Battery question - SLA

[oldpiper]

Yeah, I know some of you have already got the answer: "Dump (recycle) that cr*p and get some REAL batteries." But, please read on. Here's my situation, I commute a short distance to work, over city streets, my 36V 12Ah SLA setup gets me there and back, no problem with range, or AFAIC, with speed, generally. My only gripe is that I wish I could get off of one particular light faster (OK, all of the lights faster) from a standing start.

I realize that my problem is with the sag of the battery when pulling as much current as I do out of it. So, short of spending 3/4 of a kilobuck or more, I figure I could go blueb0ttle2's route and parallel some extra SLA's in there to get me more amps when I need them. Looking on the net, I find that I can get another 7Ah of RC batts for about $50 or motobike batts with 50 CCA for about $60. Is the 50 CCA a faster discharge? I have no idea how to compare the two. My thought is that maybe once I get moving, if the moto. batt discharges/gets me moving faster, it would be at least partially recharged by the SLA's I have in parallel. Does this seem reasonable? Would the RC batts do me just as well? Should I just plan my route so that every intersection I might have to stop at would be going downhill? Would an ex-Marine drill sergeant make a lousy psychotherapist? (love that particular insurance commercial)

Thanks,

Cameron

 

[neptronix]

Depends on what you're referring to by RC batteries. If you're talking about lipo RC batteries, forget it. It will be a hassle to recharge two batteries at once. You'd have to seperate the lipo from the sla and hook them into different chargers each time.

Paralleling some SLA would help but consider the weight.

So you need to either go big or go home. Adding more SLA to run in parallel will help, but do you really want to invest in SLA when you can get 10ah of lipo for about $200 shipped that would give you virtually no problems with voltage sag... less than half the weight.. and longer life?

 

[oldpiper]

Depends on what you're referring to by RC batteries. If you're talking about lipo RC batteries, forget it. It will be a hassle to recharge two batteries at once. You'd have to seperate the lipo from the sla and hook them into different chargers each time.

Sorry, I wasn't clear. They're SLA, so I'd just charge them in parallel with the existing ones, not having to unhook anything.

Due to other circumstances at the moment, my first priority is to go with as little time and hassle spent on maintenance as possible, and I'd like to get a year or so out of the batts I have (from last Oct) before I scuttle them (that's the Scot in me coming out :wink: ), so if $50 or $60 can get me by until then, that's what I'd prefer. I'm predicting that by early next Fall my situation will have loosened to where I can start to really play with this stuff.

Plus, I'd like to be able to upgrade my bike and my boys eZip 500's (2) at the same time or even get them into an ebike, and I know that won't happen until the summer, anyway. (It's an "in order to ensure domestic tranquility" thing)

Cameron

 

[Jeremy Harris]

If you have the room and don't mind the extra weight, then increasing the capacity of your existing lead acid pack by adding extra batteries will reduce the sag a bit and maybe give you a little bit more oomph, but I wouldn't expect to see a really big improvement in performance. To some extent your controller will already be compensating for the battery voltage sag anyway, as at low speeds the full battery voltage won't be fed to the motor, the controller will be cutting it back, almost certainly on the current limit as you accelerate away from a standstill.

Generally speaking more amps = more torque (which is what you're after) and more volts = more speed (not an issue when accelerating from a standstill). You might want to try increasing the controller current limit a bit, as that might do the job, at the expense of hammering your batteries a bit more.

Jeremy

 

[blueb0ttle2]

I agree entirely, if it is acceleration you are after, hooking up more batts in parallel is the way to go. I am running 20AH at 24 volts, which doesn't weigh all that much, but 36 volts at 20AH or so might be a bit much depending on the frame. That being said, if your bike has room, and is strong I don't see why not.
I myself am planning on upgrading another 24 volt bike to run on 36V, so I can go a decent 17-20 instead of a measly 13 mph.
I try to plan my systems to get torque rather than speed, I can't afford both

 

[RallySTX]

Cameron, CCA stands for the reserve capacity of the battery at 32 degrees, or below. No relation to C rateing. The C rateing used on LIPO batteries denotes multiples of discharge rateing. As in a 10C battery can discharge at up to ten times the listed rate. SLA batteries as I know them are only standard rate batteries. Headway cells can be had that give 10c, LIPO packs can go as high as 45C. At least that's what I have found. Looks like the cheapest route for now would be another set of SLA. Good Luck.
Brian L.

 

[Lessss]

Toss the lead. Pick up some headway 8 ah batts as their price is falling cause everyone wants the 12 or 16 AH ones. You could load yourself up with three 48V packs for 24AH for the same weight(not volume) as your current SLA.