Load tested my US batteries- here are results

[Conradconrad]

So I have 7 new (as of December 201 US2200 6V batteries. During a throttle issue JohnnieB noticed I have a pretty good voltage drop under load(acceleration) so I finally got around to load testing each battery.

My starting voltage maybe 10 minutes off the charger was about 45.9
I drove the cart about 2 miles to deplete the surface charge.

Being in flat south Florida I am lucky enough to have a small waterway canal bridge near by that is quite steep on one side. I figured if I am able to come to be in the foot of the steep section and press the accelerator full throttle that should give a decent load on the batteries.

I bought a Fluke 110 plus and also bought push on alligator clips for the probes

The waterway bridge runs were interesting. I was parked on one side, then would pull into the street at the foot of the steep section, full acceleration over the bridge, go down, do a u turn. Then I would quickly reset the Min on the Fluke and from a full stop, 100% accelerate over the bridge to the other side.

Then I would record both measurements for that battery while having a timer. I would let the pack rest a out 6.5-7 minutes before doing the same thing over again. Below are the results- run1is up one side of the bridge followed by a u turn and immediately back over the bridge again - run2


Battery 1- Run1: 5.301 Run2:5.293

Battery 2- Run1: 5.291 Run2:5.259

Battery 3- Run1: 5.287 Run2:5.236

Battery 4- Run1: 5.284 Run2:5.271

Battery 5- Run1: 5.215 Run2:5.199

Battery 6- Run1: 5.222 Run2:5.211

Battery 7- Run1: 5.183 Run2:5.178

Distance was about 0.205 miles to complete each bridge loop per battery.

Then I let the pack rest while I looked at the numbers and took it for a long distance spin. I drove another 6.9 miles with mostly a long stretch of open road with several stop and goes. Coming back right before the home on the same bridge I was able to record a minimum pack voltage of 34.37v from a complete stop to full acceleration on the steep section.

About a quarter mile down the road I parked the cart and the voltage right away was 44.43v and after an hour of sitting it is at 44.83V

I believe my batteries are a bit weak ? I am surprised that after about 10.5 miles of driving and letting the pack rest for an hour the voltage is back at 44.83V?

I am using a DPI charger

[Conradconrad]

After I wrote this up I measured the individual battery voltages:
Battery 1- 6.416

Battery 2- 6.416

Battery 3- 6.409

Battery 4- 6.408

Battery 5- 6.410

Battery 6- 6.415

Battery 7- 6.406

Total 44.88v after 1hr 25 minutes
How can I drive 10.5 miles and still be at 100% state of charge capacity but yet loose voltage under load as distance accumulates?

[JohnnieB]

Originally Posted by Conradconrad

Total 44.88v after 1hr 25 minutes
How can I drive 10.5 miles and still be at 100% state of charge capacity but yet loose voltage under load as distance accumulates?

Every time you lift your throttle pedal up, you get regen braking, which puts amps back into the batteries. You made 14 trips across the bridge and if you were WOT on the uphill legs and pedal up on the downhill legs, you recovered anywhere from about 15% up to around 50% of the amps used on the uphill legs during the downhill legs. Same is true when you coast a bit before applying the mechanical brakes when coming to a stop.

Voltage loss under load increasing as distance accumulates is due to the battery voltage not having time to fully recover between trips across the bridge.

In simplistic terms, electricity is produced by a chemical reaction between Lead and Sulfuric Acid and the higher the concentration the acid is, the higher the voltage. A sulfate ion from the Sulfuric Acid joins with the Lead to form Lead Sulfate and electricity is produced. As sulfate ions are transferred to the Lead, the Sulfuric Acid becomes water and the Lead becomes Lead Sulfate, neither of which can produce electricity. Of course, that is at the molecular level and there are billions of molecules in the gallon and a half of Acid and couple square feet of Lead surfaces inside the battery.

The net result is the Acid in intimate contact with the Lead surfaces becomes less concentrated, so the battery voltage decreases. Given time or agitation, the higher acid concentration that has not yet been in a chemical reaction migrates into intimate contact with the lead that has not yet been transformed into lead sulfate and the battery voltage climbs to whatever the newly arrived acid concentration is.

In other words the electrolyte stratifies horizontally. (Stratify refers to vertical layers and if there is a term for that happening horizontally, I haven't found it.)

---------------
How far the battery voltage drops depends on how many amps are being drawn. Unfortunately, I don't know how many V/100A a US2200 drops, nor do I know how many amps when being drawn going up the hills, so I don't know if your batteries are weak or not, but they do seem to be dropping a lot.

[Conradconrad]

Originally Posted by JohnnieB

Every time you lift your throttle pedal up, you get regen braking, which puts amps back into the batteries. You made 14 trips across the bridge and if you were WOT on the uphill legs and pedal up on the downhill legs, you recovered anywhere from about 15% up to around 50% of the amps used on the uphill legs during the downhill legs. Same is true when you coast a bit before applying the mechanical brakes when coming to a stop.

