Parallel batteries

[vfr400]

How close do the 2xbatteries volts need to be when coonnecting up and using something like this?

Assuming normal lithium-ion batteries and assuming fully charged, I'd be happy to connect them in parallel up to 0.3v difference without that device. The difference would have to be about 2v before things start to get dangerous because that's the sort of sag you get when drawing normal current; however, it might not do the cells much good charging at 10 amps through the output terminals.

With the device, they can be anything you want, but I think my nerves would tell me to make them close before connecting.

 

[awol]

With the device, they can be anything you want, but I think my nerves would tell me to make them close before connecting.

When using these schottky diodes does current still flow between the batteries but controlled and very slowly or are the batteries electronically kept completely separate so you could just plug either one in and out to swap it whenever you want?

 

[Sturmey]

How close do the 2xbatteries volts need to be when coonnecting up and using something like this?

They dont have to be close at all. One battery can be fully discharged and the other fully charged. However (and this is very important), this is only the case where each battery individually is capable of supplying full current to the controller. So for example in my case, I often parallel my 11ah with another 13ah battery to supply a 14amp max controller to increase my range so no problems, as each battery individually can supply 20 amps peak.
A different situation exists when say someone has a huge motor with say a 25 to 30 amp controller and he has two batteries that are only rated at say 20 amp max discharge.
In this case the batteries need to be matched and similar voltage so that each supplies about 13-15amp ( or at least does not exceed 20 amps )and wont trip the bms.

 

[Nealh]

The individual components aren't my thing and understanding board layouts I find confusing, can not the single schottky diodes not work then as well like the one below. Although 6a rated is has a 300a high surge current.

6A10 Blocking Schottky Rectifier Diodes 1KV/6A 1000V | eBay

Find many great new & used options and get the best deals for 6A10 Blocking Schottky Rectifier Diodes 1KV/6A 1000V at the best online prices at eBay! Free delivery for many products!

www.ebay.co.uk

 

[WheezyRider]

How close do the 2xbatteries volts need to be when coonnecting up and using something like this?

It doesn't matter, current can't flow from one battery into the other with a diode set up.

The amount of current taken from each battery and sent to the controller will depend on the state of charge of each pack. If one is more charged up than the other, it will supply the bulk of the current until its voltage drops to match that of the other battery.

 

[WheezyRider]

The individual components aren't my thing and understanding board layouts I find confusing, can not the single schottky diodes not work then as well like the one below. Although 6a rated is has a 300a high surge current.

6A10 Blocking Schottky Rectifier Diodes 1KV/6A 1000V | eBay

Find many great new & used options and get the best deals for 6A10 Blocking Schottky Rectifier Diodes 1KV/6A 1000V at the best online prices at eBay! Free delivery for many products!

www.ebay.co.uk

You'd have to put several of those in parallel, as you're likely to draw more than 6 amps continuous through the diode if only one pack is connected, or one pack is discharged.

But you can get 100V 60A versions that do the job that are cheap enough:



The other advantage of this diode case format is that you can fit a heat sink directly on the diode, as you will consume a small amount of power.

 

[awol]

But you can get 100V 60A versions that do the job that are cheap enough:

View attachment 37530

The other advantage of this diode case format is that you can fit a heat sink directly on the diode, as you will consume a small amount of power.

Out of curiosity I want to make one of these leads, do I need 2 of these (one for each connected battery)?

 

[Woosh]

you only need one, they have two diodes in each device.

 

[Bikes4two]

......... I want to make one of these leads, do I need 2 of these ..............?

This is not necessarily directed at the OP, but to those who on reading this thread, might have similar queries, and it is this:

Given that such a question as the above and other similar questions of a very basic nature have to be asked in the first place, I would advise that caution is exercised before embarking on the making of such a lead.

Yes, we are looking at simple circuitry here, but non the less there is a level of knowledge required to safely make up such a lead which, at the end of the day, is going to be joining two high powered energy sources together.

If you have no knowledge of anodes, cathodes, heat sink installations, insulating methods and so on, then I would advocate you look at something like the device @Woosh will be selling (post #12).

