Battery ballancing if there is no error code

I'm not knowledgeable enough to address the technical aspects but I do have an opinion related to your approach to the balancing issue.

I think for the convenience you might be better off spending a little extra now and going with a charger/discharger that won't require you to dismantle the battery every time you want to balance it. I'm in the process of getting the Prolong charger/discharge system (ordered this week, I'm awaiting delivery and plan to install the harness and balance in June). I'm not a huge DIY person and like that I can leave the harness in place. Then I can maintain the battery cells all at once without tearing the car apart every time.

 

I totally understand. Good luck with your task. I'm sure someone with a lot more knowledge than myself will help you out here.

 

...sorry I'm late arriving at your party, but here's my 2¢, read all you can about grid-charging, and the basic theory behind it. Hybrid Automotive's Prolong System is a good place to start. Jeff Sloane (Hybrid Automotive) is very helpful, and there's all manner of useful information to be had by using the search function here on PriusChat! Just remember that slow and controlled (both charging and discharging) is part of the secret! Good luck! (...and welcome to PriusChat!) - hope this helps

 

If you have done it before and are comfortable doing it again, I say go for it.
Yearly is probably good for an older battery pack.

I personally don't see much reason to go below 6v, but it's totally up to you if you want to go lower.

 

Would be very interested in other opinions on this topic and or comment.

When is it OK to discharge a pack below .8 or .5 volts?
When is it NOT OK to discharge a pack below .8 or .5 volts?

Some think that taking a healthy pack below certain voltages may not be in the HV packs best interest.

What is considered a healthy pack?

 

Even if you don't purchase a charger/discharger from Hybrid Automotive, I'd recommend reading the manuals for their devices. Their discharge procedure uses a stepped load, initially about 1.5 amp, going down to about 0.2 amp as the voltage goes down. The lowest voltage they reach with the fancy discharger is 17 volts for the full pack, which is 0.6 volts per module. I have to assume that the reason they go so low is that it is necessary for the best result. Note that they operate the cooling fan during the charge/discharge.

 

The HA system is really the best way IMHO but I have done both and was successful using the RC charger method as well. My suggestion is to use low current when charging and the highest settings possible when discharging. The idea here is to keep the modules as cool as possible (heat builds on the charging side) so if you keep the current low enough you are effectively grid charging but at the module level. Read the HA documentation as suggested above and it should be clear what the steps are that you are trying to replicate. Don't go below 6V per module unless you also use low current in the discharge process to prevent cell inversion. Hope this makes sense.

 

Keep in mind even the 2A is alot compared to what grid charging does........below are the specs on the Prius Prolong grid charger

Technical specifications (94-09 Prius):
Input Voltage: 88 ~ 264VAC
Input Frequency: 47 ~ 63Hz
Input Leakage: <2mA / 240VAC
Output Voltage: 0 - 250V
Output Current: 350mA CC
Max rated ambient temperature: 100 degrees Fahrenheit (38 degrees Celsius)

This is also over an entire battery pack so the reason why we need to use cutoffs on RC chargers is because the current at 1-2A is still high enough to generate enough heat to cause damage to the module once it reaches the fully charged state. It's hard to get to a fully charged state without the possibility of overcharging which is why the HA method tends to produce the best results. On the discharge side you want the highest current possible simply to save time when cycling, they can see huge amps in use but again the ECU never lets the battery out of the 40-80% SOC range.

Once you are done with the RC chargers (checking capacity) make sure to load test them all with a headlight as well.
Prolong® Battery Module Load Tester User Guide &ndash; Hybrid Automotive

 

Note also that the Prolong grid charger operates the cooling fan, even with 0.350 A charging.

 

Load testing looks pretty good, keep cycling them but use 1A charging to help protect the modules from heat damage.

 

That is the result of overcharging at too high an amperage (ie you reached full SOC) and continued to try and charge the module (thereby causing it to swell). It should be ok but this is why I suggested to use lower charge currents when doing this (at the expense of time of course).

 

I bought a few iMax B6 chargers (similar to your Turnigy) to do the same: preventative maintenance on my battery pack.

I started with bicycle NiCd (5Ah) and NiMH (10Ah) cells to get some feel for it and am glad I did.
I have an iMax 50W (charges at a maximum of 50W or 5A, whichever is the limiting factor) and two newer 80W ones (charges at 80W or 6A, whichever is the limiting factor).
The 50W version has no trouble sensing the delta V (on Auto, iirc it is set to 7mV/cell). The 80W versions never stop and always run into the capacity limit (even when set at twice the Ah rating of the cells, regardless if using Auto or 5mV/cell)
After doing research, I found information that a delta V can be hard to detect when the charging current is too low*. Advice was to use 0.5 to 1C to make sure it would be enough to sense the delta V.

Can someone confirm this charge-current vs delta V vs capacity relation?

I had hoped to use the 80W chargers as they can also discharge up to 10W, so I could simply cycle one Prius module per 80W charger and come back after 3 days with a nice list of discharge capacity and energy fed into the module for e.g. 4 charging cycles.

For now, the conclusion is that the 80W versions are worthless unless I can use them with a temperature sensor and skip the delta V meaasurement. So for now the project is shelved and I am following this thread with interest.




* the 50W versions charges the 10Ah cells with 2.5A and stops at rated capacity (+10% or so) as expected. The 80W version never stops, regardless if using 2.5 or 6A charging current on the same cells. I tried this on 10 cells (12V) and tried the 6A charging on 5 cells (as with 10 cells you would run into the 80W charging limit and not quite reach 6A).