DIY Lithium Ion 56 Volt Golf Cart Battery Conversion

Lloyd-ss

Active Member
Darn, you guys can be rough of each other! ;)

So, just had the first failure on the Li Ion conversion. poop. But not too bad. The on-board battery charger crapped out.
The charger was a cheap 56v 5A for about $60. It had always worked perfectly, but it just died. Wouldn't light up at all. So I took it out and opened it up and found a bunch of dead stink bugs in it. One was missing its head and I could see a spot of burned bug guts inside the box. There were 2 surface mount resistors that were obviously burned out so I soldered in a couple of axial style replacements. The problem was that on one of the resitors I could only read the last digit, so I did the only logical thing and guessed at the first 2 digits. I soldered in the replacements and was pretty pleased with the way it looked. I plugged it in and POW, a flash, smoke, the top of a capacitor shot off, and generally a mess. That would certainly have wiped out the entire colony of stink bugs.
So I just ordered another cheap charger, but it is black friday on amazon so instead of $60, this one is only $43. YEA! Probably should have ordered 2. I had to stick with the same type of charger so that it will fit into the space where the old one did. Supposed to be here Monday. I will check for more stink bugs with the shop vac. I am going to blame the failure on them.

StinkBugs.jpg
 

Lloyd-ss

Active Member
I hope everyone is doing ok these days.
The lithium ion conversion now has 13 months on it and 282 miles and I am still pleased with it. The cart is driven 5 or 6 days a week and is charged every week or 2.

There is no BMS on this system and at he beginning I was wondering if there would be any problem with the Li cells staying balanced, that is, all keeping approximately the same voltage thru all the charging cycles The system has 7 modules, for a total of 14 cells, with a nominal voltage of about 4 volts per cell. I carefully watch the system voltage on the "Cycle Analyst" to try and spot if anything odd is happening. I recently checked the voltage on all 14 of the cells after they were charged. The voltage varied from 3.989 volts to 4.005 volts for a spread of only 0.016 volts (16 millivolts). That is totally in the acceptable range and I didn't need the expense and complexity of a BMS.

During the 13 months, I have made 3 fixes/changes. One was replacing the cheap battery charger with a cheaper ($43) one. The second one is still holding up fine but ocasssionally the fan squeaks on startup. If I unplug the charger a few times the squeak stops. The second thing was replacing the 0-5k rotary throttle pot with a linear pot. I wasn't happy with the original pot linkage and the linear pot was a lot easier to get a nice smooth resistance output from. The third fix as a loose screw on a wire in the reverse control circuit. It manifested itself as a herky-jerky motion in reverse. Tightening the screw made it all better.

But I do have a curious problem that I need to get some expert advice on.:rolleyes:
Before I did the Li conversion I changed out the motor to a High Torque model 42A from D & D motors. It has worked fine, I guess. but not having any golf cart experience I really don't know for sure. Here are symptoms. There is a 300 yard long steep hill on my property. When climbing this hill at full throttle, most of the time everything is fine. But sometimes, part way up the hill I get what feels like a bad carburetor bog. We all remember those, right? When it bogs, the amps drop from about 110 down to 40 or so. If I let off on the throttle and try again, it usually takes off again at 110 amps. I think it happens more during hot weather, but am not sure. I have stopped when this happened and felt the controller and cables, etc, and nothing was even warm!
Now here is the kicker. The controller is only an SPM225. I have it programmed to a fairly mild speed and torque curve, but I know something is wrong. The controller was new and I don't think it had this problem originally. Even though I have the controller programmed to 200 amps max, the amps never go above 150 on the voltagedisplay. I know the battery pack can deliver a lot more than 150A. I am wondering if the controller is just too small? I bought it because it was new, and really cheap, wondering if it was big enough for the task
Other than the full throttle bog, and not drawing as many amps as I think it could/should, it works fine. Does anybody have a suggestion on what I could check or do?
Thanks in advance, Lloyd
 
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Diode

Cartaholic - V.I.P. Sponsor
Hook a laptop to the controller keep an eye on your throttle percentage your voltage and your current let's see if you notice anything with those three
 

Lloyd-ss

Active Member
Thanks. I saw that feature of real-time monitoring in the Alltrax toolkit but have never tried it. Sometimes you have to be forced into learning something new, LOL. Its fairly easy to force the bog to occur, and hopefully a blip of some kind will be visible when the bog occurs.
 