 

[WheezyRider]

Out of curiosity I want to make one of these leads, do I need 2 of these (one for each connected battery)?

If you want to make a Schottky diode "Y" adaptor for running two batteries in parallel, you need a diode in each leg of the "Y" (one for each battery).

The Woosh device, you only need one, but it only uses one battery at a time and then switches over when the primary battery is discharged.

 

[WheezyRider]

This is not necessarily directed at the OP, but to those who on reading this thread, might have similar queries, and it is this:

Given that such a question as the above and other similar questions of a very basic nature have to be asked in the first place, I would advise that caution is exercised before embarking on the making of such a lead.

Yes, we are looking at simple circuitry here, but non the less there is a level of knowledge required to safely make up such a lead which, at the end of the day, is going to be joining two high powered energy sources together.

If you have no knowledge of anodes, cathodes, heat sink installations, insulating methods and so on, then I would advocate you look at something like the device @Woosh will be selling (post #12).

I agree, if you want to make a Schottky diode based adaptor and you are not sure what you are doing, get help. Don't risk blowing up two battery packs or worse...

 

[vfr400]

I agree, if you want to make a Schottky diode based adaptor and you are not sure what you are doing, get help. Don't risk blowing up two battery packs or worse...

Why don't you show him? It's not exactly difficult. He's been on this forum installing electric bike kits, etc for 7 years. He's not a dunce. That's what the forum is for.

 

[WheezyRider]

Why don't you show him? It's not exactly difficult. He's been on this forum installing electric bike kits, etc for 7 years. He's not a dunce. That's what the forum is for.

I hope I didn't give the impression I was talking to anyone in particular. I was talking generally to anyone who might be reading the thread.

 

[vfr400]

I hope I didn't give the impression I was talking to anyone in particular. I was talking generally to anyone who might be reading the thread.

My question still stands. The guy asked how to do it. Why don't you help him?

Just as an aside, we have a forum member Cwah. When he first came on the forum, he didn't know that you couldn't undo a hex screw with a flat-bladed screwdriver, but we helped him learn. He went on to make 3,000 posts and he became an innovator that we all learnt from.

 

[WheezyRider]

My question still stands. The guy asked how to do it. Why don't you help him?

Will do, just need a bit of time. Probably won't be today though, got a load of other stuff I have to deal with. I'll try and put a how to together tomorrow.

 

[WheezyRider]

Just as an aside, we have a forum member Cwah. When he first came on the forum, he didn't know that you couldn't undo a hex screw with a flat-bladed screwdriver, but we helped him learn. He went on to make 3,000 posts and he became an innovator that we all learnt from.

I agree totally. We are here to help, encourage and support each other. However, although this procedure is quite simple, it does need to be done with care as there is risk involved if it is not done properly.

So if anyone is not exactly sure what they are doing, they need to ask for help. If it goes wrong, expensive damage can result, or personal injury could occur.

 

[WheezyRider]

Will do, just need a bit of time. Probably won't be today though, got a load of other stuff I have to deal with. I'll try and put a how to together tomorrow.

Ok, here you go...

Schottky Diode Parallel Pack Adaptor

People often ask, “can I put two packs in parallel to increase capacity and reduce strain on each battery pack?” Yes you can, but you need to make sure that the two packs are of a similar voltage before connecting them. Also, if you disconnect one pack, the socket will still be live from the...

www.pedelecs.co.uk

I've put it in the technical section, as I thought that might be more appropriate.

 

[Bikes4two]

Nice one @WheezyRider - I've read the write-up and it gives folks the key points to consider.

 

[Nealh]

For paralleling any one who is thorough and makes sure voltage are very close so say
for 36v, 41.5v & 41.6v then there is no need to go down the mod route for your balance leads. Stick with the routine you already know and are happy with rather then go down the that will do road.

 

[vfr400]

For paralleling any one who is thorough and makes sure voltage are very close so say
for 36v, 41.5v & 41.6v then there is no need to go down the mod route for your balance leads. Stick with the routine you already know and are happy with rather then go down the that will do road.

This is the approach I've always taken. It's no big deal to charge both batteries before connecting. Why would you want to use a half-charged one if you're going on a journey that needs two batteries?