Modifying the Eagle HD - Electra7 for standard batteries

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Modifying the Eagle HD - Electra7 for standard batteries

Postby Gnarlodious » 13 Jan 2022, 18:42

Hey people, first post! I picked up a broken Eagle HD power wheelchair for a mere $120. It was missing the batteries and had a smashed motor, but that repair is for another post. It seemed like a strong, well designed and high quality machine suitable for rough terrain, so I was willing to spend on repairs. This post shows how I bypassed the unreasonably expensive custom batteries and modified it for standard batteries, after a few false starts. As it was made it was a nice system but the batteries were completely specific to this wheelchair (and the Electra 7):
front.jpg
The original batteries slid inside the gaping holes down into the square frames, it was two of the 24 volt batteries wired in parallel.
I made a battery holder from hardware store aluminum bars hung from below the seat, this allows the wheelchair to be folded up as designed:
bottom.jpg
I used shrink-tube with internal hot-melt glue for a resilient and grippy wrapper over the smooth aluminum. In this setup I use two of the 12 volt batteries wired in series. NOTE: Not an ideal arrangement unless you have some understanding of lithium batteries. The use of 2 12v batteries gave me more options for use of available space, since the wheelchair needs to fold up, and available 24 volt batteries are larger in every dimension. 12v also allows me to charge them directly from my van's auxiliary 12v system, and also to use the wheelchair batteries for van power in a pinch. I would simply need to change the plug-in wiring adapter shown in the next picture.
Here is how I wired 2 12v batteries in series for 24v using the Anderson Powerpole connectors:
powerpoles.jpg
The red 180º bent wire runs diagonally across the four-ganged connector for the series wiring, and likewise the black negative wires goes diagonal. Strangely enough, I found no instructions anywhere on the internet explaining how to do this. The downside is that running this way for several charge/discharge cycles, while charging with a 24v charger, will result in a charge state imbalance. However charging the batteries in parallel at 12v keeps them equalized. A slight inconvenience I am willing to tolerate for the advantage of versatile 12v batteries.
The batteries are two of the 12v Bioenno LiFePO4 battery BLF-1212A size 8.5x2.2x3.1", laid down on the short side. I bought them and the wiring supplies from Powerwerx.com.

I searched the internet but found no information on how to do this mod. I hope this instructional helps someone as these wheelchairs get older and the original batteries get hard to find.
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Re: Modifying the Eagle HD - Electra7 for standard batteries

Postby Burgerman » 13 Jan 2022, 20:28

You could re-cell the lithium ion 7S that they come with if you had the dead ones. Those end up lighter for the same capacity which is why they use them. But are a potential fire hazard and are short lived just like your laptop battery.

The problem with lithium ion is that if you use most of the capacity they have the same cycle life as lead. So lifepo4 is a better and safer solution. But they really dont like BMS for charging as they are very particular how they are balanced and charged. So you wont get anywhere near the decade of use and 2k cycles that they are actually capable of. Some of my larger packs are as good as new and nearly a decade old. But with small packs like those it doesent much matter as they are relatively cheap.
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Re: Modifying the Eagle HD - Electra7 for standard batteries

Postby Gnarlodious » 14 Jan 2022, 00:32

I didn't get the battery packs so it doesn't matter, I figured someone scavenged them for the cells inside. The wheelchair also came with no cushion, a shattered fender and that side's motor had its wires ripped out and the manual lock sensor was smashed, as well as other missing parts. I might have repaired the motor but I don't have the capability since I live in my van. I think (hope) the charge indicator lights will work the same on polymer batteries as the ion batteries? If not I can put a pesky voltmeter on it to monitor performance. I don't expect to run the batteries much below 20% charge just because I am afraid of getting stranded.

In general this wheelchair is sort of jerky and primitively controlled. I suspect the newer ones are smoother in the controls Thanks for your comments. There seems to be a dearth of information on this wheelchair, its parts and repairs.
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Re: Modifying the Eagle HD - Electra7 for standard batteries

Postby Burgerman » 14 Jan 2022, 00:51

The reason its hard to control is that it needs programming properly. But depending what controller it uses that may not be possible. It may be all chinesium parts that nobody undestands here...

