Same voltage, different amphours, in series?

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omegagamer89

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Title basically says it. I'm about to order new batteries and I'm wondering if it is ok to use batteries, in series, with the same voltage, but different amp hour ratings?

The specifics:
Its a 36v, 800w rear wheel hub motor. I have three 12v, 12ah sla batteries in series to power it. These batteries turned out to be starter batteries, so they're obviously not what i need. They'll take me a few blocks before dying.

I'm going to order some new batteries. What I was wondering is this; could I take, say, two new 12v 12ah batteries, and one new 12v 22ah battery. Hooking these up in series would result in 36v, like I want. But would mixing two different ah ratings like that cause any problems?

Any help greatly appreciated. ^_^
 
Your going to buy sla batteries?

You would have 12Ah in your chain, and when the 12Ah has gone, having a single 12v battery with 12Ah left is of little use.

It has been said that you only get half of a sla used before hitting lvc all the time. So your building a 6Ah pack. 6Ah@36v should weight 1500g and costs £55 in the UK + A bms and charger.
 
Yes, I'm using SLA batteries because Nimh and LiPo and such are far too expensive.

So what you're saying is, the answer is that I can DO this, but I wouldn't see any benefit out of the one battery being 22ah and the other two being 12ah? Basically, it would function as if they were all just 12ah? From what I've seen a 12v 12ah SLA battery costs about 20 to 30 USD on ebay, so theyre fairly affordable.
 
A 5ah 4s lipo battery cost $23.65 and weighs about 1lb. It has 74 usable wh. A 12v 12ah sla cost a little less but weighs 10lbs and takes up 6 times as much space and only has about the same usable wh's. Build a 5ah 12s pack for ~$75 and you'll get about the same distance as 3 12v 12ah SLA batteries if you run the same speed.

Please go to the User Control Panel, select Profile, and then enter your city, state/province, and country into the Location field (country minimum) and save it. This will help people help you. Example: Wylie, TX, USA. Without knowing what country you are in it's hard to make any recommendations. Thank you.
 
You need three new batteries matched as close as possible if you buy more lead. Look for EV rated types, such as those used in wheelchairs, or kids car toys, or scooters.

Once you get your new 12 ah lead, you might be able to still use the old ones. They won't suffer so much when connected parallel with the new ones. So each set would be one new and one old battery, connected parallel. Then connect the sets in series. Heavy bitch then though.

Lipo is great, but you need to learn a bit before trying lipo. It's not for everybody. Lifepo4 is what you should save up for.
 
Using different capacities in series is inherently risky for batteries because you risk running the lower capacity cells dangerously low (even into negative territory). Depending on the chemistry of the cells this can result in a hasty demise of the cells or worse. The practice cannot be responsibly recommended, IMO.
 
wesnewell said:
A 5ah 4s lipo battery cost $23.65 and weighs about 1lb. It has 74 usable wh. A 12v 12ah sla cost a little less but weighs 10lbs and takes up 6 times as much space and only has about the same usable wh's. Build a 5ah 12s pack for ~$75 and you'll get about the same distance as 3 12v 12ah SLA batteries if you run the same speed.

Please go to the User Control Panel, select Profile, and then enter your city, state/province, and country into the Location field (country minimum) and save it. This will help people help you. Example: Wylie, TX, USA. Without knowing what country you are in it's hard to make any recommendations. Thank you.
Click to expand...

Could you show me where you've found a lipo battery for that price? Everywhere I've looked they're $200 minimum... If I can get a lipo battery for that price, they I'll definitely go for it. I've just never seen one for that price. Also, I understand that if you use Lithium batteries, you have to have a battery management system. How much do those run?


So it seems the consensus is that its generally not a good idea to mix and match the batteries like I was thinking. Good to know. I'm just going to go with 3 batteries with the same rating.

Just for reference, this is the kit I have:
http://www.ebay.com/itm/Rear-Wheel-Electric-Bicycle-Conversion-Kit-24V-36V-48V-250W-500W-700W-800W-1000W-/290754592384?pt=LH_DefaultDomain_0&var=&hash=item43b252fe80#shId

I got the 36v, 800W version of it.
 
http://www.hobbyking.com/hobbyking/store/__18631__Turnigy_5000mAh_4S1P_14_8v_20C_hardcase_pack_USA_Warehouse_.html
They're out of stock now. When they get more in stock, wait on link until discount pops up for $23.65 each. Run these at 12s on your setup.
You need a balance charger to charge. No BMS, just a voltmeter to run.
 
