Can you help me figure this one out…bms free

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Can you help me figure this one out…bms free

Postby Kssisk » 04 Aug 2021, 15:25

I am in a bit of a pickle. I am trying to build a 24v emergency solar generator. Due to them shutting the bridges down and getting stranded with no gas or power for a week or more. I have some medical stuff, a modem and router, and charger for my power wheelchair that I need to use.
I have 2 of these battery banks with no bms from batteryhookup.com. 25.9v 32ah 828.8wh SPIM08HP 24v POWER Module 7s 4p https://cdn.shopify.com/s/files/1/2398/ ... 1625886189 I want Inverter 2000 or 3000w pure sine. Charge controller maybe a 40-60a mppt? Panels thinking (2) 24v bifactual 450w.
I can read sematics but can not figure out how to make the something work to protect the batteries (assuming I need one)
had a lightbulb moment- could I Perhaps use a active cell balancer instead. Putting a fuse or small miniature circuit breaker after the batteries but before the inverter (200a ?).
I am just worried about discharging the batteries to far. I would like the idea of a low voltage cut off.
All solar places say use a bms
I know that the batteries are small but I need it portable and light
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Re: Can you help me figure this one out…bms free

Postby Burgerman » 04 Aug 2021, 21:18

I am in a bit of a pickle. I am trying to build a 24v emergency solar generator. Due to them shutting the bridges down and getting stranded with no gas or power for a week or more. I have some medical stuff, a modem and router, and charger for my power wheelchair that I need to use.

You wheelchair presumably has 70Ah ish batteries? And you may need to charge them maybe 40Ah? IN?

I have 2 of these battery banks with no bms from batteryhookup.com. 25.9v 32ah 828.8wh SPIM08HP 24v POWER Module 7s 4p https://cdn.shopify.com/s/files/1/2398/ ... 1625886189


You need to use either a solar charge controller that can balance batteries, or a solar charger that can do 29.4V or a fraction less, with a BMS. I hate BMS normally but thats because we are all charging LiFePO4 and your cells are 7S Lithium ion. A lithium ion pack can be charged and discharged with a BMS fine as they dont have the same super flat voltage discharge curve that LiFePO4 cells do.
I want Inverter 2000 or 3000w pure sine. Charge controller maybe a 40-60a mppt? Panels thinking (2) 24v bifactual 450w.

Yep.

I can read sematics but can not figure out how to make the something work to protect the batteries (assuming I need one)
had a lightbulb moment- could I Perhaps use a active cell balancer instead. Putting a fuse or small miniature circuit breaker after the batteries but before the inverter (200a ?).
I am just worried about discharging the batteries to far. I would like the idea of a low voltage cut off.
All solar places say use a bms
I know that the batteries are small but I need it portable and light


For something charged intermittently by the sun you are going to need some kind of BMS. Theres many... But theres no alternative.
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Re: Can you help me figure this one out…bms free

Postby Burgerman » 04 Aug 2021, 21:29

Be aware when looking for a solar charger, and a BMS that unless you want a very short lifespan on those lithium ion cells then you should not charge them above around 85% or below around 15% in discharge.

If charged to the full 4.20V per cell, then they will last 1 year to 18 months stored. Aim for 4.1V pwr cell as they will last 3 or 4x longer. 2K cycles instead of 500. But you will be sacrificing around 30% of overall capacity.
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Re: Can you help me figure this one out…bms free

Postby Kssisk » 04 Aug 2021, 21:48

Thank you for the awesome response
I learned a lot [*]t
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Re: Can you help me figure this one out…bms free

Postby Kssisk » 05 Aug 2021, 00:03

I do not know where the [*]t came from
My phone is doing weird things
I apologize to all
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Re: Can you help me figure this one out…bms free

Postby swalker » 05 Aug 2021, 01:02

I will start by saying I am a proponent of solar power and have used it before.

I will also say that I am in a similar situation to you. I live in the mountains of Colorado where we can and have had situations where power and supplies are not available. So, I needed to have a backup solution for power.

