This is not a flight question but I figure I stand a better chance of getting battery experts in this forum than the other.

My Sullivan starter is powered by 12 Nicad cells (14.4v). They are wearing out. I made a new battery pack using Nimh cells (14.4v). This pack would hardly turn the starter over. I was told that due to the chemical ingredients Nimh batteries will not deliver power as fast as Nicads.

So my question is, if I make up a four cell Lithium battery pack (14.8v) will it deliver power fast enough to drive my starter.

If there are any inconsistencies in the above it is an indication of my battery knowledge.

Thanks in advance.

Ed S

[Carlyle]

Lipo's generally produce a much higher C rating then nicd's, and nicd's product a higher C rating then nimh.

The answer to your question... Yes, much more. but, you are going to want to make sure that you use the highest MAH cell's as possible. Try and use at least 2 or 3 thousand MAH cells.

I'm not 100% sure about the C rating of nicd cells, but I'm pretty sure they produce around 6 C... I might be wrong though, while lipo's generally product no less then 15... Some are as low as 9 or 10, or as high as 25 C continus...

Some quick math.

2000 mah nicd with 6 C output = 12 amps @ 14.4 volts.

2000 mah lipo with 15 C output = 30 amps @ 14.8 volts.

I might be wrong here... but I'm pretty sure I'm not.

If you are going to choose to do this, make sure you have a balancer for your lipo's.

Hope this helped.
Car

[moo]

Originally Posted by Ed Smith

I was told that due to the chemical ingredients Nimh batteries will not deliver power as fast as Nicads.

Insuficient current.

Physical as well as chemical properties, but essentially correct.

High current versions are available in all chemistries. I used to use Sanyo SCR NiCd batteries at 15C plus surge with no damage. (four minute run time on a 1/10th scale car)

NiMh have the highest self discharge rate.

[pmackenzie]

Originally Posted by Ed Smith

I was told that due to the chemical ingredients Nimh batteries will not deliver power as fast as Nicads.

I have to disagree.
That was true at one time, but not any more. The best NiMh are capable of much better output that the best NiCd packs.
Think about GP or IB cells, not the no-name ones.

Self discharge and lifetime, the advantage goes to NiCd.

Instead of Lipo cells, consider A123 cells for a starter.
No fire risk. Very long cycle life. Low self discharge like Lipo.
A 4 cell pack could use a regular Lead-acid charger.

Pat MacKenzie

[Squidbait]

Ed,

NiMH cells take a few cycles to break in before they can deliver full capacity.

Do 2 or 3 charge/discharge cycles and then try them again.

*edit* I just did a little research, and most new NiMH sub-C cells will do 25-30A... at least the name-brand ones. If these are new batteries, I think it's just a break-in issue.

[Flypaper]

I'd check out the A123 batts.too. Been using the B&D a123s with no problems dumping the amps.

[astrofler]

ED, how did you make up the NIMH pack? single cells? or two six cell packs?

any chance you might have a cold solder joint, or in the case of two six cell packs, wired them in parallel instead of series?

12 NIMH should kick your starter pretty good. are the cells new or used?

[jkaz]

sounds like an amperage issue for sure you don't mention the mah rating of the cells you used you will likely need some big cells to get enough amps to the starter check the rating on the original pack if possible and try to match it or better it

also you could check each cell for the correct voltage to confirm no dud cells then check the pack voltage and confirm that it is in fact at full voltage then check the voltage while turning the starter to see what the pack drops to with the starter engaged you shouldn't lose much voltage during this step then use a rag or a glove to load the starter by holding it be careful of course and see what the voltage drops to if it's less that 14v your pack can't put out what the starter needs for amperage

as for lipos they would work great but again your going to need a big lipo to get the amperage needed for the starter

does anybody know what a typical engine starter draws for amperage?

let us know how you make out

jonny k