Wow, that's pretty good.

Ok, now here comes the stupid questions... (I know basically nothing about Lipo, compared to SLA)

Would I need just one of those, or would I need 3, or...? It says 14.8v, but my motor is 36v. If I used 1 or 2, it wouldnt be enough, but if I used 3 of those, it would be too much. Wouldnt putting in too many volts like that be bad for the system?
What exactly do you mean by 'run these at 12s'?
Could you please provide a link to the type of charger I would need? Im not sure what to look for.
What do you mean when you said I need a voltmeter to run? I have a voltmeter, but I dont see how that could possibly be involved in the system actually running, since its a stand alone device. This is what I have, in case you're talking about something different: http://www.learningaboutelectronics.com/images/manualmultimeter.jpg

I apologize if these questions are obvious. I know nothing about lipo, as Ive only ever messed around with SLA.
 
omegagamer89 said:
Wow, that's pretty good.

Ok, now here comes the stupid questions... (I know basically nothing about Lipo, compared to SLA)

Would I need just one of those, or would I need 3, or...? It says 14.8v, but my motor is 36v. If I used 1 or 2, it wouldnt be enough, but if I used 3 of those, it would be too much. Wouldnt putting in too many volts like that be bad for the system?
What exactly do you mean by 'run these at 12s'?
Could you please provide a link to the type of charger I would need? Im not sure what to look for.
What do you mean when you said I need a voltmeter to run? I have a voltmeter, but I dont see how that could possibly be involved in the system actually running, since its a stand alone device. This is what I have, in case you're talking about something different: http://www.learningaboutelectronics.com/images/manualmultimeter.jpg

I apologize if these questions are obvious. I know nothing about lipo, as Ive only ever messed around with SLA.
Click to expand...

I cannot overstress this--make sure you fully understand how to put together and manage your pack before you buy and commit to a complex setup based on multiple lithium battery packs. Lithium is NOT like SLA. You can't be nearly as casual about the chargers you use, or how you use them. There is very real potential of fire with overcharged or otherwise mistreated Li cells. This is especially true of metal-oxide chemistries, but even LiFePO4 can flame out every now and then. Personally, I would not use a metal-oxide chemistry in a pack this large. BMS's need to be checked for proper operation on a regular basis. Please take this very seriously--it really can be a matter of life or death.

dh
 
There are two types of lipo pack. The one's assembled with an integral bms are the safest in use. Offering constant cell monitoring and protection all of the time. You have simply a power wire and a charger wire to contend with. This is what you should find on a commercial bike.
The other type of pack is generally a pile of batteries that users reconfigure to charge or discharge. Disaster threads almost always revolve around this kind of pack.

A bms is going to cost you about $70 But remember, A bms is for life, not just for christmas.
 
RC lipo packs do not have a BMS. you have to buy a BMS from bestechpower to monitor and protect the pack and to balance it when bulk charging. the risk is not just in overcharging but even if you use a balancing charger the output can short out and the heat generated by the short can provoke the lipo packs into thermal runaway. some people don't care about this because they don't believe in a BMS under any circumstance. so they never mention a BMS or the risk in any of their comments to induce people to use the RC lipo packs.
 
The whole anti-BMS thing is just crazy and irresponsible in my mind. It's fine to not like a crappy BMS that doesn't do it's job right, but to say nobody should ever use one is just nutty. EV's are not possible without them, period.
 
