New Mk batteries for my C300 question

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New Mk batteries for my C300 question

Postby DirtinLa » 12 May 2021, 20:11

Just got these in and am wondering if my factory charger is sufficient

They came in at 13.0 both exact and I have topped them off and now ready to install.

On charger 14.4. Off charger 13.9

Suggestions please?
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Re: New Mk batteries for my C300 question

Postby Burgerman » 12 May 2021, 20:49

2 things kill off MK gel (and all gel) batteries.

1. Charging at the AGM battery charge voltage of 14.4V. The CORRECT charge voltage is 13.8 to 14.1V maximum. At 20C or 68F. Aim for the higher 14.1V but not more! As it helps charge faster in the limited time we have available. If the temp is warmer, in suller drop to 13.9V at around 30C. So your charger is damaging the battery.

2. Charging for insufficient time. It takes TWENTY hours to FULLY charge a lead battery. Or more. If your charger is a modern 3 stage one, it will likely start at max 8A which is lower than ideal, and the voltage will rise slowly to 14.1V per batt. This takes hours - 1 hour for every 8Ah you used up during the day. It should then reach and stay at 14.1V for approx 8 to 12 hours. At this point its 99% charged. Current will have dropped to a very low 0.1A approx level. And the battery will now drop to a lower 13.6V float. This takes it from 99% charged to 100% over a couple of days.

Is it important to fully 100% charge? Yes. The battery coats the plates, including inside the plate active material with lead sulfate as it s discharged. When you charge the battery it returns this back into the electrolyte. If you dont complete the charge some traces remain. Over time this turns to larger non conductive crystals. And then they cant ever be removed. Do this undercharging every day and your battery capacity decreases, along with range. And eventually you throw it away.

This is what the mobility industry think is OK! Because they sell you a cheap useless charger and you get to buy more batteries. They dont care or even know.

So. next question!
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Re: New Mk batteries for my C300 question

Postby Burgerman » 12 May 2021, 20:52

Note that the CORRECT voltage here is the centre point of 13.8 to 14.1V. So 13.95V is what they are talking about.

Look what a few mV too much does to your cycle life. You are charging at 14.40V instead of 13.95V. So 0.45V above "recommended" voltage.
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Re: New Mk batteries for my C300 question

Postby Burgerman » 12 May 2021, 20:57

Here is the recommended Voltage, Vs the temperature. For GEL batteries.

And a 3 stage profile. The recommended voltage should be at CV or ABSORPTION for 8 to 12 hours.
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Re: New Mk batteries for my C300 question

Postby DirtinLa » 12 May 2021, 21:18

do you suggest using the permobil charger or should i purchase another if so which one?
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Re: New Mk batteries for my C300 question

Postby Burgerman » 12 May 2021, 21:27

I dont know what it does.
If it charges at say 8 to 12A, until it reaches 14.1V, and then stays at 14.1V for at least 8 to 12 hours after a typical days use, and then falls to 13.5 to 13.6V after this, then use it! Double these numbers for a 24V system obviously.

If it doesent do that, it will still work, but it will be giving you a much shorter service life, cycle life etc.

Theres few chargers that do it correctly. And all those that do require YOU to configure and understand what you are doing. It all depends how much you care!

Heres what MK say you should do:


http://www.wheelchairdriver.com/MK1.pdf
http://www.wheelchairdriver.com/MK0.pdf
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Re: New Mk batteries for my C300 question

Postby Burgerman » 12 May 2021, 21:44

What do I use?

Well that depends...

Next to my bed I have a 30A charger, that charges correctly. I have been inside it and made some "adjustments"... Via anderson connector. Because the XLR charge conectors are crap, limited to 12A max.

Next to my PC I have a couple of 1200 watt 0 - 30V, 0 - 40A bench power supplies. Here I set and charge at 40A and at 28.2V for an hour as I check email etc befor going to the pub. Why? Because anything you do to lower the average depth of discharge also increases battery service life (enormously) too! This puts the bulk of the charge back in an hour. Even 15 mins helps loads!

