so i have the carbon pile 100 amp load tester and i have a few questions because i bought a box of untested subpacks from Bumblebee batteries. so far what i have done is charge all the packs to full @ 1c for every one of the subpacks(12 cells). Let all of them rest for at least a day or more. Never discharged, just charged to full from box and history unknown of how long these packs were left sitting.

1. most subpacks were off, BEFORE charging, by about .05 to .19 volts.
2. the 6 subpacks out of the 11 subpacks that i've LOAD tested NEVER went below 5.4 volts per stick even after going past 40 seconds. Lowest i've seen is 5.8volts per stick. Also the first subpacks i load tested were the subpacks that had the least difference in stick voltage per subpack, i.e.; subpack 11.59 each stick @ 5.78 and 5.81
3. i have tested the stick voltages by taping one end of the volt meter to the welded end and just went back and forth while doing the load test.
4. also the packs i've tested after leaving for 10 mins roughly after the load test bounced back to about 7.78 and 7.78 from the 7.84 and 7.86(this is just one example i remember)(volts at rest after charge and before load test) respectively ( last one i tested, that i remember)
5. also another big thing to note is i've only tested 6 out of the 11. the 5 left are still unknown.


so with the background out of the way. was i lucky that all the sticks i've load tested so far are good?

what else should i look for in building a decent pack( i know i may not get a great pack but a decent one that may last a few months without a grid charge), what else do i have to look for after these load tests and building my battery pack?

also i when doing the pack rebuild, i will be cooling the main pack with 3 computer fans at full by running a new dedicated line to the fuse panel.

any tips would be greatly appreciated.

thanks

 

Carbon pile or simple heating element? The carbon pile ones are usually 500A.


1C to what termination criteria? What equipment?


1C = 5.5A?


1) what were the subpack voltages, or are you talking voltage differences between sticks within a subpack.
2) that's good. What was the starting voltage of each?
3) that works, but your VM may have a slightly different error when measuring (-) voltage.
4) They should always bounce. Ones that behave differently are either the good ones or are the bad ones.
5) okay


Background is incomplete. Actual values should be included. Maybe share a google sheet with everything documented. Moar data.


When building any pack capacity, internal resistance and self-discharge are the key factors.


3 computer fans - meh. If you insist, get the loudest, highest cfm 120mm fans you can find. These will be farts in a hurricane compared to what the IMA fan can do.


Good luck,


Steve

 

sorry the centech 100amp with the heating element. 1C at 5.5 amp per hour. it's a hobby computer controlled custom built charger that i built for my rc's a while back(8 years ago?) with a seperate 1500watt dc power supply and is capable to discharge to another pack. termination was cut at 120f( but again i only have 2 probes so it's not really reliable and peak voltage cutoff at 18v.

1. i took voltage by subpack and also by stick and wrote them on all the sticks.
2. i will post the full voltages once i complete the 11 but the one i remember off the top of my head was 7.93 for both sticks and 7.80(voltage after a 10 min cool down), after a 40 second 100amp load test on a pair. that was done today at my office. but the other 5 were not far off from those numbers. i just don't remember exactly which pair did which numbers. so it lead me to believe no one cell is really holding it back.

Pack Resistance seems ok meaning linear throughout the pack but im sure the temp doesn't really mean much in ir. no one cell gets hot when getting charged and around 17.8-9 volts the cells are reaching about 105F- 110f, that's what im getting at.

Also just for insurance, once i get the best pairs together with similar capacity and voltage values, i will put it together after they are all charged full and then do a full discharge to <1v and then do a quick charge to 130v and shove it in the car and then do some 12v resets and the top it off with a 8-10 hour grid charge.

The computer fans got me thinking, i mean from looking at the battery compartment, it looks like honda designed the compartment to pull air from the cabin, into the battery and then suck it back into the quarter panel? but the fan being on the other side of the battery, i thought there may be parasitic? loss when the air get's pulled. i mean if the aluminum panel isn't air tight some sucking power can be lost when it's NOT going full blast, which i NEVER did hear ever. so what i thought was if i put computer fans(31cfm) to the case to help move air to the inside of the pack a bit maybe it will help with the pack getting so hot quickly and ruin the batteries quicker. If anything i would think HEAT is the biggest factor of damage to the cells more than anything. it can't hurt. lol

Thanks for the reply Steve.