The only way solar would work for my needs would be if I had a large enough battery bank to store sufficient energy to last me through any anticipated outage. I could not rely on the sun to be shining sufficiently during an outage for me to collect sufficient power for my ongoing needs with any practical size solar array. Thus, I would have to collect the energy before an outage and store it in a battery bank (or other energy storage device).

In your situation, you want to have enough energy to last for a week. Your storage bank will be 64 Ah at 24 volts (about 1650 Wh). I can't see how this would support the needs for a typical household for a week. I especially do not think it would support the needs for keeping your medical equipment going and charging your wheelchair. It certainly would not satisfy my needs. As burgerman said earlier, a pair of group 24 batteries in a wheelchair are rated at 74 ah at 24 nominal volts. While you would never put this into the wheelchair at one go, it would be easy to need 35 to 40 Ah at 24 volts to recharge the wheelchair each day. So, unless you live in a place where you can reliably get enough sun to recharge your batteries daily during any potential outage, I don't think solar will meet your needs.

It was pretty easy for me to conclude that solar was not the right solution for us. Instead, we have a pair of Yamaha gas generators. One of those is sufficient to provide the power that is essential for us. We keep enough gas on hand to power the generators to get us through any anticipated outage. That is a simple, reliable, and cost-effective solution for our backup needs.

After looking carefully at your energy needs and comparing it to your ability to collect and store energy from a solar array, I think you will find that your currently-contemplated system is simply insufficient.

Steve
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Re: Can you help me figure this one out…bms free

Postby Kssisk » 05 Aug 2021, 01:05

So if I set my charge voltage to cut off at 28.7v (4.1v per cell)
And the low of 20.2v (2.9 per cell) I should be ok
Bad thing is I loose about 30% of my 64ah rating? Effectively a 45ah battery (1.1 kw battery)
But gain in cycle life (about 2000)
Trying to find a SCC with cell balancer
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Re: Can you help me figure this one out…bms free

Postby Kssisk » 05 Aug 2021, 01:36

Basically the chair would not be charged every day with a outage because I would not be going anywhere ( on a coastal NC island) the bridges would be shut down. Realistically I can get 8 hours of full sun. I based my chair usage on being home bound like I was after my surgery and I charged it every week and half.
I have 2 grills for cooking (lp and charcoal)
Propane heaters
No appliances needed

Needed are
CPAP
Router and modem

Would like
Are TV (one)
Fire Cube

All are not on at once
I figured I could charge the battery during the day and use it during the night for the CPAP
Typically
Modem is 7w
Router 7
TV 150w
CPAP about 5W with it running 8 hours or less

I just need something portable and my wife can set up
We do not have the ability to store gas so it’s between a rock and hard place
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Re: Can you help me figure this one out…bms free

Postby swalker » 05 Aug 2021, 02:29

I understand that we sometimes need to make compromises based on where we live. In my case, I love living where I do and have to make quite a few compromises to keep living here!

You said you are planning to use an inverter. It is likely you have already considered this, but you should avoiding the conversion to AC and then back to DC for devices that can run off of DC power, such as a CPAP.

I use a non invasive ventilator (like a CPAP, but a bit more sophisticated). I have a 12 volt DC adapter for it so I can connect it to a DC outlet that is directly connected to a 12 volt lead acid battery. That is one of the backup solutions I have in place for it (just in case both of the generators somehow fail).

If the gas storage is the only roadblock to using a generator, then you could consider a propane fuel generator (though, you likely would not have a place to store propane either).

Steve
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Re: Can you help me figure this one out…bms free

Postby Kssisk » 05 Aug 2021, 03:27

Thank you for the information on the CPAP I will look into it I have a resmed air10. Did not know they might be able to run off dc. I agree with you on the living situation, I feel the same way.
I have no place for a propane tank originally we were looking at gas or propane route
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Re: Can you help me figure this one out…bms free

Postby Burgerman » 05 Aug 2021, 09:43

Its the same when it comes to charging your chair. A PL8 like we use here for lithium conversions - a cell balancing charger that can charge all chemistries, inc lead will run from 10V up to 30V and charge at up to 40A - you decide. No need to waste 15% going up to AC and then down again losing another 15% with your chairs AC charger. I might add you should charge lead daily. Not weekly no matter how little its used.


