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Where to source connectors and parts

2Big2B

Free Wheeler
Joined
May 7, 2021
Messages
73
Location
Chesapeake, Virginia
I am building a 8S 12v/100AH pack for a power wheelchair. I will use a DALY LiFePo4 8S 24V 100A BMS (common port - whatever that means) with it, connected with some kind of fuse protection, preferably a breaker switch. I have been following "DIY Solar Power with Will Prowse" YouTube videos. Fascinating.

I am wondering about some of the builds that Will has done that look modular. One video was with Fortune cells, but I think he used the same thing on other brands/types. They look like the each cells fit into independent molded blue plastic base, top and covers - fitting together like Legos. Very elegant. Is that something that is consumer available or is that something custom 3D printed? They would be a neat accessory for someone to sell on ebay.

Below are the type of cells I am using (I don't know what these type are called). Being for a mobility application I wanted 100ah in as light and small a package as possible. I am aware that they have those unfortunate skinny narrow posts and are easily stripped out. I think it has been suggested to use Red Loctite after final assembly to avoid ever needing to mess with them again. I am wondering if I need
specific busbars between these cells? If so, I need to know what to get and where to get them. I also note that most busbars available on ebay are made of various alloys. Copper busbars are much more expensive. Is that an important consideration for what I am building? shall I just find some copper plumbing pipe, and get out my drill gun and a saw? (I am sort of too lazy for that though!)

Also, do I need a fuse and/or an appropriate DC breaker switch between the pack and the BMS. In one of his videos Will suggested a 300amp fuse in one setup that was attached to pigtail cable connector. Overkill? Was that custom made, or can I buy one like that? Would a circuit breaker be better? What specification would that need to be and where should I get that? I have one in mind, picture attached.

I will also need an appropriate battery charger. I am finding very few candidates so far. I am still researching what amperage to get, what exactly to get and where to get one. I can either go up to 10AH to plug in through the chairs wiring, or a lot more with some sort of direct connect to the battery pack.

Any advice?Battey pack busbar.jpg
 

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The Fortune cells come with that casing that allows them to be assembled so nicely.

The fuse goes on the positive side. A Class T fuse is recommended. The BMS goes on the negative side.
 
Thank you!

If I weren't trying to minimize size and weight because of my mobility application I would have gone for the Fortune cells. Their terminal connections are more substantial too.

What size fuse and circuit breaker should I use for this 100AH setup? I was thinking 120amps.
Too much? Too little?

BTW, I found the busbars and charger I need from Aliexpress. It's my first time dealing with them. I am guessing they are a Chinese flavor of ebay. The total price of the charger was $51.41 delivered, after taxes.

Naturally they double billed me! I had an issue trying to process the payment screen. It kept failing. Thinking maybe it was a PayPal credit rejection thing I tried again using my debit card. They billed me $51.41 on both attempts but invoiced me for just one. Dispute via PayPal is in progress.
 
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Fuses and circuit breakers depend on the number of amps you're going to draw. I don't see any information about your loads.

I would be reluctant to use red loctite. While my cells are not in a mobility situation, they do ride in my RV trailer that sees plenty of rough dirt roads. I have no issues so far with the fasteners loosening.
 
Fuses and circuit breakers depend on the number of amps you're going to draw. I don't see any information about your loads.

I would be reluctant to use red loctite. While my cells are not in a mobility situation, they do ride in my RV trailer that sees plenty of rough dirt roads. I have no issues so far with the fasteners loosening.
Thank you for that.

My only concern about fastening and tightening down the terminal connections is that I don't own a torque wrench, nor am I sure what that tool would look like. Hence I would be depending in instinct as far as how tight to try to make them without stripping or breaking a posts. That is where Loctite might come in. So that seems like something I should figure out what to get for torque. Maybe I just put a socket on my 9.6V Dewalt screwdriver that has torque positions on the keyless chuck - which is a bit funky. I am not sure I would want to try that.

I have not indicated power draw because I don't know. That is a mystery until I can field test it, and find the spec on those two massive drive motors - and even that is not perfectly predictably taking account for total weight and terrain. The load on the motors is a function of the weight being transported which of course governs the current draw.

My best guess is to take into account that this battery pack should max out at out @ < 100AH and that's what my following logic is dependent on. Or is there something I don't know about some variance in maximum current output of LiFeP04? I believe LiFeP04 can only operate within a tight voltage range which is why you use a BMS to manage and protect the cells from overcharge and undercharge. I don't see how the battery pack could provide more power that 100A - or is there is something I don't know (which is why I am here.)

Other than that, the rest of my logic seems bullet proof.

Anything beyond 100A that in this context by definition is a dead short. Hence I am betting that a 120 amp fuse is a good choice, just to be on the safe side. The higher the fuse value, the slower it burns. And if I put a weaker circuit breaker in front of it , it should trip first.

