How fast does pack voltage climb after stopping

[JohnnieB]

Last Spring, just before I upgraded to a 42V pack, when my T-105 batteries were 53 months old, I disconnect the cart from the float charger and let the pack rest for 25 hours. Then I drove it for 10.2 Miles and measured the pack voltage at the various times intervals listed below.

The first reading, the one listed as <1 Minute, was taken after stopping the cart, lifting the seat and attaching the handheld DVM test leads. I didn't measure the time that took, but I'm sure it took no more than a minute, probably less.

Rest time --- Volts ---- SoC
<1 Minute --- 37.05 -- 68.25%
5 Minutes ---- 37.37 -- 76.75%
10 Minutes--- 37.43 -- 78.25%
15 Minutes -- 37.49 -- 80.00%
20 Minutes -- 37.51 -- 80.50%
30 Minutes -- 37.53 -- 81.00%
60 Minutes -- 37.57 -- 82.00%

As you can see, most of the change occurs in the first few minutes and the rate of change progressively reduces as time passes.

When I'm out and about and want to know when it is time to head back to the house and charge the batteries, I usually wait a few minutes before estimating the SoC, but no matter how soon you take the voltage reading, you will know you have at least that much charge remaining.

If the need to know how much charge is left more accurately, wait longer.

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When I do range estimating and other battery testing, I usually wait 30 minutes.

Attached are range estimates using the voltages at the different lengths of time after the cart stopped. As you can see, there is a significant difference.

Only 16.1 miles when I first stopped the cart and 28.3 miles after the pack had rested for an hour.

BTW: At the time, it was a stock 2008 PDS except for 18.3" tires and 2Ga cables, running in Mild-Hill mode, so there was regen braking.

Also, the "L9" batteries (Dec-2009) batteries were 18 months old when I got the cart in Jun-2011 and would only charge to 85% SoC. After nearly two years of TLC, they were holding 102% SoC after 25 hours of rest.

Nothing other than distilled water was added to the batteries. The gain was pure charging techniques using off-the shelf chargers.

[Knothead]

Originally Posted by JohnnieB

Nothing other than distilled water was added to the batteries. The gain was pure charging techniques using off-the shelf chargers.

Yeah, but you have the tin-foil hat!!

[Mancebo]

Johnnie,
Just the information I was looking for. Thank you.

I have had the cart since last summer and have not had to put any water in the batteries. Is that good or bad?

You mention bringing your original batteries back from grave, where you putting water each time you check the batteries (assuming they needed them)?

[Volt_Ampere]

That is the typical behavior of FLA batteries. I forget the physics of this (I used to know). We used to use Amp-hour meters in the electric cars I worked with back in the 70's to keep track of how much capacity was used and how much was left. Not any more accurate than the voltage reading since the capacity used has to do with discharge current profile and not just straight amp-hours.

[JohnnieB]

Originally Posted by Mancebo

Johnnie,
Just the information I was looking for. Thank you.

1. I have had the cart since last summer and have not had to put any water in the batteries. Is that good or bad?

2. You mention bringing your original batteries back from grave, where you putting water each time you check the batteries (assuming they needed them)?

1. It's not completely good or completely bad. FLA (Flooded Lead-Acid) batteries usually use some water during the normal discharge and recharge cycling. How much they use depends on numerous factors.

Indianapolis is relatively humid and cool, so water loss due to evaporation probably wouldn't have been very high. Based on information in your other posts, you were using a low current charging system, so there probably wouldn't have been much water loss due to electrolysis (gassing) either.

Now that you are using a DPI charger, you'll probably see some water usage.

2. While I was doing multiple back-to-back charges and driving short distance and recharging to resurrect some batteries that had been poorly maintained by the previous owner (a golf course in Arizona), they gassed a lot, so they used quite a bit of water.

I checked the electrolyte level about once a week and usually needed to add water. IIRC, I added upwards of a gallon of distilled water in the two months I was charging the living daylights out of them. The max SoC had climbed from 85% to 94%, which I figured was all I was going to get and was happy that I had gotten that much improvement, so I retired the Powerwise II I was using and switched to a Protech charger that float charged after the regular cycle completed. By the next spring, those batteries were charging to 98% SoC.