First, people have been using rc lipo on their ebikes for years without anyone dying that I know of. There are safer lithium batteries, but none with the energy density at anywhere close to the price. The main reason rc lipo is so much cheaper is simply because of the volume produced for the hobby market. It's all I use, and I've been using it going on 3 years with not so much as a puffed cell, much less smoke or fire. I consider it perfectly safe when handled properly. That means don't overcharge it or over discharge it. I use this voltmeter mounted on the bike to monitor voltage while riding.
http://www.ebay.com/itm/Waterproof-Digital-Voltmeter-DC-15V-To-120V-Red-Led-Voltage-Digital-Panel-Meter-/170846310527
Your controller is a 36V model. The motor doesn't care what voltage it gets. It would run on 24V or 100V with the proper controller. The normal 36V lipo equivalent of 36V sla is a 10s lipo pack with a nominal voltage of 37V. This would work on your controller too, but a 12s 44.4V pack will too and give you more wh per ah and a faster speed than 10s. I don't think you'll find many people that would recommend using a BMS with rc lipo. I certainly wouldn't. It's not needed and would only give you a false sense of security, Rc lipo is high power, A BMS would just limit that power.
A 10s pack is usually two 5s packs in series, for ease charging, and a 12s pack is usually two 6s packs in series for ease of charging as a single pack using a balance charger This is the charger I'd recommend.
http://www.hobbypartz.com/75p-1220-charger.html?gclid=CNa3z9_N57ICFayPPAod10MAPw
With a 12-15V 350W minimum power supply.
For a 10s pack I'd buy 2 of these.
http://www.hobbyking.com/hobbyking/store/uh_viewItem.asp?idProduct=15008
For a 12s pack I'd buy 2 of these.
http://www.hobbyking.com/hobbyking/store/uh_viewItem.asp?idProduct=16207
This will cost a little more than 3 of the 4s packs but will make charging a lot easier.
Here's a couple of places to learn about rc lipo.
http://www.rchelicopterfun.com/rc-lipo-batteries.html
http://scriptasylum.com/rc_speed/lipo.html
 
A BMS that limits the potential of your battery is the wrong BMS for the job, not a reason to not use one.

I use lots of packs without BMS's too. Effectively I'M the BMS, watching the battery virtually every moment it's in use. That doesn't mean it's a responsible thing to recommend to everyone else who may or may not be up to that kind of commitment to constant attention. These people are strangers to you and I, and most of them probably just want to use their batteries, not babysit them every moment they're in use. And in an OEM EV, not using a BMS is a non-starter. Such a design would never make it to, let alone through, development.

Lithium packs can be made to work without a BMS, but the user must be very diligent in getting their setup right and monitoring their packs throughout their entire lives. The wrong BMS can be just as bad or even worse than none at all, but blanket vilification of use of a BMS is just wrong. The right solution for most (non-technical) users is a proper BMS combined with a realistic maintenance/checkup schedule.
 
So assuming I went with the 12s pack that wesnewell linked to, what kind of bms would be a good fit? How much do they cost?

I'm still torn between staying with sla vs going with lipo. I like that lipo is so much lighter and gives better performance, since I'm really not fond of 40ish pounds for my battery pack with sla.

However, I'm hesitant to go with lipo because its a whole lot more complicated and i don't like the hassle of it. I want to just plug the battery in, ride, then when i get to my destination, plug it in to charge on its own as i go about my business. Im kind of turned off of lipo by all this need for special chargers and bms and volt meters and all thistr extra stuff in addition to what i already spent on the motor, and what I'm going to spend on the batteries. But then again, i really don't like how heavy the sla batteries are... Lipo just seems like its all needlessly complicated though.

An additionalquestion; what's a good price for sla batteries? The best I've found so far is a 12v 35ah for about $70 on Ebay.
 
He linked to a 4s pack. That is 4 cells in series, in a box. Exactly the ones I am using, and you need 3 of them to make a 12s battery. You want to pop these 3 little boxs in a bigger box with a bms. From then on, you only connect to the bms. Both to tap off power, and to charge. In this case to charge with 50.4v. A 240w charger will do the job in about 90 mins. Cost around $60 delivered. If you can wait 5 hours to charge, then a $25 charger would do.

I have forgot where you are from, but how about one of these http://www.bestekpower.com/444v12spcmbmspcbforli-ionli-polymerbatterypack/
 
Best if yousave your money and buy a working plug and play prebuild pack. Like a lifepo4 with bms plug and play. There is not magic cheap way out. A Ping battery is great for you to begin with. Remember plug and play. A cheap battery is most likely a junk battery. Don't go lipo at this point but after 1yr. of reading and understanding then make that choice. Lot's of danger...
 
999zip999 said:
Best if yousave your money and buy a working plug and play prebuild pack. Like a lifepo4 with bms plug and play. There is not magic cheap way out. A Ping battery is great for you to begin with. Remember plug and play. A cheap battery is most likely a junk battery. Don't go lipo at this point but after 1yr. of reading and understanding then make that choice. Lot's of danger...
Click to expand...

Do you have a good pre built lipo pack you world recommend? Something that's a total kit, just plug it on and ride.
 
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