meter showing a true 20 percent remaining will allow you to break down at about the 66% point!

No its a waste of time. I can charge 2 batteries to 100 percent. I can then take 10Ah from each one. In a different way.
Lets say I take .5A for 20 hours from one.
And I take 500A from the other say cranking my van for 50 secs.

BOTH batteries are now at the exact same state of charge.
Batt A is still sitting at 12.85 approx, and will climb very slightly by .1 of a volt over the next 24 hours.
Batt B is now down to well below 10V and its voltage initially climbs fairly fast, and you will be able to watch it do this right up to ALMOST the same 12.85V eventually. But it will take at least 24 hours.

And the actual level it drops to has many variables... Even temperature, acid starting strength, acid volume, and battery peukert value and internal resistance all vary between different batteries - even of the same type/make but different case sizes.

The batter gauge, and terminal voltage/state of charge is pretty much pointless. UNLESS you wait a full day.
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Re: AGM & GEL BATTERY INFO for POWERCHAIRS

Postby Burgerman » 11 Oct 2017, 18:03

Remember here that 2C is 140Amps. And we need that to turn... And it only goes to 2 and a bit!


Image

Discharge voltages of a typical group 24 tubular low impedance deep cycle battery like an odyssey. An MK gel shows a worse performance than this at high discharge currents. Remember that we need nearly 200A to cross a threshold or turn iun place on a nose heavy rear drive chair for eg.

Remember that your chair wont move if it sees less than 18V typically.

Heres the same thing for a lithium cell... To follow.
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Re: AGM & GEL BATTERY INFO for POWERCHAIRS

Postby Burgerman » 11 Oct 2017, 18:15

With lithium it doesent matter much what rate you discharge them. They give much the same Ah (the full rated or greater regardless.

This is a 100Ah lithium ion phosphate graph from victron energy.

.5C is 50A discharge, compare to the lead above!!!
Remember that 2C is 200A.
3C is 300A
5C is 500A discharge...

Image
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Re: AGM & GEL BATTERY INFO for POWERCHAIRS

Postby Fedor » 11 Oct 2017, 20:19

I am well aware of the benefits of lithium and plan a complete transition to them.
But at the moment I'm using the new MK Gel and trying to figure out what they're capable of.

Before that, I also used Gel, but from Eternity Technologies, it's a marketing datasheet: http://www.eternitytechnologies.com/wp- ... 04-web.pdf
I was not surprised that battery gauge is lying, but that it has changed from replacing the Gel of one brand, to the Gel of another brand (same capacity). This in my opinion is strange. I have another 3 months to return them under warranty, but for now I'm trying to figure out why this happened and whether I have the same capacity as before or not.

Remember that we need nearly 200A to cross a threshold or turn iun place on a nose heavy rear drive chair for eg.


I saw your video with measurements of current consumption when turning on a carpet, grass, and the like. But I now have a stock controller with 50A and bursts of about 75A, there's also a fuse between the batteries, which is definitely less than 100A. So, if I understand correctly, with this configuration, there's nowhere to take 200A. This is a technical limitation (and it's shit).

I understand that there are a lot of factors when using batteries. But in my case I just replaced the two Gel batteries (Eternity), on the other two Gel batteries (MK Powered).
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Re: AGM & GEL BATTERY INFO for POWERCHAIRS

Postby Burgerman » 11 Oct 2017, 20:33

Most powerchairs use a fuse that is considerably lower than the current that it passes. A fuse isnt a thing that pops as soon as it sees its rated current. A 50A fuse will take 150A pulses, 100A for short periods, and its rated value plus a little all day long. Your controller can demand 75 plus 75A from your battery. So you will get periodic demands for 150A.

I was not surprised that battery gauge is lying, but that it has changed from replacing the Gel of one brand, to the Gel of another brand. This in my opinion is strange. I have another 3 months to return them under warranty, but for now I'm trying to figure out why this happened and whether I have the same capacity as before or not.


This is what I am trying to explain to you. Its in no way strange. The batteries were a different make. They will be a different impedance, and different level of peukert to the previous ones. So the voltage depression caused by any given load mad be greater, and you may get less actual capacity from a perfectly healthy battery of the same or GREATER Ah capacity as the original.

I posted that chart comparison to show that the lead battery voltage and capacity drops away horendously under load. And every make varies. Theres only 2 batteries worth fitting in a powerchair, and those are both very low impedance for their cycle life capability.
The Odyssey is 68Ah battery for eg 2.5mOhm, and so suffers HALF the voltage drop under any given load, and the voltage recovers at twice the speed, compared to say the 73Ah MK. But its terminal voltage at a full charge is lower. So the gauge reads lower drom the start, sags less in the middle, and then the smaller batter will take you FURTHER as its resistance doesent increase with discharge level to the extent that the MK does.

Your gel batteries may well vary in the same way. I cant say because no spec sheet.
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