Grid Charge HV Battery to Balance?

Make sure you cool things as you charge/discharge the pack, and keep things under compression.
Doing some preventive/maintenance charging would certainly keep things in check and is a good idea.
Glad to hear you are thinking ahead.

 

Thanks for the encouraging words. We hope so too!

Our fan motor control board is almost done. Functions perfectly on both 1st & 2nd gen HV battery fans. Just a few more tweaks and tests (and a green light from the patent attorney) and these will be ready for market .

 

Like Eric said, the voltage levels should work, but the 'car harness' would be completely custom. Also and very critical, you would need a way to cool the cells while balancing. For a one off, might be worth getting some sort of 120vac fan and fabricate a removable ducting setup.

We get calls all the time from lower volume hybrids such as this. We want to get car harnesses designed for all of them, but oh so little free time hahah

 

Would I still need to be concerned about forced cooling even in the middle of winter in eastern canada?

I will be experimenting with spare modules to get the hang of what I am doing before working on the full battery.

 

Totally understand serving the larger markets first. My biggest concern would be the charging system as I can definitely design a forced cooling setup (either using the stock system or retrofitting something onto the vehicle).

Thanks again for everyonés insight on this.

 

If you monitor the first module on a regular basis you will know how much heat is likely to be given off. Charging more than one module within thin pack at the same time may require some cooling. The lower the charging current the less the heating will be, but the charge times will be longer to compensate.

John (Britprius)

 

Makes perfect sense. I am looking to use 2 x 200 watt (self powered) Hitec X4 chargers so hopefully that would be the maximum heat dissipation assuming the modules were all at full capacity. I will just need to see how hot the setup gets on a steady state basis under those conditions.

 

For some of the people charging at high amp ratings for longer periods of time, I would suggest backing off a bit as you reach higher State of Charge. Don't want to make the cells overcharge and start venting!

 

When you say back off do you mean to lower the current down to 1-2A or to lower the mAh being delivered to the battery overall? Not sure my charger has that capability to alter current throughout the cycle if thats what was meant.

Testing a module today I did overcharge it and it started to vent as I could hear the cells bubbling at only 5A of current with 7500mAh being delivered overall. The cells started to bulge out slightly but it all seemed to go back to normal again when discharged. If this venting/cell deformation is bad, how do you prevent this from happening in the future.

 

Are you talking grid charging the whole pack or cycling individual modules?

Have you balanced Prius cells too? If so what values were you using?

 

My understanding is this thread was about charging the whole pack at a very low current to improve balance without having to take the pack apart.

MTL_hihy: It sounds like you really need to stop and do some more research on safely cycling your individual cells (different than what this thread was about). It doesn't sound undoable, but if you do it wrong you can easily destroy your battery. If you are seeing evidence of bulging/bubbling you are likely doing permanent damage to your cells. You may not have the correct profile loaded into your charger, as it should be slowing down the charge toward the top and I would think it should have stopped before that started to happen. You may also need to come up with a rig to keep the module compressed while cycling. I'm no expert, but I would proceed very cautiously and do a lot more reading until you know what you need to do to protect your cells.

Rob

 

I have done extensive research on the subject and discussed with many experts and it didnt seem like the settings I was using were at all going to be doing any damage to the modules. The bulging may be just a lack of clamping on my test modules (havent touched the ones in the car at all) which I will fix with a test jig. Yes the cycling of individual cells is a bit different from grid charging but you can apply the techniques to both situations.

 

The car is charging at a much higher rate, but it never is taking the cells to 100%!

 

Great discussion and certainly look forward to setting up a grid charger for highlanders too.

If you are looking for a beta tester I would certainly be interested.

 

Just a follow up on this......the test module above was damaged because:
1) I overcharged it (started cycle charging instead of D>C, capacity was also set a bit high)
2) I didn't clamp the module as well as I should have (best to attempt charging in the Toyota packs, not on the bench)

Had much better luck on the actual battery pack with lowering charge rates and capacity settings.

 

Yes lower current=better when grid charging cells above 100%. We are on our third & final rev of the fan motor control and almost done with the patent application. Will be doing final thermal testing next week and hopefully getting the patent application filed next week also. It's taken longer than I thought but we have a charger with fan control that is robust enough to be run in a hot Arizona summer, which was our goal from the beginning.

 

Charging rate (current) is the same whether it is one cell or the entire pack. They are in series, after all. The current flow is identical through all cells by definition, and voltage can vary. Were they in parallel, then the voltage would be consistent in all cells but the current could vary. 0.35 amps is WAY lower than 5 amps.

 

So what is the GenII top off charge voltage ? with 350mA current limited