I also charge using the ultra programmable 40A capable PL8 charger. I do this with lithium, lead etc. And it allows me to graph and control the charge as I do so on my PC. And it measures Ah out or in too. So I can measure the state of the battery every few months too. Overkill for lead batteries but super controlled and accurate. 40A via Anderson connection. 12A via XLR.

I also charge with a ZXD 3000 watt power supply. This can also be configured as a 3 stage charger too. I charge at 50A and at 28.2V again via anderson. OR at 12A via a XLR connector.

I also charge via a split charging system direct from my vans alternator as I drive at up to 100A on the way home whan I have been out. Again this doesent fully charge, but it puts the bulk back in an hour. So again loweres average depth of discharge and makes the batts last many years.

All my wheelchair chargers are on a shelf in the garage unused...
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Re: New Mk batteries for my C300 question

Postby DirtinLa » 12 May 2021, 23:00

Thanx everyone

I am more than capable and have the tools to check my current charger

I may invest in a PL8

I presume its a powerlab 8a v2?
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Re: New Mk batteries for my C300 question

Postby Rollin Positive » 13 May 2021, 00:01

So when you say extend a life cycle make it measurable...using a charger that came with the chair or a newer one will cut the use of the batteries down by months?

For gel batteries how long do you think they should work and be dependable?
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Re: New Mk batteries for my C300 question

Postby Rollin Positive » 13 May 2021, 00:04

Just curious why not upgrade to a new model FW for a smoother ride and better options like seat elevation, lighting, GPS, Permobils newer batteries which support 34s and larger 24s and there new 10 amp charger...
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Re: New Mk batteries for my C300 question

Postby Burgerman » 13 May 2021, 00:40

So when you say extend a life cycle make it measurable...using a charger that came with the chair or a newer one will cut the use of the batteries down by months?


Its impossible to measure it, too many variables.
But ignore other variables, and MK tell you this: download/file.php?id=15645&mode=view

If you do 1 simple thing, such as quick boost charge at 40A for half an hour in the middle of the day, as I do. You will potentially increase service like four or five times. So 5 years instead of one. Or 4 years instead of nine months in my case. Why? Because with any deep cycle lead battery they are destroyed much much faster when they are cycled DEEPER.
You might get 2500 cycles at 50% discharge. But you will get less, much much less at 100% discharge. Maybe 50 to 200 depending on other factors like charging and battery quality. So doing ONE thing, such as a fast charge for half hour in the middle of your day will mean battery life is increased out of all proportion.

If you ignore these things, how much better a PROPER charger, set correctly in months of use depends entirely on how bad your mobility charger is.
Most over VOLT the battery by maybe half a volt. That reduces battery life by HALF. And most undercharge in time, so battery sulfates. So maybe removes another 3 to 4 months or so. So you must MEASURE it.

For gel batteries how long do you think they should work and be dependable?

VERY approx guide
Heavy use? 6 months especially if batts are too small and faster motors.
9 months to 14 months if used hard, grp24 and 6mph average user.
7 years plus is easy if used by an old lady or severely disabled that barely ever leaves the TV or her house. Depends on: Your usage patterns. The size of the battery compared to the chairs speed and user weight. Hills... average distance covered daily. Your charger. And a bunch of other things. And the differences are absolutely huge.

Again when I notice that my range has decreased, or that theres no decent "sharp" control response I replace them because they no longer work for ME. Thats 9 to 12 months in MY case with lead. Going back many years... But if I give that 1 year old discarded battery to a little old lady (as I have in the past), she would think they are just fine, and use them for another 5 years. Why? She doesent go far enough to find out. And they dont deteriorate much as they are not discharged deeply. So who is correct? How do you determine end of life? Batts dont fail. They just get worse. Day after day from month 1 onwards until YOU notice. So the time to replace is when they impact your daily routine.

Or you can use a PL8 charger to MEASURE actual Ah capacity and compare that to new. But again, at what point do you decide they are no longer any use? Officially its whan they lose 20% of original capacity. But I can tell when they lose 5%. Old lady can't tell when they have lost 50%, and 7 years later.
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Re: New Mk batteries for my C300 question

Postby Rollin Positive » 13 May 2021, 16:44

My point being I dont use as much miles per charge as I use to as I get older but still consider myself an active user.

