batteries in parallel

[mnplus1556]

hello. i was wondering: can this ping battery:
http://www.pingbattery.com/servlet/the-5/24V-15AH-V2.5-LiFePO4/Detail

be hooked up in parallel with this battery?: (there will be two of these in series to get 24v)
http://www.batterymart.com/p-12v-18ah-sealed-lead-acid-battery-1.html#tabship

if so great! is there anything i have to do to make it safe/possible? if not, why? is it because the different chemistries or because of different amp hours?

also a little side question: is it safe/ok to have 2 12v 12ah batteries in series to get 24v, in parallel with 2 12v 18ah batteries in series to get 24v? they are all sla and about the same age.

thanks!!

 

[auraslip]

Yes it will work.

The thing is - lifepo4 has a higher voltage. the 24v ping is more like 26v. So what happens is the ping discharges first, and THEN the SLAs will start to discharge. I did the same thing, and found that the slas didn't even start getting use until the ping was discharged pretty deep.

Of course if you pull lots of amps and make the pings voltage sag, then the SLAs would be providing power. I'd like to see that happen on a 24v system though.

is it safe/ok to have 2 12v 12ah batteries in series to get 24v, in parallel with 2 12v 18ah batteries in series to get 24v? they are all sla and about the same age.

No. It'd work just fine, but the smaller pack would discharge first. The voltage would drop low enough for the controller to hit LVC, and you'd keep discharging from the 12ah batteries until you fried them. You could buy a $5 multimeter at wal-mart and use it to watch he small 12ah pack. Then you could either disconnect it from the main pack when it started to run low, or just shut the bike down.


What are you trying to do? Get range on a budget?

 

[neptronix]

Another problem is that one battery type is more willing to give power than the other. You will end up depleting the SLA battery and it will probably go far below the voltage it's happy with.. meanwhile the ping is trying to charge it AND send power to the controller/motor.

This is a bad idea. i would not serial these batteries together. The voltage range difference of the lithium pack and the SLA pack is quite large, and you are going to bump up against problems. I am not sure exactly which, but try it out.. you'll find out the hard way, lol.

 

[dogman dan]

Yes, but as stated above, the slightly higher voltage of the Ping will try to overcharge the sla when you first hook up, or when the ping charges. The way to fix this problem is the use of diodes, to prevent each battery from trying to charge the other. Overdischarging the sla is less of a problem, as the one that discharges first goes dead, it's internal resistance increases, so only a trickle flows from the high resistance battery. It wold still discharge the sla further than 50% though, causing premature wear.

See tech section for diodes info.

Sla with sla will work fine without the diodes. paralell the two different sizes together, which creates a bigger battery, then do the series connection. Be sure both batteries are charged when you do the paralell connect. Connect a dead batt to a charged batt, and the dead batt explodes.

 

[mnplus1556]

ok thank you. i guess i won't try that then. thanks for the heads up. and ahah yah i don't want to spend like $600 on a battery. and i already have some sla batteries. so im a little confused on the sla's in parallel. i have:

2 12v 18ah batteries
4 12v 12ah batteries

how exactly do i wire them all together? i mean can i wire the bigger ones together in series then in parallel with the other 4 smaller ones in 2 sets of parallels?

like this:


18ah-18ah in series. 12ah-12ah in series. 12ah-12ah in series.

then do i wire these three groups together in parallel?
or is it like:

18ah-12ah in series. 18ah-12ah in series. then idk what to do cuz i only have 2 18ah batteries.

thanks everyone!

 

[theRealFury]

ok thank you. i guess i won't try that then. thanks for the heads up. and ahah yah i don't want to spend like $600 on a battery. and i already have some sla batteries. so im a little confused on the sla's in parallel. i have:

2 12v 18ah batteries
4 12v 12ah batteries

how exactly do i wire them all together? i mean can i wire the bigger ones together in series then in parallel with the other 4 smaller ones in 2 sets of parallels?

like this:


18ah-18ah in series. 12ah-12ah in series. 12ah-12ah in series.

then do i wire these three groups together in parallel?
or is it like:

18ah-12ah in series. 18ah-12ah in series. then idk what to do cuz i only have 2 18ah batteries.

thanks everyone!

The best way to put your SLA's together would be as below... assuming they are all fully charged to the same rough voltage.

18ah - 12 ah - 12ah (these are in paralell to make a 12v 42ah pack)

then do the same again to make another 12v 42ah pack... then series the 2 packs together so you have one 24v 42ah pack.

 

[dogman dan]

Yes, exactly that. In paralell, the different sizes don't matter. So paralell first to make packs of the same size, then you are series connecting the same ah in each paralell set.