The Protech charger failed and was replaced with a DPI and by the time I replaced the 36V pack for a 42V pack, the T-105 batteries that came with my cart were charging to 100% SoC.

Of course, SoC does not equate to storage capacity. All I managed to do was get the batteries to accept a 100% charge of whatever the storage capacity of the abused batteries was. However, 100% of the reduced storage capacity is better than 85% of the reduced storage capacity.

[Mancebo]

Understood... So now I am nervous and will check on the weekend. I haven't had to put any water in (since acquisition). But I haven't checked since the weekend before April 1st, based on recommendations I have been checking monthly.

But now I am armed with more knowledge from you, UroGator and Scottyb. And I have my nice shiney DVM to look at. Exciting times ahead!!!!

[JohnnieB]

Originally Posted by Volt_Ampere

That is the typical behavior of FLA batteries. I forget the physics of this (I used to know). We used to use Amp-hour meters in the electric cars I worked with back in the 70's to keep track of how much capacity was used and how much was left. Not any more accurate than the voltage reading since the capacity used has to do with discharge current profile and not just straight amp-hours.

Back in the same era, the hospital I was working at had robotic carts that delivered food trays and supplies. I never got involved with the battery packs and drive systems very much, but I did learn a few new swear words from the guys that did.

The carts had removable FLA battery pack modules that tracked Watt-Hours and the cart automatically drove itself to the maintenance shop when the battery pack said it needed to be replaced with a charged one. Nice concept, too bad it didn't work very well in the real world.

In the 90's I got superficially involved with another robotic delivery system that used roughly the same WH counting concept, but with better computers and NiCd batteries, it worked fairly well.

[Volt_Ampere]

If usage is fairly consistent, then the WH meters work ok to predict how "full" your pack is. It runs backwards when you charge. We used to keep real good records on our cars when I was working on them during my masters program in school. I learned more working on electric cars than from all of my other courses combined! I've now forgotten some of it to make room for the modern EE stuff.

[scottyb]

" he carts had removable FLA battery pack modules that tracked Watt-Hours and the cart automatically drove itself to the maintenance shop when the battery pack said it needed to be replaced with a charged one. Nice concept, too bad it didn't work very well "
I love it - I picture a line up of battery hungry carts lined up just bumping and shoving at the maintenance shop doorway and maintenance workers running around pulling hair and cursing

[JohnnieB]

Originally Posted by Volt_Ampere

If usage is fairly consistent, then the WH meters work ok to predict how "full" your pack is. It runs backwards when you charge. We used to keep real good records on our cars when I was working on them during my masters program in school. I learned more working on electric cars than from all of my other courses combined! I've now forgotten some of it to make room for the modern EE stuff.

I learned some new stuff and relearned other stuff since I've owned a golf cart.

I didn't get into the batteries and drive system very much, I just got called in on the guidance system occasionally. The carts followed a wire buried in the floors with a signal on it.

The battery pack module had two boards with an Intel 4004 (4 bit computer) IC on them and the guidance system had four boards with the same CPU chip. After I moved on, the carts were upgraded with boards the had 8008 processors and they worked better, but still had a bad habit of stalling in the most difficult places to retrieve at the most inopportune times.

Originally Posted by scottyb

" he carts had removable FLA battery pack modules that tracked Watt-Hours and the cart automatically drove itself to the maintenance shop when the battery pack said it needed to be replaced with a charged one. Nice concept, too bad it didn't work very well "
I love it - I picture a line up of battery hungry carts lined up just bumping and shoving at the maintenance shop doorway and maintenance workers running around pulling hair and cursing

It was worse than that. The carts had their own elevators and when too many carts lined up for a battery pack change, or a cart died on an elevator, they started lining up on the patient floors also.

Fortunately, the designers got most of the kinks out of the concept when I ran across another robotic delivery system in the 90's. That one had an Autocad map of the facility stored in memory and used regular people elevators, so it would go to a different elevator if the one it called didn't show up within a preset time limit.