Help: Using 1/2D NiMH @ 7-8Amp?

[ma_sha1]

Need some help from NiMH experts, please.

I recently made this light which was built on running 4x 4/5 Sub C 2000mAH. The batteries are rated 30A Max discharge rate.
http://www.candlepowerforums.com/vb/showthread.php?t=278919

Customer purchase the light & is using 4x 1/2 D NiMH & reported success & is very happy with the output of the light running on 1/2 D.

I would very much love to adopt these 1/2 D NiMH for SST-90 use,
as the capacity is nearly double the 4/5 NiMH.
http://www.batteryjunction.com/0-5-d-cell.html

The Questions is:

Can this 1/2 D NIMH handle 7-8A discharge?
Why is it only rated Max to 3.5A discharge while the 4/5 Suc C at half mAH capacity are rated for 30A Max?

Is the 1/2D NiMH Max Discharge rate grossly under rated?
Or perhaps, they simply didn't test for higher Amps & really don't know
the Max discharge potential?

I know 1/2D isn't popular around here, but it looks like a perfect solution
for SST-90 in a mag 2D platform.

Thanks very much for your help.

 

[SilverFox]

Hello Ma Sha1,

NiMh cells are rated for a nominal 1.2 volts. If you look at the discharge graph, that cell hold 1.2 volts at a 1C discharge rate.

Most NiMh cells will be OK with a 2C discharge, but they will heat up and you may suffer cycle life.

The only way to know for sure is to test some cells and see how they hold up. You can be sure that the voltage will drop lower than what it was during the 1C test. If you look at the voltage during the 0.5C test and compare it to the 1C test, you may be able to figure out the actual IR (or you can go with their figures of less than 14) and with that you can estimate what the voltage should be at a higher discharge rate.

Tom

 

[NeSSuS-GTE]

ma_sha1: Seeing your 4/5 SC build on the B/S/T inspired me to pursue the exact same 1/2D idea.

All 1/2D NiMH I found at established vendors were max discharge of 3.5A. Just like you found. EXCEPT for one type on Ebay that had the following specs:

Dimensions: 32.8mm diameter x 37.5mm long.
Weight: 95g
Nominal Voltage: 1.2V
Nominal Capacity: 4,000mAh measured at 0.2C (800mA)
Max Discharge Current: 12,000mA (12 Amps)
Max Charge Current: 4,000mA
Internal Resistance: <15m Ohms when fully charged

I hope that helps. But I still really liked your 4/5SC idea... so I'm torn right now.

 

[ma_sha1]

Do you have a ebay link?

I wonder if they are the Aero cells,

http://webcache.googleusercontent.c...p.htm+Aero+1/2D+nimh&cd=3&hl=en&ct=clnk&gl=us

They claim 3C to 15C discharge & ahve 4000mAH 1/2 D types.

Not sure who sells them in the US. But they are flat top,
I need button top or at least with Tab.

 

[ma_sha1]

Hello Ma Sha1,

Most NiMh cells will be OK with a 2C discharge, but they will heat up and you may suffer cycle life.

Thanks, that what I am thinking too, it's not like I am trying to do 5C.

I might just get some & Run it at 7-8A for 10min & see how hot it gets.
Because if they don't get very hot, then I think i should be OK.

They won't be blowing up like LI-ions, right?
I am not concerned about cycle life at all, just want to make sure it's safe.

 

[ma_sha1]

I found the cells on ebay & they have tabs.

So this is excellent! Thanks NeSSuS-GTE
I ordered some. I'll get 2x the capacity on my next SST build, Yeah!

 

[Rommul]

I just want to chime in that "1/2 D" cells are bigger than 1/2 the size of a D cell so four of them probably won't fit in a 2D mag.

 

[ma_sha1]

They do, the light I made had recessed Mag springs to fit the 4x 4/5 Sub C,
which is slightly longer than 2D batteries.

The customer appeared to have fit the 4x 1/2D in there without further modifications.

 

[NeSSuS-GTE]

Fantastic! I certainly look forward to hear of your results!

I suppose the biggest question to answer will be whether those particular 1/2Ds will drive the SST-90 too hard (as you warned in B/S/T). I am very curious to know what you find.

Are you aware of which kind of 1/2D cells your customer used in place of the 4/5 SCs? Maybe they have already learned an answer to that question... ?

 

[NeSSuS-GTE]

Here is another interesting high-current 1/2D option:

http://www.powerstream.com/RW.htm

98A discharge? :eek:
Too low of an internal resistance? Might just poof the SST-90?

 

[lemlux]

I have 10 of the Powerstream 1/2 D button top NiCads which have the same 2500 mAh / 98 Amp discharge rates as the NimHs. I'm told they were originally designed for battle robots.

I would think you want to use enough of these cells with a buck controller to run an SST-90.

What confuses me is that controllers I've seen (H6CC) max out at 6.7 Amp power handling capacity and seem to want 1.0V of headroom between the batteries and the emitter VF. I don't know if this headroom requirement is for the nominal voltage of the batteries or for whatever they've run down to.

In any event, it seems too soon to use these Powerstream 1/2 D's for a maxed out SST-90.

 

[ma_sha1]

Fantastic! I certainly look forward to hear of your results!

I suppose the biggest question to answer will be whether those particular 1/2Ds will drive the SST-90 too hard (as you warned in B/S/T). I am very curious to know what you find.

Are you aware of which kind of 1/2D cells your customer used in place of the 4/5 SCs? Maybe they have already learned an answer to that question... ?

Don't want to shock you, but my next plan is not SST-90, I'll drive a
SST-50 with 4x 1/2D. probably to 7-8A. Mate with 80mm Aspherical lens & try to beat DEFT FTP in throw:devil:. Don't worry, I'll fine tune the set-up to make the current exactly where I want it to be. The thing with DD is that
you can't just change battery types w/o measuring what's happening with the AMPs, it need to be balanced & adjusted.

The customer used some old 1/2D cells, no AMP spec. I think he is going back to 4x 4/5 sub C.

 

[NeSSuS-GTE]

It's no shock... it sounds like another impressive idea.
I may follow in your footsteps once again. :twothumbs

But I'm excited about this SST-90 for now. (My first one.)

Please keep us posted on your 8 Amp SST-50 progress. Surely many will find an interest in such a creation.

I'm particularly interested in your ideas for heat sinking on that.
What was max rated current for SST-50?

 

[fivemega]

Each 1/2D cell is about 36mm long and 4 of them will take space of 144mm which is about 24mm longer than 2D
If quad boring is not a problem, 4S/2P Eneloop AAs will work much better in 2D, easier to obtain, LSD, 4000mAh, Much more current capablity and much easier to recharge.

 

[NeSSuS-GTE]

I found the cells on ebay & they have tabs.

So this is excellent! Thanks NeSSuS-GTE
I ordered some. I'll get 2x the capacity on my next SST build, Yeah!

Any luck with these 1/2Ds, ma_sha?

 

[HarryN]

I am following along as I am interested in 1/2 D cells as well.

Harry

 

[ma_sha1]

Yes, I got the 1/2D cells & building a light with it here:

Enter the mag Dragon:
http://www.candlepowerforums.com/vb/showthread.php?p=3438766#post3438766


Follow the MagDragon thread instead, as I won't be making further updates here.