 

Okay. You're getting very nearly 60A at the single stick voltages. With the 100A tester.


Nice unit. Pics? Plans? Temp is a good criteria provided the cells are reasonably uniform (within say 10°F). I'd stick with 110°F if possible. Watch out for outlier hot cells. Cheap IR temp probe is helpful. A timed charge to 1.3 X capacity is a good guideline, 7150mAh input or 1 hour, 18 minutes @ 5.5A.


How much current can it discharge into another pack?


1) good.
2) things are sounding pretty consistent. You may have gotten lucky with a good box of sticks.


Please do not do the <1V pack discharge. Since you have testing capabilities on the individual sticks, and plan to do capacity tests, there is likely nothing to be gained from pack cycling at this point unless you believe there is voltage depression still in the individual sticks.


Once you've done your initial load and capacity testing, you need to assess SD:


Start with discharged subpacks
Charge each for 42 minutes @ 5.5A (70% SoC target).
Let them sit for 7 days.
Record resting voltage prior to test.
Apply 60A load test for 15 seconds.
Record voltage immediately PRIOR to load termination.
Record resting voltage after 30 minutes
Record capacity remaining to 6V per stick


The outliers are either the good ones or the bad ones... If most of your loaded voltages and capacities are high and a few are lower, then those few are bad. On the flip side, if a few of your voltages and capacities are high but most are low, most are bad.


You have the cooling system concept down. Even if there is leakage/loss, demand is based on the pack temp sensors, so if it's not getting enough air to cool it, it turns the pack fan on higher. More importantly than anything else is keeping the interior cool to feed the battery cool air.


The fan can pull about 100W when running full blast on 12V. We're talking leaf blower type air movement.


120mm fans won't hurt.. just make sure they move a lot of air, or it's a waste. You have it right on heat being the biggest damage factor. Without a doubt.


Rolling down the windows to purge the hot interior air can help address your concerns.

 

Ok i will post all results that you have mentioned in the following days to come.

Also i do have a handheld ir thermometer, the program is set to trigger an alarm around the 17.7 volt range and i check all 12 cells in the pair and paste the temp probes on the hottest cells in each stick to monitor the temp to reach max delta which will trigger cutoff if max 120 degrees is reached. Ill change that to 110 next round

But to be off the topic a little bit i came to my conclusion that the fan isnt sufficient because if anything from other posts ive read it seems that batteries in the middle of the pack where All the heat resides and cant escape, which then builds up, seems to be the most problematic area of failure most of the time. That half proves that either the temp probes or he fan isnt sufficient enough to help the battery maintain a steady temperture, either the probes arent reacting fast enough or the fan im sure is strong but isnt providing enough airflow to the battery, or the probes on the pack senses temp drop and cuts airflow when it should maintain steady air for cool down. Whatever the case is i dont know how the system works or reacts so i cant say for sure but i believe a steady airflow along side the oem system surely can help sustain a better temperature when that airflow is directly attached to the pack itself and always on. To be simply put most people dont realize even with a small 30 second pull from the load tester actually showed rise in temperature and if you multiply that by 11 in a small enclosed case heat can build extremely quickly even in a cold start or even going all electric which can easily draw at least 30 amps i assume to move a 2800 pound object. Another reason being is when i rebuilt my hch pack, chargin with a fan at the start and having a fan trigger at a certain temp, final temp and voltage on the same stick were different many times that leads me to believe that having fan at least moving air past the center subpacks can greatly increase efficiency and health of the packs and also prolong the life of these packs. But again this is just speculation and assumption. Tomorrow ill be doing my base load test on a few other pairs and then i will charge all the packs by this weekend to 70 % soc and see what results i get. I mean for now im hopeful as at least half the box of pairs i received are somehwat healthy. I will have to disharge all to a voltage to set a baseline and then charge them back up.

Thanks for all the help, also i forgot to mention the pack to pack transfer i only tried at 6c on a 5500 mah lipo pack which drained it pretty quick to the discharged pack ina few minutes while it topped off the pack to 100% and the delta cutoff on the discharging pack was set at 20% to not destroy the cells. Never tried above 6c as the 10c and 30c and 50c rates would burn through my wires quite quickly lol, never bothered with it because i always needed charged packs

also please excuse my typos and this was typed on my phone

 

First, OMG... I would punch a baby after typing that on a phone.