I might also add that you will likely never see that 450W x 2 from your solar panels. In winter you will get 10% of that. In summer at times like 12 noon, after a shower to cool them you might see 85% of that for a few mins. The rest of the time they will, if aimed directly at the sun doe 50 to 65% of the max rated, for 4 or 5 hours a day.

So you probably want to be looking at a lot more solar. Esp in winter or dull days.
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Re: Can you help me figure this one out…bms free

Postby Kssisk » 05 Aug 2021, 13:25

Thank you so very much for the info
:thumbup:
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Re: Can you help me figure this one out…bms free

Postby swalker » 05 Aug 2021, 20:42

You said you live on a "coastal NC island". If by NC you mean North Carolina, you will get more solar in the winter than Burgerman gets because you are quite a bit closer to the equator. Still, he is right that you will never see close to the rated output from the solar panels.

You can't control when the sun shines, how much atmospheric degradation there is, and, to some degree, how many shadows fall on your panels. Note that even a thin strip of a shadow (such as from a naked tree branch) can tremendously affect the energy you can collect. The type of solar panel and type of controller can make a big difference when the panel is going to be partly in shade.

You can control how clean the panels are and to some degree what direction they are pointed.

Be sure to factor all this in when sizing your solar panel array.

Steve
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Re: Can you help me figure this one out…bms free

Postby Kssisk » 06 Aug 2021, 02:41

Correct on the North Carolina
No trees or shade where I would like to set up
I agree with everything that has been said
I understand that I should be topping off the lead bricks every day
Can I ask why?
Also does not percot apply to lithium ion? Or just lifepo4?
I have a progressive neuropathy that has me now relied upon the chair so I am late to the game
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Re: Can you help me figure this one out…bms free

Postby Burgerman » 06 Aug 2021, 13:12

I understand that I should be topping off the lead bricks every day
Can I ask why?
Also does not percot apply to lithium ion? Or just lifepo4?


Lead...
Takes 16 to 20 hours to FULLY charge in spite of what your mobility charger tells you. When you get the green ready light, its STILL CHARGING but at a lower voltage known as a float voltage. Why is this important?

If you drive a fully charged chair 10 feet you took a little of its charge. If you just turn it off, the chair still removes some charge very slowly. If you dont move it or use it charge every 7 to 10 days ideally. If you move it AT ALL charge overnight at least.

Why does it matter? As you discharge a battery the lead plates are coated in lead sulfate (and lead dioxide) as the acid in the electrolyte is used up. This is in the form of a super fine conductive layer. So as you FULLY charge which takes around 12 to 16 hours regardless of discharge amount, this layer gets returned back to the electrolyte/acid. If you dont complete this, then it turns into a layer of larger xstals that do not conduct. At this point some of the battery capacity has been lost forever. It does this faster the more discharged it is. And the warmer it is. And the longer its left before topping up. Once its bad enough it goes in the rubbish pile. And is not reversible no matter what the snake oil saleseman tells you.
Also the deeper you discharge a lead battery the shorter its life. Quite drastically.Because as well as causing sulfation, it uses up the active plate materials faster. So charging weekly when used regularly is very harmful for these two reasons.

Lithium HATES to be empty. And HATES to be full. It lives longest by far if kept between 20% and 80% charged. Should never be stored fully charged! If storing more than a day or so then disharge away from the full point. For long term storage 65% full is perfect.
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Re: Can you help me figure this one out…bms free

Postby Kssisk » 22 Aug 2021, 05:23

Would this include sla gel batteries?
Do gels have a advantage with usable capacity over a sla or AGM? Would the range be the same in a 100ah gel vs a 100ah AGM
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Re: Can you help me figure this one out…bms free

Postby Burgerman » 22 Aug 2021, 09:13

If all were 100Ah then the battery with the lowest impedance (which is generally the most expensive) would give the greatest control and torque and range.

