Connecting batteries in parallel

[Gloop]

I want to connect three 60V10Ah batteries in parallel. Can I just use two of these wires?
http://www.ebikes.ca/shop/ebike-parts/wiring-accessories/dualbattcable.html
I'm going to be doing a tour and want the 3x60V as my main battery, with a 48V10Ah as a reserve.
Or do I need to use diodes?

 

[ddk]

To paraphrase the song "Mrs Robinson"
"We'd like to know a little more about you(r) (batteries) for our files"
until then the simple answer is: probably

 

[dnmun]

if you need to pair them up at the P- and B+ terminals it would be better to actually solder the connections imo.

if the BMS has a separate charging lead then you have to disconnect the two batteries from each other at the P- spot while charging to allow the BMS to protect from overcharging.

if you intend to carry a third battery then consider building it up to the same 20S length to match the others and run it in parallel at the same time to keep the C rate down on each and it will allow you to use the batteries in the top of their SOC range for the longest so they will survive better.

or you can tie each channel together through their sense wires for all 3 packs and it will function as one pack, even during charging.

 

[dogman dan]

If you can post us some clear pictures of your bms's, then Dnmun could perhaps draw in how you'd connect the bms's so they are properly paralleled.

I think you could use a quality connector like a 4mm gold bullet on 12g wire to do the adapter. the other end soldered to the bms.

Wouldn't it be great if typical bike batteries came with a plug marked, "for parallel connecting". Alas, few need it, so it won't happen.

 

[dnmun]

with the BMSs that have the same lead for charging and P- then they can be charged up in parallel without disconnecting but if they have a separate C- lead then you have to keep them isolated during charging. except then there is always the risk that one is not charged to the same level as the other so when they are connected in parallel the rush of current from the higher to the lower battery will cause over current shutoff so then both of the packs are isolated from each other through the drains at P-.

it would end up using only the lower voltage pack since it would be the higher voltage pack that shuts off so you can reset the BMS on the higher voltage pack by charging the lower voltage pack up to the same voltage as the higher pack.

so it depends on the BMS used in the pack in terms of simplification.

best is to parallel both packs at the sense wire level. you can continue using both BMSs in that case and if you pushed the 16S pack up to 20S then you could tie all 3 together through the sense wires and split 2 B- leads from the expanded pack to each of the two previous pack BMSs and connect the split leads at the B- spot on each of the BMSs.

 

[Gloop]

I will be buying 3 of these batteries.

http://www.pingbattery.com/servlet/the-18/60v-10ah-lifepo4-lithium/Detail

Sorry all these terms are really confusing to me, i thought connecting batteries in parallel would be easy.
Where can I find definitions for P, C, sense, and B leads?

 

[dnmun]

why not just ask ping to build a 60V 25Ah pack for you if you really don't know this stuff. first figure out where you can carry so much battery. it may even make more sense to build it as 72V 20Ah. charge to 87V DC.

ask sun-thing28 guy also if he can build you a 72V20Ah pack. it may be about 40-50% less with surface freight shipping.

 

[Gloop]

I used to own a 30Ah 48V battery from ping and i had an end-cell die, i had to open it up and solder new pouches in,
so i am wary of having 1 large pack on tour. With 3 packs, if one fails I still have 2 backup.
I am going on a tour so will have the 3 60V batteries in my trailer.
My other option are two 48V20Ah Allcell.
I live in Victoria so Ebikes.ca is just across the water in Vancouver.
So maybe the warranty will be better with allcell if something dies.

 

[dogman dan]

I agree with that, for touring you want two packs. If for no other reason, because two 5 amps chargers will charge faster than one 5 amps charger. Assuming you have something like that to charge.

I saw no need to parallel at all, if each pack is 15 ah in size or more though. On a tour, I was generally looking to hit about 350w draw averages to make range. Long gaps between towns around here.

For touring, I'd love to have two satiators. 16 amps flowing, get full in about 2 hours. I got so tired of waiting 4 hours by some plug. Better still, would be just having enough battery to go all day, then camp near a plug. That usually would mean paying for a campsite though.

 

[Gloop]

When i did my tour to calgary i used 48V30Ah, 48V10Ah, and 48V9Ah. A full charge would take 3.5 hours if i drained the big battery first.

This tour i'm hoping to get three 60V10Ah, with 3x7.5Ah Chargers. That means full in just 1.3 hours. Very little waiting.

I looked at Sunthing28's 48V15Ah packs, they are very cheap, but the chargers look flimsy and i'm not sure how easy it is to get support to replace BMS/pouches in case of failure. With the Ping i know i've replaced a BMS and pouches before, it is not that difficult and I trust Ping's support.

Same thing will AllCell, they are about 15% more expensive than Ping, but lower C rate and charge takes longer. On the 20Ah pack it takes 2.7 hours with a Satiator.

