100+ NiMH AA (2000mAh) cells; integrate with lead-acid and LiPO4 system?

[DamonHD]

When the current round of OpenTRV experiment/tests finishes in Spring I shall have something like 100+ new NiMH AA cells coming back to me, which at 200Wh+ is a couple of days' consumption of my server, so *may* be worth integrating with my existing battery system which is ~2kWh of gel lead-acid and ~200Wh of LiPO4.

I'm not quite sure how clever or not to be with a BMS, and I also know that the self discharge is high (empty in 3 months) so I was considering simply using the NiMH as a sort of dump load for the LiPO4 when it is full (>14V).

Or I could potentially push some storage upstream of the lead-acid MPPT and LiPO4 BMS to spread peak flows (and losses).

Or maybe I should leave well alone!

Rgds

Damon

[Bruce S]

IF those were mine  I would use them in front of the LiP04 set.
Since you know NIMh are work horses and like NiCds can take a discharge swing down into 80% DoD; they would be a fair heavy use bank.
Their charge cycle is very well known and could easily work right along side either other banks.
However IF you wish to integrate without too much work use 11 of them per stick as NTL use to call them and the full charge will be able to withstand the same charge range as a SLA, otherwise 12 per stick will be even better.
I don't see where you come up with 200Wh tho, I get 20Ah at best 16 with 12/stick
Cheers
Bruce S
 

[DamonHD]

1 cell is 2000mAh at 1.2V or thus > 2Ah@1V = 2Wh.

Thanks for the suggestions Bruce.  Really just paralleling them up in strings of 11 or 12 with my gel lead acid behind my fancy Morningstar MPPT controller will just work?  Certainly an interesting thought.  I could put a bunch of them near the load (the server) in that case.

Rgds

Damon

[Bruce S]

DamonHD;
In ALL the testing I did, I found the 12/stick worked best without worry of temp or voltage issues.
My DSL and main server is on the NiCd 20Ah bank 10 cells/stick ; (the heavy use bank that is first).
The 16Ahr bank 12 cells/stick is connected along side the SLA 65Ahr battery.
I must confess tho  this is not an original idea of mine, I borrowed the thought from a guy who did a bunch of testing on his Corbin Sparrow e-vehicle to get further on it.
Hope this helps

[DamonHD]

Well, I can easily try the first stick of 12 sometime very soon.

If nothing else I can use try it as a way of charging 12xAA at once!

Rgds

Damon

[Bruce S]

Unfortunately I haven't seen NTL post for quite some time, he did a lot of testing with the PVC light sticks he built.
IF these are true sized AAs then You could do that, but maybe like Norm has done, there's a better way. Do them in more manageable sizes, like 6 in a string side by side? In a PVC tube our USA based thin walled 1/4" ones (I think will be loose enough and tight enough to hold them securely.
I'll need to do some digging in Norm's old posts and see if the pictures are still there along with the instructions.
Being that these are individual AAs you have a lot of flexibility.
Have fun too.
 
 

[DamonHD]

The "having fun" part is the main thing on my agenda!

Rgds

Damon