Or is there something I am missing about LiFeP04? As I understand it, the nature of those batteries operations is based upon a narrow voltage range with specific endpoints of capacity. I think. As for the fuse, it's function is protection against a catastrophic event like, say running the chair into a lake. Otherwise the Circuit breaker downstream handles operational protection. It should be of a lesser trip value - and that I guess exposes the question of what value circuit breaker to use. The answer to that depend upon correctly anticipating maximum load. Hence I am thinking that setting the breaker to say, 80% of maximum current ever available: 100A. An 80A circuit breaker should suffice. If it trips it will probably be telling me to slow down on wherever I am going. And that is a good thing.

My hunch is that in reality the power draw will be between 40 and 60 amps while running full power continuously on flat terrain. Less for just socializing, going a mile to the grocery store and generally cruising around town. So an 80 amp circuit breaker is probably about right. Worst case, I make a wrong estimate and have to replace a circuit breaker or fuse. They are not that expensive.

There's my logic anyway.

Hence an 80 amp circuit breaker and a 120 amp fuse.

What do you think?

(callsign: N2MZN)
 
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I'm not going to give you an up or down vote until you know the rated amp draw. Guessing is not a good way to arrive at what current protection to use.

Somewhere on the Internet, I bet the manufacturer has published the specs.
 
Well actually it isn't anywhere on the internet. But I was able to get the manufacturer to send me pdf files of the manuals that go with this. There is enough there to make an encyclopedia - so the amperage of the electric motors and brakes will be buried in the Service manual somewhere. I will attend that presently. I am guessing they are rated at 30A each. I expect the brakes are run off of a momentary solenoid that lives off the back of each motor.

SOLVED!

Extracted from the User's Manual, the original configuration called for a "Dual Mode 24V/8A Gel battery charger, and that it uses a 70A circuit breaker.

(Digging deeper), Extracted from the Control Panel Programming Manual I found a wiring diagram of the battery power system. It was buried pretty deep in that manual, and the volume of information between the Safety Guide, Owner's Manual and the "UE1B UEID UEIE Universal wheelchair Electronics Owner's Manual' (-even the title is exhausting), I discovered a diagram that shows the original configuration with two 12v 105A SLA batteries in series. It lays out the details. Apparently there should be a 70A circuit breaker attached to the harness. It sounds like I can use the existing circuit breaker if it is still there! They say it is to protect against any catastrophic operational event.

Circuit breaker diagram closeup.png
I am still inclined to insert a 100A fuse downstream to the BMS that I am installing for this conversion.

And that takes care of that!
(actual mileage may vary)


Now that I have done the groundwork, this thread probably needs to be moved into its own new forum that is likely to become an upcoming new niche application - POWER WHEELCHAIRS.

- STAY TUNED -
 
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I have an older Quickie P100 power chair. It has a 24V system. The AGM sealed lead acid batteries that came with the chair are 12V Deka 8AU1 32 amp hour. They recently stopped taking a charge and I happened to have two 12V Ironworks LiFePO4 44.7 amp hour batteries. The battery boxes have a tray for different sized batteries and a 30 amp fuse. The Ironworks were a perfect fit.

Each battery box has an Anderson type SB175 connector that plugs into the 24V power controller. There are circuit breakers on the power controller, but I can't remember the rating. There is a proprietary plug from the power controller to the joystick/speed controller.

The 24V charger plugs into an SLR jack on the joystick/speed controller. The charger states "Lead Acid Batteries" so I picked up a LiFePO4 charger just to be on the safe side.

Another forum member posted a link to a power wheelchair group. Their members advocate LiFePO4 batteries WITHOUT a BMS. It seems the BMS may cause performance issues with a power wheelchair. The Ironworks battery has a BMS but I don't run my chair that hard and I haven't had the issues the power wheelchair users address.

http://www.wheelchairdriver.com/
 
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Thank you for your comments.

I just received my NOS Bounder power chair that I bought on ebay. It came without batteries but was designed for a pair of 12V Group27 105Ah gel batteries. For a test drive I used some nearly dead 12v 55Ah AGM batteries and took it for a spin. I got a couple of miles out of it before it started to wind down. Later I will swap in the fresher 12v 55Ah Gel batteries from from my Golden Compass chair. That will have to suffice until I get my 100Ah 24v pack built. I will swap the old AGM cells back into the Golden Compass which doesn't need any range, being my house chair.

I am inclined to use an Overkill 8S 24v 100A BMS with the 8 Liitko 3.2v 100Ah LiFepo4 cells on order. That should work fine. And yes, you do need to use a proper charger for LiFepo4 cells. Unless you are very careful and maintain extreme vigilance in checking the balances I think it would be a mistake not to use a BMS.

I speculate that later I might try to buy another set of those cells and double up the capacity when prices drop.
 
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