under-load voltage abnormally low (1.61v per cell)

[sportcoupe]

I got a 72v lifted series cart with Alltrax and PQ torque motor on 24" low pressure tires. It has 2011 batteries and a couple 2013's. High current cables look rough. Yesterday I took it out in my subdivision (flat paved roads) with a full charge and two very healthy sized men (no horse jockeys here) including the driver. Within 3 miles the under load voltage dropped substantially to 58v (72v cart) and speed slowed considerably. That's 1.61v per cell which is below the normal 1.75v as recommended from the manufacture.

The battery setup is 9-8v 121Ah US Battery (8VGCE XE) and each passes a cheap handheld load check more or less. My SoC after 12 hours rest is 75.6v and I noticed the charger cuts off around 88-89v. Is that too low for US Batteries?

Here are individual SoC readings after 12h off charge. Batts #5 and #6 are 2013, the rest are 2011.

1) 8.38
2) 8.36
3) 8.35
4) 8.38
5) 8.52
6) 8.52
7) 8.37
8) 8.31
9) 8.41

I plan to do a load check using the cart at some trails nearby and will record the numbers. The extremely low 58v under-load reading I saw concerns me after such a short drive. Can a bad high current cable cause that?

[scottyb]

2.4v should be enough of a max charging voltage. Sounds like the batteries are not holding the amperage. Can you do individual live load tests with the cart on a hill or loaded up?

[radioman]

A bad cable connection on a battery post could cause this. You didn't mention if you checked the voltage of each cell when the battery voltage dropped to 58v.

[sportcoupe]

Is 2.4v per cell high enough for US batteries? I have a Delta Q charger and it is supposed to have programmable charge profiles.

Yes I intend on load checking per battery on some trails I have locally today. I will post back.

Yesterday when I saw the low under-load voltage I didn't have my meter with me to check per battery. I will today.

[sportcoupe]

With the charged pack from yesterday I drove to a place I can do a bunch of stop and go testing. It's still flat but it's all I got. Here are the static readings and under load readings. I didn't give them any recover time.

1) 8.16 --- 5.35
2) 8.13 --- 5.25
3) 8.13 --- 4.56
4) 8.13 --- 4.93
5) 8.32 --- 5.56
6) 8.32 --- 5.96
7) 8.15 --- 5.37
8) 8.00 --- 3.73
9) 8.15 --- 4.56

Under load volts are extremely hard to take I found out. My digital voltmeter changes so fast and I have to keep an eye on the road at same time.

Seems battery #8 is far below the rest. I'm starting to doubt it could be the battery cables now even though they don't look too good.

[Volt_Ampere]

Your battery #8 is clearly bad. There is a lot of variation in the others too. A DVM is not very good at reading the load voltages though.

[JohnnieB]

A 72V pack and 121AH 8V batteries aren't on any of my spreadsheets yet, but for starters:
1. The finish charge for a US Battery should be 2.55V +/- 0.05V (91.8V)
2. 100% Soc for US Battery is 2.33VPC, so a fully charged 72V pack (36 cells) should be 83.88V
3. 1.61VPC is below the 1.75VPC that manufactures stop at when the do non-destructive testing, but above the 1.56VPC where plate damage starts occurring.
4. Bad cables tend to reduce Amp flow rather than increasing it.

First glance: It looks like the batteries are not being fully charged.


I'll be back. After I do some number crunching.

[sportcoupe]

Charger is Delta Q model 912-7200 with profile 1 set as default. I cannot find info on the other pre-loaded charge profiles anywhere. Looks like a call Monday is in order.

[JohnnieB]

For whatever reason, your batteries are not being fully charged.
Battery #8 may be bad, but it might be recoverable.

1 ) 8.38 = 86%
2 ) 8.36 = 84%
3 ) 8.35 = 83%
4 ) 8.38 = 86%
5 ) 8.52 = 99%
6 ) 8.52 = 99%
7 ) 8.37 = 85%
8 ) 8.31 = 78%
9 ) 8.41 = 90%

Pack = 75.6V = 88.5% Soc

When you started your individual battery load test, the pack was at 73.49V or 60% SoC.

Attached is a SoC vs Voltage chart for US Battery batteries. It doesn't have 72V on it, but it does have VPC, so just multiply VPC by 36 to get 72V.

Also attached are the charging instructions from US Battery.
My guess is that the three stage charging instructions is what Delta Q uses.

[JohnnieB]

Originally Posted by sportcoupe

Charger is Delta Q model 912-7200 with profile 1 set as default. I cannot find info on the other pre-loaded charge profiles anywhere. Looks like a call Monday is in order.

Algorithm #1 Is for T105.
Here are two users manuals that include 912-7200, but were printed in different years and give different #'s for US Battery (4 and 11). so it is phone time.