Battery recommendations?

[jgedde]

I just completed a JE Howell Farm Boy. It's been running off a 6V supply generated from 4 AA cells. After those batteries called it quits, I've been using a battery charger.

So, what's a good battery technology to use? I'd like it to be small and easy to hide. Also, easily rechargeable.

The engine has a "spark saver" so it only fires the plug when it needs to. That said, the average current draw is quite low. But, when the plug fires, it takes a big slug of current for a few milliseconds.

I was thinking of stopping by the hobby shop to see what they had to offer. Perhaps a LiPo or LiIon pack? I've never used one. Do they take kindly to big slugs of current? Is charging them an issue?

Thanks!
John

 

[petertha]

See my post #47. Hopefully it might get you started.

http://www.homemodelenginemachinist.com/f31/engine-transportation-display-box-21574/index5.html

The upside of Li* type packs is they are becoming dirt cheap in RC applications. The downside is you will need a charger & power supply for them. But those are coming down rapidly too & smaller wattage stuff is not too bad $$. Plus you will find a hundred uses for them like replacing crappy NimH cells in drills & tools you can no longer find replacements for

I'm actually not sure what the micro duration + 'big slug of current' would mean to Lipo/Lion battery substitution. But I suspect that anything that you were running succesfully off typical AA type cells, the Li* cells will surpass with flying colors. Thats what what the C-rating terms is all about. And you can simply recharge them vs. chucking them out like Duracells.

The trick is matching voltage. 6V... is that a nominal sticker value? Under load? Lion's are nominally closer voltage match. Lipo's are 3.7-4.0 volts per cell, so you are either under or over by a bit.

 

[Lawijt]

I work a lot with A123 cells. Powerfull & they can be mishandled.
LiPo is very good , but you need to be very carefull with those. I used them in my competition model racing boats. Under voltage kill those batts.
Then they swell up & sometimes burn into a heavy fire. And it is almost impossible to put that fire out.

Barry

 

[petertha]

Lawjit makes a good point for 123 cells (LiP04). You can buy individual cells or also pre-made RC type packs. The one advantage is they are closer nominal voltage to your 6v application (3.3v/cell). Thats kind of what I was getting at but worded clumsy.

http://www.hobbyking.com/hobbyking/store/__16576__a123_6_6vb_2300mah_2s1p_receiver_pack.html


Note that they are rated 6-10C. So in this case 10 * 2.3A = 23Amps capable. LifE are generally a lower rating than Lipo. Any battery chemistry has a risk of heat/failure under excessive current abuse, hence the purpose of C-rating. But a good safety point was given about Lipo fires.

You will still need to investigate safe charging for Li* cells in any event (this is another saftey issue!).

 

[OrangeAlpine]

Nothing to add, just a question. John, how much running time did you get from the AA's?

BTW, thanks for sharing the circuit. A major contribution to mankind!

Bill
​

 

[jgedde]

Thanks Bill,

As far as run time, it's hard to say. Maybe an hour or two before the engine became hard to start. The open circuit voltage is still OK but the spark became weak and the engine flooded very easily.

John

 

[Capt,n John]

I bought a power pac for a portable drill. It had 10 cells in it. Then I made a 3 cell pac and used a Model-electric coil. It seems to work pretty good.