Excessive Voltage Draw, 96 txt

[haligen]

So I'm going to take the kids to the park the other day, leave with a fully charged pack (38.8 ), and I make it a block and a half when my digital battery meter goes from showing 33ish volts to 20ish volts (while running) and the cart slows considerably. Then when I stop and try to start again the meter is showing 17ish volts and the cart barely creeps forward. I get off and push the cart and manage to get it creeped back to the house. I let it sit a while and look at the meter and it rested back at 38.6v. What could possibly be causing the excessive draw? Bad motor? The batteries are one year old US batts and I'm the original purchaser. They are wired with quality 4g. The cart has never been run below about 80%. The fluids are good on the batts and I always place the cart on charge when done. There are no lights or accessories hooked the the pack. Any starting point would be great.

[scottyb]

You have some bad batteries that are dropping a cell under load. As the internal connections between the cells age they become weak. Eventually they are only strong enough to show full voltage at rest but cannot sustain delivery under load.

[JohnnieB]

If it was something other than battery pack failure, you'd probably smell smoke.

To find out which battery or batteries are bad, do this:
Measure and record the six individual battery voltages.
Drive cart until it slows down, then measure and record the six individual battery voltages again.
The one or ones that dropped considerably more than the others are bad.

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US Battery is one of the better names in cart batteries, but batteries from all manufactures have failures.

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Sounds like you have an excellent battery charging/maintenance program, but you didn't specifically mention it, so I gotta ask.
You've always filled the batteries with distilled water haven't you?

[haligen]

Dang, batteries it is. I need to check the date codes again but I think I'm a few months out of warranty, go figure. JohnnieB, I've always used distilled water. Even have an excel sheet from when I got the pack and did the initial break in logging the charged and discharged values lol. I"ll try and get the cart out in the next few days and report back with what I find. Thanks for the help.

[JohnnieB]

Glad to hear the you've only added distilled water to the batteries.

I re-read your first post and noticed you said: "The cart has never been run below about 80%."

I'm more attuned to thinking in SoC (State of Charge) terms than DoD (Depth of Discharge) terms, so it didn't wave a red flag the first time I read it.

Discharging to 80% DoD (which equates to 20% SoC) is consistent with the maximum discharge suggested by many battery manufacturers, but they are in the business of selling batteries. Around here, we recommend that golf cart batteries never be discharged more the 50%.

In general terms, the higher the average SoC (Reciprocal of DoD) that is maintained, the longer the batteries last.
Here is a chart showing estimated Discharge/Recharge cycles for US Batteries based on DoD.

Basically, a new battery has a limited number of charge cycles and the deeper it is discharged, the faster they are used.
For example, if playing 18 holes of golf is on cycle, playing 36 holes without recharging in between, uses 3 cycles rather than just two.

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BTW - What charger are you using?


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[haligen]

I was speaking in terms of SoC. The pack has never been allowed to be below 37.5v. In fact I doubt it has ever really seen below 38v. I bought the batteries while I was still working on the cart so we haven't really used the cart all that much. My charger, its a powerwise like the one in this pic.

[JohnnieB]

I was looking for a reason why your battery pack failed prematurely and you appear to be doing everything right, so I was grasping at straws.

The Powerwise 28115 charger is a good one, so that more or less narrows the possibilities down to environmental and manufacturing issues.

[haligen]

Starting Volts
6.34v
6.33v
6.39v
6.30v
6.31v
6.36v

Rode about a block and it was drawing down hard, 17 to 19v while moving. stopped and this was the first check
4.34v
6.1v
6.22v
5.3v
6.15v
5.84v

Immediately after checking the 6th battery I rechecked.
5.74v
6.17v
6.28v
5.39v
6.19v
5.88v

So is it just the 1st battery or do I have a couple crudding out?

[JohnnieB]

Originally Posted by haligen

Rode about a block and it was drawing down hard, 17 to 19v while moving. stopped and this was the first check
4.34v
6.1v
6.22v
5.3v
6.15v
5.84v

So is it just the 1st battery or do I have a couple crudding out?

My guess is that one is bad , one might be bad and another is iffy.

Has the cart sit for any appreciably length of time without being ridden?

[haligen]

The longest it sat without being used might be a month at the most. We started using the cart about July and were pretty steady about 4 or 5 times a week till about November. Then it got a little to cold to ride so it sat most of December. I would walk out about once a week or so and unplug/replug the charger. It didn't really start acting up till late February and was a once in a while thing till now.