Lithium battery upgrade for mobility scooter

Diamondback

Diamondback

10 kW
Joined
Dec 15, 2008
Messages
540
Location
Sydney, Australia
Hi all.

It’s been quite some time since I posted anything in the forum. Life kinda got In the way.

My father (79) has a few health issues and few years ago I bought him a scooter. It’s a 3 wheeler. It has 2x12v sla 28ah (supposedly 28ah) batteries in Series for 24v.

The lead is not giving anything like the range it used to. And it’s taking ages to charge. So I’ve ordered a 24v 30ah ping battery and charger combo for it.

That part I’m good with.

I have a quick question about the bms and cooling for it when charging. The pack will be mounted inside a plastic tub under the seat of the scooter without much airflow.

I want to hook up a 24v fan that will automatically turn o. When the charger is plugged in and stop when unplugged.

Does anyone know if I can just tap off the wires going from the charger to the BMS to power the fan ?
Or would this just back feed the fan off the battery when the charger is unplugged?

As this is for an older man, who has health issues, I need it to be fully plug and forget. No switches to remember to turn on or off.

Could I run a diode to stop power back feeding the fan from the battery ?

I’m still waiting for the battery to arrive , after stupid customs sent it back to China. With no reason given.




Jason.
 
Generally yes, the BMS will feed power back through the charging connector, some designs actually have them directly connected together.

Depending on the rate of charge, you might not need to worry about cooling at all, I'd say 5 or 6A would be totally OK.

The simplest solution, that would also cover cooling while discharging, would be a thermostat set to turn the fan on at say 100F. Should be fairly easy to come by in 24V, sounds like the kind of thing that might be found on a commercial truck.
 
A thermo switch hadn’t really occurred to me. , but given where we are, summer often sees days much hotter than 30°c so would have to be careful that a temp switch doesn’t drain a parked up battery either.


The charger we have coming is a 4A unit.
And the scooter is only 400W brushless dc.
So not too high powered.

Jason
 
Given the size of the battery and the very low amount of current you're asking it to handle I don't think you'll have much to worry about even without active cooling.

Another way to tackle it might be using a 4 pin connector set for the charger, with 2 of the pins on the scooter side going to the fan. You'd bridge the 2 sets in the charger side plug, so the fan would be connected only when the plug was inserted.
 
Thanks.

I like the 4 pin idea.

Edit. Thinking about it, I should be able to achieve this using the current 3 pin xlr charge plug it has now.

The negative side of the fan can run to the battery charger directly (scooter side) and the positive line in the charger side plug can be bridged to the 3rd (currently unused) pin.
Then run the fan positive wire to the 3rd pin scooter side.

Thanks heaps for the idea. I know that given the lower power requirements, both charge and discharge, the fan is probably overkill. But I just want to make absolutely certain that I don’t have any heating issues.

Thanks again.

Here’s a pic of the scooter and it’s owner.

6DEB9F0D-0054-4BBB-9DC5-3D24EA09DD5E.jpeg
Jason.
 
You're right, 3 pins is enough, I should really sleep one of these nights.

The logical next step after improving battery cooling is to make it go much faster.
 
Not with the way he drives already. Lol.

I could hide a “turbo” button somewhere though ;)

Jason.
 
G'day boys & girls.
First, here's something you might consider.
One of reasons mobility scooters use lead acid batteries is all that weight down low helps stability.
'nother thing you should know. The XLR charge socket uses the third pin ( green wire ) as an inhibit signal so the scooter can't be driven if the charger is plugged in.
You might want to look into "Fusion" LiFe batteries. They're signed as drop in replacement for SLA, are the same size & shape & the BMS can even use an SLA charger though I'd recommend getting a 8A unit.
Good luck!

AussieRider
 
I didn’t know about the drop in option. I’ve already ordered the ping battery. So have to make that work.

This particular scooter only uses the 2 pins on the xlr plug.
It’s a cheap Chinese import. (Cheap is relative when it comes to mobility scooters)

Good point about the weight. Hadn’t considered that.
Might have to add extra to compensate. Last thing I need is for him to tip it over.

I will post a few pics after the battery is finally installed.


Jason.
 
