High voltage with T5 controller

I installed two volt 12s packs in series to get a hot rod gem. When first installed, had pack voltage of 94.9 total. Got code 16 on dash (overvoltage). Installed 15v spoof on pin 1 and everything works as it should.
WOW, should have done this upgrade earlier! Quicker off the line, higher top speed and it seems like less heat on motor. Took 260+ pounds of batteries out, so I increased overall payload as well.
Now for the BAD news, looks like the T5 controller doesn’t like the voltage like the motor does. After initial install and a lot of test driving I plugged in the new deltaQ charger I ordered from Dave with 177 profile installed. Shut off charger at 99V pack voltage, settled to 98.8V resting. Got code 16. Two hours with bright headlights dropped pack voltage to 98.2. Measured 83,2V after spoof. Still code 16.
Installed my second 48s string showing 94.9V, hooked up to them and cart works properly again.
My guess is HVC (high voltage cutoff) for T5 is 80V.
Is there anyway to change this setting? Is there a 20v spoof? I don’t mind limiting charge to <95v. I’m sure it would help cell life.
Other question is how do I properly connect my two 48s pack in parallel to double my range and not my voltage? I started hooking everything up and I’m pretty sure I’m confused. Got it working with just two packs in series, but unclear on how to make the parallel connections for the other two packs. I have a couple of Dave’s harnesses but it doesn’t make sense that those would be the only connections between the modules. Shouldn’t there be a heavy gauge wire (battery lead) connecting them as well?
Thank you for guiding the newby along. I think I’m seeing some light in this project!

I don’t know how the T5 reacts to HV. The cutoff needs to be 84v or more to work with lead, so it shouldn’t need a higher voltage spoof.
Can’t find a drawing at the moment.
To parallel with another 24s connect the other two in series as you did the first. Plus to minus.
Then you have two 88v batteries.
Set them side by side and connect minus to minus with heavy wire.
Then test with a meter between the two 88v batteries from plus of one to plus of the other.
It needs to be zero volts to proceed. If zero, connect them with a power cable.
Next test between the 2 neutrals. (neutrals are the 44v series connections) Again needs to be zero volts to connect them safely with heavy gauge.

The point being, never connect two points unless you measure zero volts.

You now have an 88v 100ah battery.
Load connects inverse parallel. Ie. plus from one set and minus from the other.
It will work with both leads from one pack, but is not technically correct.

This is another way. I found a picture. Electrically same result.
It might work better if you have a parallel set on each side and a single series connection.

1 and 2 are the low side batteries. Connect together with the low bms plug.
3 and 4 connect together to high bms plug.

Thank you, That makes sense.
Not sure why my controller is acting this way. I thought it should take up to at least 86 volts as well. I measure 83.2 at pin one after the spoof and get code 16. When it drops to 79.9, I’m good to go. Will be playing with it later today. I’ll get some pix as well.

If you have an electronics store near you, pick up 10 3a diodes. 1a for a test.
@dougl is doing that in another thread. Each diode adds about .6 volts. (less)
I can send you a 5v add-on if you want.
Keep an eye on main contactor for overheating. >90v is a lot for a 70v coil.
Also the heater. Heater will work very well for about 1 minute.

I was going to go for 4.1V/cell too but was told that even that is a bit high and will shorten the life of the batteries. So I’m going for 4.0 on my 22S system. Maybe even 3.95 just to play it safe since there’s tons of power and capacity in these batteries compared to the Pb batteries.

I had put 5 1n4004( 1A diodes ) in series to drop my voltage but as soon as I powered things up the solder on the diodes melted. So my T1 pulls well over 1A and I suspect it’s more like 2A with a bit more inrush on startup. These might work and if a single row of them gets too warm, add a second string of them to split the load.

Measure if you get time. That seems way too high.

Ya, I have to find one of my meters which I’ve not blown the 10A fuse yet. LOL

@Inwo so I saw a spark when I connected the meter so there was some capacitance charging happening but the digital meter didn’t catch the peek. Runs at ~.150a when OFF and 1.2A when ON.

So the 3A diodes should do fine.

Now I need to check mine. No way my spoof will handle an amp.
15v * 1a is 15 watts. Holy smokes.
15v * 250ma is 375mw. Even that will melt the shrink tube.
What is different about your controller wiring than normal?

I’ll try to get to an electronics store soon, but I’m lost in those places.
Would be much easier for me if you’d send another 5V spoof so I can verify that is my issue. Also would like a momentary switch to be able to bypass spoof on low voltage starts if you had one available. Let me know price and I’ll get you paid through PayPal. Shipping to 92648. Thank you. Bill

Send $25, Ill make something up. Need a 5’ lead to switch?

Yes, that should be more than adequate to place switch in hidden area. Will pp shortly. Thank you.

Pp sent. Thanks again for your knowledge and assistance. May put something together with grant on those Fontana modules


Good deal. The two of you could make sparks fly.
How could you get them to Grant? Meet half way?
Maybe the two of you could make enough money to do a Bolt pack. :slight_smile:

If you want to go crazy, I think this would fit, and my harness does 3p.

150ah. That’s Bolt range.

Holy cow, you’re fast!
Looks easy when I see your picture. Not so easy for me in the Frye’s aisle!
The 5V spoof would go in line with the 15 to get 20 correct?
Want to look more into why my HVC is 80v and not 84-86 which would make more sense if using Pb. I had factory gel batteries with proper date codes so I would think I’d have same limits as any other gem. Doesn’t look like anybody’s molested this one but me, all factory inspections paint marks are (were) intact, so pretty sure all factory settings. My gem manual doesn’t specify HVC level and I can’t find anything elsewhere besides the 86v number. I have a 2014 E4 with the T5 controller If it makes a difference.
I noticed in your earlier posts the spoof required 3 wires. No now only one. What were the other two? What could help with contactor coil life? Does the car sense voltage elsewhere? Everything seems pretty straightforward but what do I know?
Thanks again for your insight

See what I mean about fast!
Yes, sparks (and GEMs) could fly!
If all works in a perfect world we can lock in the GEM lithium upgrade market! All 6 of them!
Should see a good market for drop in, plug and play modules, but there has to be a reason nobody is doing them. Liability? The big L kills a lot of start ups here in California. Welcome to the “sue you” state!
Or everybody who is willing is DIY and not willing to pay for anything.
Either way I’m a rebel and have to do things my way to learn. I think we’re kindred spirits in that regard.
I am extremely grateful that I am learning a lot through your posts. I’m just bummed the older posts don’t have pix attached anymore. I’m a very visual learner!
Thank you again!