 

[blueb0ttle2]

That is going to be one HEAVY bike though will all that lead .
Seriously, I find this topic helpful, since I was considering building a little 12AH booster pack for my Ezip. But I see that that will not be so practical, since I originally thought of wiring 24V 12AH to my 20Ah pack (Two 10AH packs in parallel). But, I see that I would have to rig it as 32AH of 12 V with 32 AH of 12V in series, and with the way the Ezip is wired that would be fugly 20AH Should be enough for me 'til I get me some lithium

 

[mnplus1556]

ahhh ok thanks. good thing i asked. ahaha and yah it'll be like 60lbs of battery ahah. but i'm mounting them low as i can to lower the center of gravity.

 

[mnplus1556]

anyone know about how many miles i should expect? it's a 24v 30amp controller. i will not be pedaling unless batteries die. it will top out at 23 mph and probably cruise at 22ish. i will set it up like this:


(parallel:18ah, 12ah, 12ah) in series with (parallel:18ah, 12ah, 12ah)

about how many watts need to be drawn to go 23 mph?
and how many amps per battery and per parallel circuit will be being drawn?

thanks everyone!!

 

[wineboyrider]

fugly

I love fugly and functional!

Dogman wrote: See tech section for diodes info.

Good advice. A diode is like a back flow shutoff valve for water it only lets water flow one way! The ping battery and all batteries with a bms need to be protected from power spikes and surges. It isolates the battery basically.
:wink:

 

[fechter]

Diodes will prevent reverse current, but at typical bike power levels, it might get pretty hot.
A Schottky diode will have less heating than a regular silicon rectifier diode, but they are more expensive and a bit harder to find. Either way, the diode may need to be mounted on a heat sink fot this kind of thing.

You can also use a large FET as a diode. Just tie the gate to source.

There is some basic series/parallel wiring information here: http://endless-sphere.com/forums/viewtopic.php?f=16&t=1312

 

[theRealFury]

anyone know about how many miles i should expect? it's a 24v 30amp controller. i will not be pedaling unless batteries die. it will top out at 23 mph and probably cruise at 22ish. i will set it up like this:


(parallel:18ah, 12ah, 12ah) in series with (parallel:18ah, 12ah, 12ah)

about how many watts need to be drawn to go 23 mph?
and how many amps per battery and per parallel circuit will be being drawn?

thanks everyone!!

Well the mileage you will get depends on SO many factors it’s impossible to say but you can do some basic calculations based on the controller and motor and on the battery pack. This is just my best guess and I’m probably not going to be on the money but here goes.

24v x42ah = 1008watts of power. Now this is only in theory because Lead acid batteries do not like being discharged at high currents like we use in ebikes so they just can’t put out that much. In reality you’re looking at getting 50% capacity out of them if you deep cycle them (not good for battery life) so say that you have maximum of 500watts of useable power in your battery pack.

If your motor is a 500w (not sure as you never mentioned your motor but just as a guide) continuous motor running on 24v then you are going to be drawing around 20.8 amps from the pack at 100% throttle.

your controller is a 30amp max controller so should be capable of putting out 20.8amps continuous to run motor at 500w. (Controllers usually only put out 75-80% of their rated amperage continuously)

So at 100% throttle you would be able to run for about 1 hour on flat ground. Now you have to find out what’s your max speed at 100% throttle (if thats 23mph then thats your rough answer). Once you know that then you know what your rough range will be.

Obviously this does not take into account terrain, temperature, wind speed or peddle assistance and all of these do have a marked effect on distance so hopefully now you will see that finding out how far your pack will take you is almost impossible to find out without getting on it and riding until it’s out of juice.

as for how many amps per battery and per circuit are drawn, i could well be wrong her but I’m under the impression that as you have 2 12v 42ah packs they will each split the load roughly 50/50 so at 20.8 amps each pack would be supplying around 10.4 amps. now as you have 3 batteries in that pack and one is 50% larger than the rest at 18ah that battery should supply 50% more current then the other 2 so your 12ah batteries should be supplying about 3amps each at the motors 500w rated wattage and the 18ah battery should supply about 4.5 amps. If you’re starting off from a dead start or going up a big hill then your controller is going to push as many amps as it can do into the motor so in these situations you can add probably 50% more to the amp draws on your batteries.

I hope this helps and as i say, this is only my understanding of how it works so if I’m wrong then someone, please put both me and mnplus1556 on the right track

 

[mnplus1556]

wow thank you very much for the thorough response. I am unable to read it now, I'm on my phone at school but I def will when I have time later thanks!