Hey DB.
Standard mobility chargers have the third pin ( ie, inhibit ) shorted to positive in the plug. If your XLR charge socket has 3 pins, you could do the same thing & power the fan from the middle pin whenever the charger is connected.
I used 4 Fusion batts in my EVT 168 with limited success. Charges ok from the OEM SLA charger & doubled my range but limited acceleration because the BMS only allows 10a continued with 80a burst for 10 seconds. Not enough with a 1400w motor / 120a controller combo. Take it easy & it's ok but punch it & one of the batts shut down for a minute.
 
The battery has been installed and works great.
First full charge got him just over 30km range and the battery took roughly 27ah to recharge.

Plenty of range.
Now all I need is to find a decent SOC meter for it.
Doesn’t need to be a current shiny type. Just based off voltage would do. So he doesn’t go getting stuck somewhere with a flat battery.

I tried a meter off eBay, but it’s wildly inaccurate.
It was still showing 100% (no load) at the bottom end.
Voltage was showing as 25.7v (again no load)

Jason.
 
You could put a resistor in series with the gauge. With your batt discharged to what you reckon is the safe minimum, use a decade box in series to work out the resistance that makes the gauge read empty then wire in that value resistor.

AussieRider.
 
Hi all. I’m back.

The lithium upgrade went well with a range of around 35km on a full charge. But we have a new issue now.

About a week ago, he managed to get it a little wet. Not flooded. But he did get caught in light rain.

Now when starting off there is a bad shudder. Once moving it’s fine. But at the very start of movement there is a shudder.

It’s almost like a bad hall sensor in a brushless motor, but this is a 400W DC brushed motor. So I doubt it’s a hall sensor.

I have had a quick look over and can’t see anything obviously out of place.

Any ideas where else to look ?
Hopefully not a new motor or controller.

Jason.
 
Put a wattmeter or voltmeter on there, and watch for the voltage sag on startup, vs voltage sag during the rest of the usage.

If it's bad enough, the BMS of the pack (if it has one) could be trying to shut off output due to overload, and then when it does the overload goes away, then comes back, repeatedly (shuddering the motor), until finally ti's moving enough to not draw so much current that the BMS keeps trying to protect the cells from the overload.


If that's what is happening, then the battery itself has a problem most likely, usually one or more cell groups that aren't the same as the rest, either weaker or damaged, or with some disconnected cells, etc.
 
G'day DB.
I'd check the motor brushes. Unscrew the brush cap & take out the brush. Does it slide out easily? Could be stuck due to arcing. Are there black marks on the sides? If so, gently clean it with a Scotch Brite & clean black marks in the brass holder so the brush slides easily. Next check the spring for brittleness, blueing from heat & loss of tension.
If the rubbing surface is rough or chipped the commutator may be damaged & 'fraid that may mean a new motor. Repeat for the other brushes. Good to hear the conversion works well.

AussieRider
 
Thanks for the tips.

I’ll be taking a close look at it today and try to see what’s causing it. I’ll start with the motor brushes. As i Suspect that’s the most likely thing, given how new the battery is.

I will report what I find.

Jason.
 
Here’s what I’ve found so far.

Leaning more and more towards motor and or brushes.

Under load, to the point the scooter actually stops moving, (tested on a hill in reverse so worst case scenario) voltage drops to 25.9V. On a fully charged lifep04 ping 24V pack. Pack was resting voltage overnight. So not fresh off the charger. But still fully charged.

When the shuddering happens, the rest of the scooter remains on. So I don’t think it’s the bms shutting off, as it would surely kill the dashboard and all of the buzzers and stuff too ?

And as soon as the scooter is actually moving, it’s fine. Like no noticeable shudder or vibration that wasn’t there when it was new.

Also, when the wheels are off the ground, there is no noticeable shudder either.

Ill pull the motor out tomorrow and inspect it.

Will report back once that’s done.

Jason.
 
Diamondback said:
When the shuddering happens, the rest of the scooter remains on. So I don’t think it’s the bms shutting off, as it would surely kill the dashboard and all of the buzzers and stuff too ?
Click to expand...
Yes, so the pack is not the source of the problem.