So if I am replacing my batteries (MK 24's $88 a set of 2 under Medicare) each year its a mood point...

If I am up by 7a and out and about with work, meetings, shopping or traveling and out till 10 or 11p that only gives me 8 hours charge so we may short charge one day and top off during the day or long charge the next

With the new Permobil batteries (fast charge and new 10amp charger getting 17+ miles per charge which is more then what I need
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Re: New Mk batteries for my C300 question

Postby Burgerman » 13 May 2021, 17:07

Permobil dont make batteries or chargers. The battery isnt fast charge. No lead based battery can charge faster FULLY in under 16 to 20 hours. Theres no such thing as a fast charge lead battery. You have fallen for the marketing bull. They are using a very slightly more powerful charger. And a slightly lower impedance battery. Net result is that the BULK of the charge can happen slightly faster. But not by much. Total charge time is unchanged. But the CHARGER might well give you a green sooner, to make it all look fast. But its lying to you. Its not yet 100%.

The CLOSEST you can get to that is the (somewhat expensive) Odyssey batteries. Those paired with a big 100A charger can put back 90% charge in 1 hour. But then it still needs a further 8 to 10 hours at CV voltage for a complete charge. So only the first part is faster to 90%. And the only reason that is possible is the low impedance. No other battery has such a low internal resistance.

Their new 10A charger is just 2A bigger than the old one. Sunrise in europe have had a 10A charger on the order forms for many years. I have one here and its junk. A 10A will add the INITIAL bulk stage (the CC stage) 20% faster. Regardless of lead battery brand. But a complete CV stage where current starts to fall to almost zero is still needed for a complete charge. That means at least 8 further hours at CV (Absorption) stage before its fully charged. If you dont do this complete charge frequently (24 to 48 hours on float after charge ends) the battery will soon die from sulfation. So fast charge and lead battery dont go together. Its marketing bull.


You may be fine and batteries last 9 months, up to 7 or 8 years depending on your usage and charge patterns and terrain. Remember that you are light. And your chair has never been programmed so that you can use it agressively. So you will get more miles to a charge by maybe 60% to 80% more, than I would just to begin with.

If someone replaces them for free and you dont care about having decent range at month 12, then you dont need to care. Many do!
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Re: New Mk batteries for my C300 question

Postby Burgerman » 13 May 2021, 17:33

If you were to fit the 200Ah lithium packs as many are now using on here. And a PL8 charger. You can go 5 times as far. Get at least a 10 year battery life. And when charging it can be FULLY CHARGED with 5x as much electricity from fully discharged state after 70 miles use in just 5 hours.

A 200Ah lithium pack has the equivelent usable power/energy/range as FIVE SETS of 74Ah MK Gel batteries... Think about that. And its lighter. And it charges way, way faster! And it lasts at least a decade.

Yes you dont need that much range. Neither do I. That is not the point! You might need it the odd day - say a day out in the mountains, or breakdown miles from any town. What it really does though is stop all of the range anxiety.
You dont need to keep watching the battery gauge. After a few months you just stop looking. You unlearn that fear of "will I get back". You are set free to go about your day, no matter how far, how late all night, as long as you wish to wherever you want. You can go into town for a meal or drinks even after a hard day at an airshow after a day out or something. And you can do it again tomorrow without charging. Thats the real gain.

Over time you just forget about "range" and just go! Get your freedom back. Once you try this you cannot go back. You may not realise this but you limit yourself and what you choose to do based on learned battery limitations. You do it subconciously.

Its exactly the same with the programming. Once you try a properly programmed chair, you cannot go back to what you have now. Even though you think it is fine today! You just cant! Its horrible. Both these things are liberating.

Charging. It can have the equivelent of a full set of grp24 MK batteries "range", added, in just 1 hour. Or 2 sets of MKs in 2 hours. It can be charged weekly. It can be charged in your car. And it is lighter. If you forget to charge, forget it. Do it next week...
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