 

[ecycler]

I want to connect three 60V10Ah batteries in parallel. Can I just use two of these wires?
http://www.ebikes.ca/shop/ebike-parts/wiring-accessories/dualbattcable.html
I'm going to be doing a tour and want the 3x60V as my main battery, with a 48V10Ah as a reserve.
Or do I need to use diodes?

After reading the rest of your posts, yes. You can use two of those harnesses without diodes. You will probably be better off in the long term learning how to make your own harness by ordering wire, anderson PPs, and a crimper, though, as it will cost about the same. Are you going to be holding the batteries in the trailer and running them to your controller on the bike via a long harness? If so, you will likely want larger than 12AWG if you are pulling decent amps up long hills.

 

[mkaaskh]

Hi Everyone!

-And sorry for hijacking the thread

In short, I have two identical 48v 20ah Lifepo4 batteries (http://shop.crystalyte-europe.com/product.php?productid=16581&cat=267&page=1) that I want to connect in parallel, so I get more range. I have searched the forum and found that there is a possibility that a parallel connection like that will cause problem with both charging and discharging.

I will be charging the batteries with two chargers, but I would really hate to disconnect the batteries every time I am charging them. Is there a solution to have both the batteries still connected to the controller while charging. As I read in this thread that, that might cause problems?

As of discharging, I read somewhere on the forum that this also could be a problem, but that some diode might fix the problem? I also read that there might not be a problem, if the BMS was protecting itself enough. Therefore I have found my way the one of the BMS and posted the picture below

I know it's not the best picture, and it might not be enough to tell if the BMS is protected enough, but as you might see, the screws is glued at the head to make it more difficult to take apart. My hope was that someone could identify the BMS and tell what type it was, and if the parallel would work without the diode. If not, I will try to take it more apart and take some more pictures.

So in short short:

Is it possible to connect my batteries in parallel and charge/discharge without disconnecting any of the batteries, Thanks!

 

[dnmun]

diodes should not be used. if you do not wanna disconnect the two packs while charging then use a big switch but if you leave them connected while charging then there is no HVC protection during charging. don't know how many times i have to say it.

but i do charge both of my 21S lipo and 24S lifepo4 packs together in parallel to 88.2V without disconnecting the P- leads since it is hard wired. i can do this because the charger can only charge my packs at about 17A max and so for a 120Ah pack the charge rate is slow and i have a large 375mA balancing current for the lifepo4 so it remains closely balanced.

so if the pack is already balanced and stays that way it is possible but when balancing the first few times or when severely imbalanced they should be disconnected at P-.

 

[mkaaskh]

Ok thanks, no go on parallel while charging :/

I know you wrote that diodes should not be used, but does that mean that parallel is also a no-go when discharging (when I ride)?

 

[dogman dan]

Pardon me for being so dumb.

To parallel for discharge, you connect the P- of one pack to the P- of the other. And connect the B+ to the B+ of the other. Just a jumper wire sort of thing, that connects the bms's right?

But then where do you discharge from? From either packs discharge plug? From a plug that parallels both discharge plugs? From those jumper wires that connects the packs?

Disconnect to charge seperately, if you have a separate charge plug, got that.

 

[dnmun]

i made the observation that the packs have to be isolated while they are balancing because the charging current can be diverted around the BMS turned off for HVC on one pack and allow the pack to be overcharged.

but if the packs are charged up together after they become balanced then it is not really an issue. it really is most critical when the pack is new and has to be balanced to full charge the first time. after that the packs should remain closely balanced until allowed to sit for long periods where the self discharge on one channel would bring it outa balance again.

like i said, i have my 21S lipo pack in parallel with my 24S lifepo4 pack and i charge my lipo pack to full charge at 88.2V even though that is 1.8V higher than the balancing voltage of the 24Slifepo4.

so my lifepo4 is pushed higher by being charge through the drains of their BMS but i have a lotta balancing ability and my lipo charger is only 6A and the 11A from the charger of the lifepo4 is turned off because it is set to 86.4V.

so my lifepo4 is pushed up to 3.67V average even as it is balancing and smoking hot but that allows me to keep them hard wired in parallel and able to fully charge before i use the pack.

so what i am saying is that it really is ok to keep the them hardwired in parallel if you know they are balanced and don't have one pack that ends up going to HVC in front of the other pack. they should all charge up together and none hit HVC at all after the packs are balanced.

 

[dogman dan]

Ok, Understand that better. Likely I'll be wanting to charge separate anyway to get a charge out on the road faster. Most of the time I'll run them as separate packs. Only when needing 70 mile range will I parallel them, or if I run the gigantic cargo bike that has 40 amps controller.

But I'm still confused, not quite understanding how to do the discharge once the packs are paralleled at P- and B+.

Both discharge wires? or just the discharge wire from one of the packs? Seems like just hooking up to either pack would work, but which way is best?

 

[dnmun]

yes, both batteries would be connected at the P- and B+ and they can be connected and charged together at C- after the packs are balanced at full charge.