A123? and lead?

[REdiculous]

I've got another 18ah SLA on order that I'll parallel w/ the 20ah SLA I have but I'm wondering if I can add a small A123 pack so it's harder to hit the LVC on takeoff/hills. A serial pair of these would be 13.2v, correct?..
http://www.hobbypartz.com/a123-systems-4600mah-6-6v-2s2p.html

Could I add them in parallel when the SLA's voltage drops to 13.2v or is there a better way...or no way? Also what's the cheapest way to charge a pack like that?

Oh..and are there any better prices than that? later

 

[dogman dan]

You could paralell some 4s A 123's with each of the lead batteries and it would help. The A123's would have less capacity, but they would level back out when you stopped pulling on them. They might wear out fast though, if they are that much smaller.

I found it worked really good to paralell 8 ah nicad with 12 ah sla. It pretty much eliminated the normal sla sag. Your best option, though more expensive, would be to get a couple of the 12v lifepo4 batteries that come in a plastic case. (thundersky or sky energy?) But that is about $200 I think. For a bit more, you could get a 10 ah 24v ping to paralell with the sla's.

Paralelling lipo sounds interesting, but the voltages don't match so good. Sla 13-14v 3s lipo at 12.5 would get overcharged by the sla. 4s would try to overcharge the sla. I guess diodes would fix that if you want to paralell 4s lipo.

 

[REdiculous]

Maybe I can figure it out myself but there has to be a way that I can see the voltage drop a couple points and then automagically add the A123 in and take it back out when the voltage goes back up. I don't think I really need the extra capacity, just a little help w/ the peaks.

I liked the ones I linked to since it looks like I could make 2 packs and strap one to each side of my forks. The front of my bike needs some kind of ballast weight (steering is a lil sketchy) and eventually I wanna get a hub motor for the bike anyway.

I guess the thing to do is lots of research and saving...maybe by xmas I'll be clued in enough that I don't spend a fortune on junk. later

 

[dogman dan]

If it's a regular route, like a certain hill you climb to get somewhere, you could stop at the bottom, swap from lead to a small light lipo pack, do the hill with lipo, and then go back to lead at the top. Or have it wired in paralell, but have a switch that makes the final connection. you'd be connecting with the lead at various states of charge. Flip the switch and the lipo starts to pump about 200 amps down a skinny wire to charge the lead. Yahoo! So that won't work. But a switch that connects one battery or another would work. They just need to be big hefty switches though, for 30 amps of dc. Just using anderson plugs for a switch would work fine if you can stop for 30 seconds. The real solution of course, is to dump the lead and get lithium of some kind asap.

 

[REdiculous]

It's not a regular route or anything like that, it's the occasional high loads on a 12v inverter and 12v SLA(s). I'll switch to 24v at some point and a hub motor is on the list as well but all that is pretty far off still.

Some of my riding is pulling skaters to the store so I think a booster pack would really help. Even a small lithium pack should make a huge difference for the high-draw situations since it'd help me save my SLA(s) for cruising. In theory.

I've got another SLA coming and I can still tweak the gearing but I'm definitely starting to save for the dream system..lots of lithium...I'm just hoping I can eventually mix the two somehow until I can ditch the SLAs completely.

 

[dogman dan]

Yeah, you need a boost for sure I'd think.

But the thing is, you MUST have very similar voltages when you add a battery to another battery paralell.

If not, the higher volt one will start charging the lower volt one. With stuff like A123's or lipo, this might happen fast enough to cause some real fun. Such as boiling the lead battery till it explodes spewing acid all over everybody nearby. Or you could get lucky and the only result is a piece of wire instantaneously becoming molten in your hand. So that means charging both, and connecting them at the start, or at some point when both have the same resting voltage. So that makes having one battery 20 ah and the other 2 ah pretty awkward. If your lead battery is trying to recharge your a123's for most of the ride, the battery can handle that I think, but you better have some honking fat wires connecting them, because all that current flowing is going to get very very hot. Much better to paralell similar capacity batteries. But of course, if you had 20 ah of a123, you'd trash can the lead.

Again, diodes could help with this issue, preventing that kind of one battery trying to charge the other problem. And again, the real solution to your problem is going to take more than $100. Start small, and get some lipo I'd say. 5 ah of lipo and a cheaper charger to go with it will give you a few runs up the hill, and then switch back to the lead. later on you can expand the lipo pack size and voltage. The great thing about this Hobby King lipo is you can buy a few now, and pay for more later. They have so much power, a tiny pack can run a big motor. So next time you have a few bux, order the charger, and when you get more, order your batteries if you can't afford $100 to $200 today.