Voltage loss under load increasing as distance accumulates is due to the battery voltage not having time to fully recover between trips across the bridge.

In simplistic terms, electricity is produced by a chemical reaction between Lead and Sulfuric Acid and the higher the concentration the acid is, the higher the voltage. A sulfate ion from the Sulfuric Acid joins with the Lead to form Lead Sulfate and electricity is produced. As sulfate ions are transferred to the Lead, the Sulfuric Acid becomes water and the Lead becomes Lead Sulfate, neither of which can produce electricity. Of course, that is at the molecular level and there are billions of molecules in the gallon and a half of Acid and couple square feet of Lead surfaces inside the battery.

The net result is the Acid in intimate contact with the Lead surfaces becomes less concentrated, so the battery voltage decreases. Given time or agitation, the higher acid concentration that has not yet been in a chemical reaction migrates into intimate contact with the lead that has not yet been transformed into lead sulfate and the battery voltage climbs to whatever the newly arrived acid concentration is.

In other words the electrolyte stratifies horizontally. (Stratify refers to vertical layers and if there is a term for that happening horizontally, I haven't found it.)

---------------
How far the battery voltage drops depends on how many amps are being drawn. Unfortunately, I don't know how many V/100A a US2200 drops, nor do I know how many amps when being drawn going up the hills, so I don't know if your batteries are weak or not, but they do seem to be dropping a lot.

Could the dropping be due to charging incorrectly? I have the dpi charger and misread that US batteries were profile #4 and charged the batteries on that from December until April and then when I was cleaning out the garage I looked at the back of the charger and saw US batteries is profile#1 and then changed it to the correct profile and have charged that way since.

I also know we really have not driven the cart more than 4-5 miles since December before plugging back in, would driving further on a charged cart expand the volume of the battery?

I can record a log on Sunday with the laptop to get an idea of the volts/100amps ratio.

What else should I look for to improve the voltage drop?

[JohnnieB]

Originally Posted by Conradconrad

1. Could the dropping be due to charging incorrectly? I have the dpi charger and misread that US batteries were profile #4 and charged the batteries on that from December until April and then when I was cleaning out the garage I looked at the back of the charger and saw US batteries is profile#1 and then changed it to the correct profile and have charged that way since.

2. I also know we really have not driven the cart more than 4-5 miles since December before plugging back in, would driving further on a charged cart expand the volume of the battery?

3. I can record a log on Sunday with the laptop to get an idea of the volts/100amps ratio.

4. What else should I look for to improve the voltage drop?

1. Yes. Depending on charger age, #4 was either AGM (older chargers) or Crown (Newer Gen-III DPI chargers).

2. How many charge cycles have the batteries had? If less than 2 dozen or so, they may not be fully broken in yet.

3. Record a log, plus check the individual batteries under load. The voltage drop of the pack also has the voltage drop of the high current cables connecting them in series for 42V. Put F/R in R for a few seconds before each uphill run to mark starting points. Then we get the max battery amps for the run on the log and the min battery voltage on the DVM.

4. Do some back-to-back charges. (Unplug DPI from cart while it is float charging, wait a minute or two and reconnect. Or take cart on short drive around the yard and plug back in.) I got a 36V set of T-105 batteries that would only charge to 85% SoC up to 95% in a few weeks doing that two or three times a day, or thereabouts. I ended up getting another year's use out of them.

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Maybe US Battery can provide some V/100A data for the US2200 batteries.

After we find out how much they drop vs how many Amps are being drawn, one of us should contact USB tech support.

Attached is a USB Tech service bulletin about chronically undercharged batteries. You need to verify the DPI is reaching at least 52.5V (2.5VPC x 21 cells) before the regular charge cycle ends and it goes into float charge. Since your DVM has a MIN function, it probably has a MAX function, so just connect it to the battery pack's main terminals and let it do the watching for you.

[Conradconrad]

Originally Posted by JohnnieB

1. Yes. Depending on charger age, #4 was either AGM (older chargers) or Crown (Newer Gen-III DPI chargers).

2. How many charge cycles have the batteries had? If less than 2 dozen or so, they may not be fully broken in yet.

3. Record a log, plus check the individual batteries under load. The voltage drop of the pack also has the voltage drop of the high current cables connecting them in series for 42V. Put F/R in R for a few seconds before each uphill run to mark starting points. Then we get the max battery amps for the run on the log and the min battery voltage on the DVM.

4. Do some back-to-back charges. (Unplug DPI from cart while it is float charging, wait a minute or two and reconnect. Or take cart on short drive around the yard and plug back in.) I got a 36V set of T-105 batteries that would only charge to 85% SoC up to 95% in a few weeks doing that two or three times a day, or thereabouts. I ended up getting another year's use out of them.