(I suggested it because it *is*, in most of the cases of this type of issue, on ebikes/etc., especially when the battery has been changed from the original).


The brushes are a possibility, but I suspect they're ok.

Water ingress into the motor or brushes could compromise them, but if this is like the stuff I've seen, the motor itself is on a transaxle under the body covering, between the rear wheels, and is fairly water-resistant (though it probably can't handle immersion very well).


The next most likely is something in the wiring itself, where things plug together at the motor-to-controller cables. If these are unseated a bit or have oxidation on them, they may carry enough current to operate normally except under higher loads, like startup.

If this is like most of the mobility stuff I've seen, it uses some clone of the Anderson SB50 or PP75 connectors, which both use the same almost-pinky-sized contacts. They are self-cleaning, so if you just power off the system, then unplug and replug all of the power and motor connectors at least once each, it should scrape off oxidation, and also reseat them for full contact.

If there has been poor enough contact long enough, it can heat the connector shell up enough to distort, and then the contacts don't mate properly, and it is a self-increasing problem after that. The shell has to be replaced to fix it, and sometimes the contacts if they have arc-damage.
 
Yeah. The motor is on a transaxle between the rear wheels.
Looks fairly well sealed, though the rubber Boot that seals the motor is not seated properly.

I’ll continue investigation tomorrow. I will plug and unplug all the main power wires going to the controller and motor and see if that fixes anything.

Otherwise I think I’ll pull the motor out and look over the brushes and commutator.

Thanks again everyone for the ideas.

Jason.
 
You probably don't have to pull the motor. Just unscrew the 2 ( or 4 ) black plastic caps to reveal the brushes. With a brush out, you can shine a torch down the holder to check the commutator.

AussieRider
 
I tried to get the rear wheel off today and failed. I don’t have a long enough tool to get enough leverage on the nut. And without the wheel off the motor can’t be removed.

So I’ll have to see if i can get to the brushes without removing it.

There is a black rubber weather proof cap on the back of it.

I’ll keep this thread updated.

Jason.
 
Update.

I spent a few hours today on the scooter.

I pulled the motor and removed the armature and brushes.
There definitely was some wear and dirt.

I polished the commutator and polished the brushes with fine emery paper. Splashed some shellite around also to help clean out the casing and brush housing.

While we had the armature out of the magnet housing, cleaning it, I did spot a very small piece of copper wire that could possibly have been shorting the windings. Though I’m not sure. Removed it anyway.

Re assembled the motor into the scooter and the issue seems to be resolved.

So it was either the brush wear commutator dirty or the copper wire out of place.

Either way it seems to be resolved.

I have sent the importer of the scooter an email asking for the length of a new brush to compare them to. To know how much they have worn in the 2 years and 1500km it’s been ridden.

Thanks again for all those ideas of where to look.

Jason.
C05B1E8A-8E45-4389-846F-312ABF200319.jpeg
 
Hi Guys, ive just found this topic by accident and have joined up hoping to add to discussion of upgrading a mobility scooter to Lipo
Ive been dependant on my scooters for 10+ years and repairs them myself (no such thing as repair shops for these let alone any mechanic skilled in this area)
I am a retired PE so not a complete numpty. I am constantly appalled at the complete rubbish spouted by some people

but I think we got serious helpers here who at least understand ohms law

fyi i requested the admin here if they could put a separate category for mobility scooters as these have a specific set of issues vitally important to users i hope he looks kindly on this as there are no real forum for mobility scooters (worth a damn) and as such they are filled with cowboy salesmen. i suggested to admin that we focus on the technical aspects and not get into "which scooter" discussions - thats already done - badly elsewhere

I notice that you are using Ping batteries, whats your take on them? and their BMS - vitally important

if this topic appears elsewhere pls redirect. :shock:

Robin
 
This is the first ping battery and bms I’ve used in a scooter.
Given it’s fairly low power requirements, it’s been fine.

If we had the money I would have liked to have added the larger AH battery for extra range. But at around 30km or so from the one we got it’s more than enough for his needs.

I’ve used ping batteries and bms in a few low power ebikes over the the years and haven’t had any trouble either.

Jason.
 
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