Quote:
Originally Posted by duckwize
You said to make sure I have a balanced SoC,
|
The reason fall back to the 'usable capacity' thing... and the 'weakest link'.
For example:
If all 20 Sticks were identical resistance , capacity , etc.
But if Stick #1 were at 10% SoC ... the rest of the sticks are at 20% SoC ... the whole pack looses the bottom 10% ... because Stick #1 will bottom out first ... even if the other 19 have charge to give ... it wouldn't be usable to you.
The reverse also happens ... if Stick #1 were at 20% SoC while the other 19 were at 10% SoC ... than the whole pack looses the top 10% as Stick #1 would top out first before the others ... and even if the others still had room to charge ... it wouldn't be usable to you.
Attached is an example of the SoC variation that can creep into a pack over time ... The SoC variation (shown there) was effectively removing about ~2Ah of usable capacity from that pack.
Eventually if a pack get far enough out of balance you can get IMA error lights ... even if all the cells and sticks in the pack are otherwise still usable for resistance, capacity, self discharge , etc.
Quote:
Originally Posted by duckwize
I want to build a grid charger that Mike designed. I've just started to do research on it, have my parts list and I'm about to get the supplies, but the small hurdle is the civic fan control. Sounds like it's not as easy as the insight. If you or anyone has input on a grid charger and fan control, or useful links that would be great!
|
That kind of high voltage whole pack low amp trickle charger (I think) is the over all easiest / best method of balancing the NiMH pack ... it is also will be useful afterward 2 or 3 times a year as maintenance to correct any small imbalances that might develop.
The fan is needed to dissipate heat ... you can work with hacking the OEM fan (you are correct the Civic version is not as easy as the Gen1 Insight fan) ... you can install your own fan to move the air ... or you want do a low enough amp rate that the heat generated isn't as much of a concern (but it would take longer).
There are a variety out there ... Mike's is a great system (but AFAIK he isn't building new ones anymore) ... Peter in the UK also has a good simple cycler (but AFAIK not a pre-built product) ... EVpowers and Bubblebatteries both have offered balancing services in the past (I don't know if they sell the equipment)... etc... etc.
Quote:
Originally Posted by duckwize
I don't think I can even come close to charging all the sticks within .01v.
|
The +/- 0.01v is a level that you can be certain you will not have any issues.
Like other things ... you will have to decide how good is 'good enough' for you... some people are happy with +/- 0.1V.
The goal is to have all the cells and sticks you have tested and selected all be pretty close to the same SoC.
The difficulty of getting that SoC balance without using a whole pack low amp trickle charger is the self discharge rate of the cells ... See attached Graph I did from previous testing of the 40 sticks I have (other sticks might vary)... the time gap from when you finish the first stick to when you finish the 20th stick there is the potential for a SoC balance to be created ... due to the Self Discharge Rate... in a week or two it won't be a large difference ... but any difference is just effectively removing that % of your usable capacity.
Quote:
Originally Posted by duckwize
But like I said I haven't looked too deeply into my grid charger issue yet, but just looking for input.
Thanks again!!
|
You can always just 'do the best you can' at the stick level now ... and then later use the low amp trickle charger to correct any imbalance that might be there... in the mean time you're just down that % of usable capacity.