Its all a balance. When making a battery there are 3 things that have to be balanced against each other. If the case size remains constant then you can do any of these things:

- Maximise capacity. Say 100Ah. And either cycle life, or impedance (internal resistance) suffer.

- Maximise impedance (low mOhm internal resistance), and Ah or cycle life suffer.

- Maximise cycle life, and then Ah or internal resistance suffers. And this is usually the case with deep cycle batteries.




GRP24 sized:

So where does this leave us. I recently bought some "cheap" AGM batteries with 80Ah, and 500 cycles. (500@80% DOD). In a group 24 sized case that means that the Ah on these is relaively high, although 100Ah is possible. But cycle life is excellent. But they lack the "power" to climb a curb well, or to "wheelie". Does this matter? Well compared to my usual choice of 68Ah Odyssey batteries they feel as if the "battery is flat" performance wise. And so not great. And range is around the same as the smaller 68Ah. So range depends on internal resistance too.

So if you want a battery to have a little pep. If you want a lot of range then you want a battery with low internal resistance.
If only range matters then a low impedance, high Ah battery matters. Like a 75Ah starter battery! But you will only get a couple of months inn deep cycle service in a chair.

Ah alone is useless. A 100Ah battery with high impedance will not work your chair well and will give less actual range due to voltage drop under the heavy load a chair needs in use.

So what to use. Is it possible to get all 3? Not really. You can get closer to it with a little expence...
-Odyssey AGM is the lowest impedance of all batteries at 2.5mOhm and the highest cost. I use those. 450 cycles, great performance. average range. Best for high currents so chairs programmed to acelerate hard, heavy chairs and users, sport. Charges faster too.

-Cheap AGMs which is most of them. AVERAGE range even with higher Ah. And 300 to 350 cycles. These vary and some have greater cycles/but higher impedance. Of 6 to 10mOhm which is crap!

-GEL batteries like MK offer above average performance, excellent cycle life 550 if charged CORRECTLY, and are adequate and best for the average user. 4 to 4.5mOhm.

Does that help?
Good Ah in this sized battery is 90 to 100Ah.
Good cycle life is 500 to 550 @ 80% DOD and only MK or other gel generally achieve that.
Good impedance is 2.5 max. Thats only achieved with Odyssey. (4 to 4.5 for MK gel, higher for cheap AGMs)

Only Odyssey or MK gel generally achieve enough of all 3 to be good wheelchair batteries. And only MK gel are commonly used. So now you know what to look for. And what the compromises are!
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Re: Can you help me figure this one out…bms free

Postby Burgerman » 22 Aug 2021, 09:35

Why is Impedance (ac measured resistance) all important? Because its also a extremely good predictor of the surface charge effect. A chemical reaction that occurs between th surface of the plates and the electrolyte.

If you pull a lot of amps from a lead battery by climbing a curb, or starting a car, or even by driving full speed for 2 hours (at even 6mph thats 12 miles and your chair stops moving.) It does this at around 45 to 60% of actual discharge level. The voltage falls under load. And takes 24 hours to recover. This is the surface charge effect. (peukert.) The battery runs out of steam in the short term. And you stop. Much like you crank a car till it stop turning. And the next day it can be cranked all over again without recharging (and it may start).

So low impedance means less voltage drop under load. And less peukert too. And for sudden very heavy loads like say a wheelie the low impedance battery can do it. With a set of cheap AGMs in my chair it will NOT wheelie at all. And steer is effects and it feels vague. So both Ah and impedance determine USABLE capacity.