The voltage limits definitely are very different. It used to have a 7S lithium ion. Which is fully charged at 29.4V and as it discharges it remains high, and the discharge curve is basically very uniform. And so both a BMS and a battery guage can give sensible results. I.e lower votage = lower state of charge in a linear fashion. You SHOULD charge lifepo4 8S at 28.8V maximum. But in a vain hope that they will sort of self balance, with the typical hopeless BMS then the manufacturer specifies 3.65V per cell. So its charged TO and AT 29.2V. Which shortens service life. But ignoring that, as soon as you end the charge the voltage begins to drop. Even sat there. So that by morning the voltage will be 3.5V or less anyway. And yes its still fully charged. Then as you drive it it will drop fast to around 3.3x volts and stay there or even rise slightly depending on load (cell temperature). And so as you drive along using your battery its charge level will maybe stay the same for haf the charge. Or it may increase a little depending on how much you load the battery. So your meter will make little sense. It will seem as if the battery will last forever. Right until it doesent...

Also the battery will chop off power when it sees too much load and it can only do 20A... And it may stop at 24.5V on monday. But at 25.5V n tueseday. Because that depends on proper balance. As it will stop the chair when it sees the first cell reach its programmed lower limit. Which will be at a cell damaging 2.5V.

You live in a van?
I might worry about those nuts breaking through the blue plastic. Every cell is connected in series. And the CASE of the cells are connected to the negative. Meaning that if two cells metal casing touch, or are connected by those nuts, you will have sparks, smoke and damage.
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Re: Modifying the Eagle HD - Electra7 for standard batteries

Postby Gnarlodious » 14 Jan 2022, 16:15

This is my first experience with LiPo batteries and since it is a mission critical application I want to be careful to monitor their charge. I have read that emergency responders have a high rate of calls from people stranded in electric wheelchairs whose batteries are dead. As it turns out, the batteries are usually not dead but rather the BMS shuts it down for reasons I don't completely understand. Especially applies to me since I am running two 12v batteries.

And yes, I will put some clear vinyl tube over those exposed nuts. I do live in my van, so these wheelchair batteries may be used as auxiliary batteries during off-grid sessions. I just need to be careful to not charge them while it is below freezing weather.
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Re: Modifying the Eagle HD - Electra7 for standard batteries

Postby Burgerman » 14 Jan 2022, 17:43

The BMS is the single most problematic thing with lifepo4 type cells in both is "protection" job which leaves you stranded for a bunch or reasons, and in the way they charge/balance. If the battery is large enough for the job, then it willl not keep cutting out at all which is great and then its not required... Except for charging.

And they are spectacularly bad for this remaining purpose too. So its much better to have a huge reserve of capacity, an so range is much higher, and this loads up and works the cells much less too. And means no BMS is required to protect the cells from too high current and the voltage drop from overloading also does not happen and so the cells live longer too.

What LiFePO4 HATES:
Heavy currents.
Being full.
Being empty.
Being USED or CHARGED cold.
Being stored at high charge. Best to store at 70% or lower.


So charging to an exact 3.550 per cell, and never discharging below say 80% will mean a very long service life. And never pulling high currents from the calls (high C rate). That rules out relying on a BMS and dumb charger. It also means using a high capacity pack as possible. And charging with a good cell balancing charger. Like the hobby style ones.

With the chairs we are mostly using on here, we remove the lead 75Ah batteries and replace with 200 to 230Ah LiFePO4. Because the capacity is possible in the exact same battery area/volume with careful monitoring. This results in a very low draw in amps from a pack compared to its capacity. And a range increase from a claimed 25 miles. to five times this. In reality the real world range on lead is 15 miles. So you get around 75 mile on lithiums. But because thats more than you can realistically use/do in a day, then running too low simply doesent happen. This results in "endless" range, low loading on the pack, low average depth of discharge, and charging every 3 or 4 days or so in winter. So the pack lasts a decade plus. Instead of a year... And no BMS needed or wanted. And proper charging and balancing. You get around 50% extra range per Ah with lithim compared to lead. So 3x the capacity = 5 times the range. And a vastly improved calender and cycle life to boot.

I have read that emergency responders have a high rate of calls from people stranded in electric wheelchairs whose batteries are dead. As it turns out, the batteries are usually not dead but rather the BMS shuts it down for reasons I don't completely understand.


People break down because thy fit a BMS equipped lead brick replacement of the same capacity which is not adequate for the job. So the BMS stops the chair.
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