lead acid charging

[dirty_d]

The bike im making will have 4 12v 12ah batteries, I dont have a 48v charger yet, will it be ok to use my 12v charger which has a 10A rate if i charge all 4 in parrallel for 2.5A each? The only thing im not sure of is that if some charge faster than others then one battery could get too much amperage.

 

[fechter]

Actually, charging all of them in parallel is probably better than using a 48v charger. Since the batteries are in parallel, the voltage on each battery will be equal. They will tend to share the current very evenly unless one battery shorts out or something.

It's going to be a hassle to rewire them for charging every time, and be careful not to mix up the connections.

A really good way to charge them would be to buy 4 separate 12v chargers. You can leave the batteries in series, and have wires coming out from each one to a plug (or plugs). This way the batteries will tend to stay balanced and you won't need to mess with the wiring to charge. To do it this way, you need to make sure the chargers are isolated, but that's easy to test and easy to fix if they are not.

I would not recommend a 48v charger unless you have some kind of battery balancing circuit. Over time, they tend to get out of balance, and the weaker cell gets fried.

 

[xyster]

Charging lead and lithium batteries in parallel is A-OK -- they act like a single, larger battery. Parallel-charging NiMH and Nicad is more complicated.

 

[Eric G]

Charging the 4x12v12ah sla in parallel with a 10amp charger should be fine.The spec sheet on my sla batts. recomend that charging amperage should not exceed 25% of the rated ah of the battery so in your case 12ah / 4 = 3amps.Anything more than 3amps you have to pay attention to heat issues.

 

[Beagle123]

You might consider a cheap 48v charger. I really like the convenience of just parking, and plugging it in without messing around with a charging configuration.

You can get a charger and a socket to put on the bike from tncscooters.com. The charger is about $40 and its 2.5 amp smartcharger that stops charging when battery is full. The plug is a few bucks.

I used an old computer extension cord for mine. It had a female three prong end.

 

[Instant Karma]

Come on guys at least go to Ni Cad packs, lead acid is for emergency outages and backup systems. I believe you can even use SLA chargers if you do some monitoring and some measurements. I even quit using lead acid for my electric lawnmower and now just use three 24V Ni cad packs at 24 lbs total instead of the 6 SLAs at 42 lbs in the cart behind the lawnmower.

 

[dirty_d]

i would switch but im just not willing to spend over $100 on batteries right now.

 

[Doctorbass]

What about puting 4 resistors in series to create some taps and help balancing during charging? cheap.. no need to use comparator for people that doesn't want to spend time and money, that way cost 4$

Using 4x 5W 100ohm resistor maybe like:

(-)----/\/\/\----(+ -)----/\/\/\---(+ -)----/\/\/\---(+ -)----/\/\/\-----(+)
0v``|`````|`14V`|``````|`28V``|`````|`42V``|`````|56V
|```\-SLA+/```````\-SLA+/``````\-SLA+/``````\-SLA+/```|
|`````````````````````````````````````````````````|
(-)------------------------------Charger---------------------------------(+)

simply remove forget all ````.. they are to keep the blank space in that "ascee drawing"...

The voltage would tend to balance right?
I know that would dissipate some heat and that the charging process would take more time, but that would help for sure.

Doc

 

[Eric G]

"i would switch but im just not willing to spend over $100 on batteries right now."

Exactly!!!

I've been using lead batteries for a long time and feel they've served their purpose well.With other chemistries there's more stuff to pay attention to,even the posibility of fire w/lithium.
If I were to change Id likely try NiCad because of the 1000+
cycles you could get out of them.Still the price of NiCad is prohibitively high for me.If I remember correctly I was quoted a price of somewhere's around 300+ Can.dollars for a 48v8ah pack of NiCad w/charger.

I have a 36v7ah sla pack and use a 36v 2amp charger and a 12v 1.5amp charger,at different times of course. I use the 36 volt charger for oportunity (quick charging) during the day for when I'm out and about.In the evening I haul the battery pack up the stairs hook em up in parallel for a long slow over night charge with the 12 volt charger at a C/14.4
rate,by the next morning they're raring to go. No problem with balancing as of yet although one batt. lags 1/100 of a volt compared to the other 2 which is insignifigant.

Different strokes for different folks I suppose...

Eric

 

[fechter]

I still use lead because I can get them for free and I'm cheap.
I sure do like those new LiFePO4 batteries though. I'm saving my pennies.

I'm hopeful that someday used Prius batteries will be cheap.

 

[safe]

This is sooooo easy...

I've got three SLA batteries that have three female Deans Connectors on the ends of their wires. So you have the "docking station" that can't electrocute you because it's female and nothing is exposed. Then you have three male Deans Connectors soldered together side by side in parallel which connect up to the charger which is an inexpensive car type that cost me $25. You then create a wiring harness for the bike where you have three more male Deans Connectors only this time you wire these three in series.

It costs next to nothing.

You only have three Deans Connectors to deal with.

It does not waste current. (Deans Connectors can carry 50+ amps)

Dean Connectors cannot be plugged in backwards.

It's hard to get electrocuted.

Deans Connectors seem to never wear out. (in my experience)

Sometimes the most simple approach is the best way to go... :wink:

(in your 48v case change all these from three to four connections)

 

[fechter]

What about puting 4 resistors in series to create some taps and help balancing during charging? cheap.. no need to use comparator for people that doesn't want to spend time and money, that way cost 4$
Doc

I think the current draw of the resistors would throw off the charger control circuitry. You would also need to remove them after charging.

A similar approach is to use big zener diodes across each cell to limit the charging voltage. This works quite well and you don't need to remove the zeners after charging.

 

[dirty_d]

i noticed on my 12v car battery charger that has a 10 amp rate, while charging my 4 SLAs in parallel only draws 6 amps when i first start charging is this normal? each battery is only drawing 1.5 amps which takes forever to charge them.

 

[fechter]

Probably.
I have a '6 amp' car battery charger that usually runs around 2 amps. It will do 6 amps for a while with a really dead battery.