Diode

Cartaholic - V.I.P. Sponsor
It could just be your throttle curve setting try a linear throttle see if that changes anything
 

Lloyd-ss

Active Member
I hooked the laptop to the controller yesterday and had a real hard time making the cart bog down. It did it once but the sun was too bright on the laptop for me to read anything.
Then, in the options, I checked the box the said lock throttle options, keep linearized throttle (or something like that). The box had been previously un-checked.
I fully charged the cart today (55 volts) and again, could not cause it to bog. This was at dusk and I could read the laptop screen. Then I noticed the save to file option, and turned that on. Made a downhill and uphill run and still no failure. But it did record 1400 lines of data in a CSV file in four minutes.
The data was interesting...and normal, I guess.

It hasn't been super hot here the past few days and that might have something to do with it not failing, and I don't see any 90+ temps in the near forecast. I will try it again tomorrow.
I wonder if the check box for the linearized throttle had anything to do with it like you suggested? I thought I could create the failure easily, but that's Murphy's law.
 

Lloyd-ss

Active Member
Just took it for a spin and got 2 failures in one run..... and got the monitor data saved in a csv file.
First failure. Accelerating at WOT up the hill. Data sample rate appears to be 6 times per second.
The good readings before the failure were Throttle 89%, Batt volt 54.4, Batt current 44.8, Motor volt 41.7, Motor current 58.4, M- temp 35.1, Global shutdown 0, Throttle position 3671, Throttle pointer 3666.
Then when the failure occurred (for about 1/3 of a second) Batt current dropped to -.4, Mot volt dropped to 8.1, Mot current dropped to -2.8, Global shutdown flag stayed at 0, Throttle position stayed at 3671, BUT Throttle pointer dropped to 537.
The second failure, about 4 seconds later (for about 1/6 second) showed similar readings except that the Global shutdown flag also changed from 0 to 1.

After the very brief failures everything went back to normal and the cart kept going just fine.
So, the Throttle Pointer is showing something during both failures, and the Global shutdown is showing something in one of the 2 failures.
Any ideas, or do I call Alltrax for a diagnosis?
Thanks for helping me out.
Lloyd
 

Diode

Cartaholic - V.I.P. Sponsor
Unfortunately Monday's a holiday you could send an email and attach your files
 

Lloyd-ss

Active Member
I heard back from Alltrax the other day and they said that it was most likely a connection problem at the motor or F-R relay, or an internal fault with the controller. So I gave all the connections in the system a thorough going over and tried it again. Crap. Problem still there. So I got to thinking some more and I have 3 DPDT low voltage relays as safety interlocks so you can't go from F to R or R to F without pressing the brake pedal all the way down. So I swapped those 3 relays around (they are in socket mounts) to see if it made any difference. Different poles are used in the different relays and I was hoping that if one of the contacts was fried, maybe a different relay might not use that same set of contacts. Well, it did seem to fix the problem but performance was still kind of anemic. I had also noted on the monitor file from the laptop that full throttle was only showing about 4000 ohms instead of the 5000 that it checked with an ohm meter. That had seemed suspicious.
So, I did a "Reset to Factory Defaults," and what do you know? :bonk: That seemed to give the full power performance back. I had to adjust a couple of the parameters to tame the beast a little bit, but I hope I am not the only one who has done this sort of thing..... over-thinking the problem.
Try the simple stuff first, LOL.
And I put the 3 low voltage relays back into their original locations to see if they had been a real problem at all.
I have my fingers crossed that it all stays good.
 
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