For e.g, an ODYSSEY 68Ah battery will give the same range or better range at high loads, hills, etc. Compared to the 74Ah MK. So Ah isnt everything. The MK wins if discharged over 20 hours. Which we dont do. Remember 2 hours driving at 6mph is all of your chairs range. So the 2 hour rate is what matters unless you just sit drinking tea most of the day.
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Re: Can you help me figure this one out…bms free

Postby Kssisk » 22 Aug 2021, 18:22

Thank you
I am learning a lot
I currently have 2x 60ah Mk sla gel 34m batteries in the chair. Once they get one or two ticks down they deplete rapidly now.
I now understand that because of the make up of these performances wise they are probably better than a lot of 100ah Deep Cycle batteries.
I am assuming that the Deka/Mk 8g34 is the same.
So lower # for resistance are better with a higher discharge rate and possibly a smaller footprint and saving in weight?
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Re: Can you help me figure this one out…bms free

Postby Burgerman » 22 Aug 2021, 18:59

You can only compare batteries of equal case size (or volume).

Thats the limiting factor.

And so a grp34 which is the same footprint as a group 24, only the 24 is a little taller cant be compared directly.

Because the group 34 will have higher impedance, and lower capacity and similar cycle life even if both are the same MK gel.

But its not so simple. Because the GRP34 has less capacity, every trip you make removes a greater amount of charge as a proportion. And the depth of discharge is a HUGE determininf factor in how long they last before they are end of life. And so they die much sooner. Its a death spiral. Because as they deteriorate faster, you discharge whats left deeper as a percentage every day.

You may get 5000 shallow cycles. 1500 60% to 70% discharge cycles, 500 to 80% used, and only a handful of complete discharge cycles. And proportionally you are also discharging the smaller group 34 at a HIGHER RATE and so theres even less USABLE capacity available before you stop too.

So a chair with grp 34 batts will likely eat batteries at twice the rate the same chair will with otherwise identical grp 24 ones.

All provided they are CORRECTLY charged. Heavier batteries almost always = better. Unless you are comparing to lithium.You should always fit the largest batteries possible in your chair. And chairs with only group 34 are at a huge disadvantage. Worse still are those with 22nf sized ones... Only suitable for short trips and sitting at home. And slower motors. The fact is that even the best lead batts are not really up to the job on modern heavy powerchairs at all.
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Re: Can you help me figure this one out…bms free

Postby Kssisk » 22 Aug 2021, 19:58

I also need to get batteries for a home built handicap scooter ( my dog walking and outside scooter) made by a friend for me http://www.leebell.net/pclone2.htm. So I have room. From your recommendation I should go with the largest odyssey battery I can fit. Is there a certain type (red top? Car?) do you have any experience with optima?
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Re: Can you help me figure this one out…bms free

Postby Kssisk » 22 Aug 2021, 20:01

What is a PL8 charger
I can’t find anything on them
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Re: Can you help me figure this one out…bms free

Postby Burgerman » 22 Aug 2021, 20:03

I would. You wont like the price. Or the weight. But personally I would never buy lead today when you will get 5x the range with lithium in the same battery volume at half the weight.

15MPH? Wont work with 24V without murdering the motors and batteries. Tall gearing is not the way to go. You need to use lower gearing and 48V.
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Re: Can you help me figure this one out…bms free

Postby Burgerman » 22 Aug 2021, 20:04

PL8 has just been finished. Company has shut up shop end of the month.
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Re: Can you help me figure this one out…bms free

Postby Kssisk » 26 Aug 2021, 19:23

The Vmax Batteries have a have a internal resistance of 4.3 or lower
Deep cycle, high performance
Just a FYI
I have been asking around, thanks to my new found knowledge from you
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Re: Can you help me figure this one out…bms free

Postby Burgerman » 26 Aug 2021, 19:48

Thats the same as MK gel. But HALF as good as the lighter grp34 68Ah Odyssey. HALF! Those are 2.5mOhms. So when almost flat will still start a truck. So you would need 2 of those Vmax batteries to match its high current capability.
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Re: Can you help me figure this one out…bms free

Postby Kssisk » 26 Aug 2021, 20:09

That is true
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