-------------
Maybe US Battery can provide some V/100A data for the US2200 batteries.

After we find out how much they drop vs how many Amps are being drawn, one of us should contact USB tech support.

Attached is a USB Tech service bulletin about chronically undercharged batteries. You need to verify the DPI is reaching at least 52.5V (2.5VPC x 21 cells) before the regular charge cycle ends and it goes into float charge. Since your DVM has a MIN function, it probably has a MAX function, so just connect it to the battery pack's main terminals and let it do the watching for you.

1. This is the link I followed initially http://www.dpipower.com/store/MNUL/General_Chargers.pdf
However, the back of my charger has a box with instructions and US Batteries are labeled as profile#1.

2. I probably have about 50-60 charge cycles

3. So basically keep a laptop connected and making a log while I re-do the voltage measurements?

4. Back in April when I realized the charge profile was incorrect based on what was on the charger I did about 6 back to back charges over two weeks.

5. I have checked the charged and it’s getting to at least 53.8v during charging

Lastly
What is the absolute lowest US2200 batteries should drop during load per cell before damage occurs?

Could anything else be a culprit outside of the batteries?

[Dwalls]

Not sure if this will help with what JohnnieB was asking about but here is the spec sheet on your batteries. US Batteries told me that the best way to tell the condition of your batteries is to check the specific gravity of each cell in each battery with a hydrometer. If you don't have one they are cheap and easy to use.

Hope this helps

[Conradconrad]

Originally Posted by Dwalls

Not sure if this will help with what JohnnieB was asking about but here is the spec sheet on your batteries. US Batteries told me that the best way to tell the condition of your batteries is to check the specific gravity of each cell in each battery with a hydrometer. If you don't have one they are cheap and easy to use.

Hope this helps

Thanks will buy one tomorrow. Any recommendations on what kind, probably from auto parts store

[JohnnieB]

Originally Posted by Conradconrad

1. This is the link I followed initially http://www.dpipower.com/store/MNUL/General_Chargers.pdf
However, the back of my charger has a box with instructions and US Batteries are labeled as profile#1.

2. I probably have about 50-60 charge cycles

3. So basically keep a laptop connected and making a log while I re-do the voltage measurements?

4. Back in April when I realized the charge profile was incorrect based on what was on the charger I did about 6 back to back charges over two weeks.

5. I have checked the charged and it’s getting to at least 53.8v during charging

6. Lastly
What is the absolute lowest US2200 batteries should drop during load per cell before damage occurs?

Could anything else be a culprit outside of the batteries?

1. That mode list in that manual is confusing. Glad you checked the list on the charger.

2. Ought to be pretty well broken in by now.

3. Yes. Please shift to Reverse for a second or two before accelerating up the steep side of the bridge for each battery. The max battery amps following the marker ought to be the amps being drawn when the voltage reading is the lowest. Also note the battery's voltage before starting up the hill, that will be the before voltage the low voltage under load drops from.

Also, in your original post, batteries 5 and 6 might be out of sequence. (V6 is higher than V5, while V1 thru V4 drop sequentially. With V5 and V6 swapped, the whole set of 7 drop sequentially.)

4. Do some more. Maybe one or two a week for the next two or three months. US Battery recommends doing an equalization charge every month.

5. USB says at least 2.5VPC up to 2.6VPC. That figures out to 52.5V up to 54.6V for a 42V pack, but the DPI uses dV/dT (change in Voltage over change in Time) for the finish stage cutoff, so it could get upwards of 59V as the batteries age. The important part is the charger is taking the pack up to the minimum and beyond.

6. 1.5VPC is the absolute minimum. That is 4.5V for a 6V battery or 31.5V for a 42V pack. That is the point where irreversible physical damage to the plates starts occurring.

During non-destructive load testing, the batteries are taken down to 1.75VPC, which is 5.25V for a 6V battery and 36.75V for a 42V pack.

------------
The tricky part of using the 36.75V and 31.5V numbers with the voltage readings seen in the data logs and a dash mounted DVM is that the voltage drop due to the resistance of several high current cables, connections and contacts is included with the voltage drop of the batteries, so there is some wiggle room when monitoring pack voltage.

The data collected in your tests will (hopefully) show how much voltage drop is in the cables connecting the batteries together to form a 42V pack.

[JohnnieB]

Originally Posted by Conradconrad

Thanks will buy one tomorrow. Any recommendations on what kind, probably from auto parts store

Get the weighted glass float type with a thermometer. Something akin to this: https://www.amazon.com/East-Penn-Tem.../dp/B0002KKTYU

OR a Refractometer akin to this: https://www.amazon.com/Refractometer...ZPMEJPYRZZQ8MW

Measuring the SG (specific gravity) of the electrolyte has art mixed with the science, so don't jump to conclusions until you've mastered the art and learned the science.