At 110°F, you're close enough to full to not matter, > 95% SoC.

6C is overkill. 3-4C is a very good indicator of usable capacity. I personally use 20A.

The primary issue with the overheating is the **** decision to use "D" cells. They are fat and circular. it's a long way from the center of the cell to a cooling surface and flow around a cylinder is terrible.

Even when you can't hear it, the fan is moving a respectable amount of air. Here in Phoenix, I would frequently hear the fan shutting down after I powered off the car.. you really had to listen for it. The fan is almost never off. It's PWM controlled and can run at very low speeds, and it's almost always moving air.

Funny, I've always found the center subpack with the thermistor on it to typically be the better of the subpacks.

Keeping the interior cool with A/C with the center vents directed over your shoulder towards the rear deck will help.

Since you're an experimental guy, you might consider mounting a temp probe in the exit duct... maybe a MAF of some kind?

Again, you're not going to hurt anything... just get some loud little beasts.

 

lol @ first line.

I totally agree with you on the decision to use D cells. i mean if there was a way to wire up the prius cells and then just use the civic's controller would be awesome, while being able to maintain the stock battery location would be perfect but, it's not a perfect world.

Really? wow, hum... then im probably wrong about the cells in the center being bad.

Yes, i got the window visor/wind deflector crap to leave my windows cracked open in the summer so at least it can vent some of the super hot air out even if left in the humid NYC heat.

and funny you say that, i am an IT Director for a construction firm and i have access to 4 AMP beasts that push about 250 CFM each but then i mean i won't be able to live with the constant whine so i decided on my 31 cfm fans LOL.

im going to start doing the discharging today to 1.2v/cell and then charge them up to 70% soc using the 42min@1C method.

also here are the results for 3 out of the 5 i haven't load tested yet. i wanted to finish off the load test on all cells before starting discharge to 1.2v/cell then charge to 70%soc then load test, test. LOL


so here goes

pair "J" unboxed voltage 13.24 - 7.03/6.21 after full charge voltage 16.23 - 8.08/8.15 settle for 2 days voltage 15.77 7.88/7.90 30 Second Mark at 100a load test @ 6.08/6.11
pair "F" unboxed voltage 11.64 - 5.93/5.71 after full charge voltage 16.42 - 8.25/8.17 settle for 2 days voltage 15.51 7.79/7.72 30 second mark at 100a load test @ 6.07/6.03
par "I" unboxed voltage 11.69 - 5.75/5.94 after full charge voltage 16.36 - 8.11/8.25 settle for 2 days voltage 15.66 7.76/7.90 30 second mark at 100a load test @ 5.98/6.11

all cell voltages are in their respective order.

that's all the data i have for now. im going to move my cells to my office tomorrow to do the discharge and charge to 70% to load test, test. i'll get you better results in the coming days.

also the data i have for the pairs up top were the most mismatched set of the box. the other pairs had better results if i recall correctly.

but it seems all passed the load test. and the load tests were done probably to about 45 -50 marks on these cells. but still never dropped below 5.8.

now matching these pairs and placing them strategically will be a pain.

 

That's just my observation on the 15 or so packs. Given that one has a temp sensor on it, it should trigger increased cooling with temperature rise. It may be that it's towards the top of the pack and the subpacks behind it don't get enough cooling.


Looking good so far.


Not sure why you want to discharge to 1.2V/cell. You won't get much out of them. You need to discharge individual sticks to 6.0V or a 12 cell subpack to 13.2V.

 

ok i'll do the 1v/cell on stick level discharge. im reverting back to my rc days. we usually had a alarm/cut at 1.2 volts and always recharged to at least 1.45 per cell.

 

For batteries fresh off the charger for RC use, they will deliver most of their capacity above 7.2V, thus if you want to maximize battery life by limiting discharge, 1.2V is a sensible cut-off. On ones that have been resting for any significant period of time, more capacity will be delivered below than above 7.2V.


1.45V is also likely to fall short of 100% SoC unless it's at low current (0.1C). It really sounds like your 1.2-1.45V approximates 30-80% SoC range for use. I can see how that would make the batteries last longer.


You need to know the performance of the sticks through the entire range for comparison purposes. The car uses them between 20 and 80% SoC. Their overall health throughout the range dictates their performance in the operating range.