Inter-bike charging

[Cisco-man]

My wife has piddly Swytch battery packs whilst I have plenty of capacity in my Yose pack.

I’m thinking of making up a jump lead that goes from the power output socket of my battery, and connects to her charge port on the Swytch battery - for when we are out and about. All I need to add is a current limiter so that I don’t exceed 2A.

Ebay has various circuit boards that’ll do the trick so I’m now seeing which current limiter is the smallest/cheapest.

Any thoughts?

 

[Bikes4two]

..... Any thoughts?

Yes ---- EEK!

Do a google search on Constant Current/Constant Voltage (aka CC/CV) which is how lithium batteries are charged.

 

[saneagle]

My wife has piddly Swytch battery packs whilst I have plenty of capacity in my Yose pack.

I’m thinking of making up a jump lead that goes from the power output socket of my battery, and connects to her charge port on the Swytch battery - for when we are out and about. All I need to add is a current limiter so that I don’t exceed 2A.

Ebay has various circuit boards that’ll do the trick so I’m now seeing which current limiter is the smallest/cheapest.

Any thoughts?

All you need is an adjustable charge controller. There are many similar ones to this.

Pardon our interruption...

It's still going to take a couple of hours to get any meaningful charge into her battery.

 

[Az.]

Why won't you just buy proper battery for your wife?

 

[matthewslack]

My wife has piddly Swytch battery packs whilst I have plenty of capacity in my Yose pack.

I’m thinking of making up a jump lead that goes from the power output socket of my battery, and connects to her charge port on the Swytch battery - for when we are out and about. All I need to add is a current limiter so that I don’t exceed 2A.

Ebay has various circuit boards that’ll do the trick so I’m now seeing which current limiter is the smallest/cheapest.

Any thoughts?

Chargers for 36V lithium ion batteries output 42V, so the BMS may just say no.

If the BMS effectively allows a direct connection, then the current flowing will depend on the state of charge of the two batteries. Could be rather high, might just blow fuses if present, or might destroy things.

Short answer: don't do it!

 

[Cisco-man]

So the concensus is - bad/poor idea!

Fair enough. I spend my life thinking up solutions for problems that don’t sometimes exist.

 

[sjpt]

How about a tandem?

 

[saneagle]

So the concensus is - bad/poor idea!

Fair enough. I spend my life thinking up solutions for problems that don’t sometimes exist.

It's dead easy to fit another battery to that bike - just two wires. You can fit any battery you want wherever you want to get whatever range you want.

 

[Cisco-man]

Yes, my bike has a Yose down-tube pack, a Swytch handlebar battery holder for a Swytch gen 3 pack, and a connector on the rear pannier to take some swytch gen 2 packs that I got off my brother! I can use all three simultaneously if I wish, to get me unheard of distances!

It’s just my wife won’t let me modify her bike, and in her words, over-complicate it - as if I would…

 

[Az.]

It’s just my wife won’t let me modify her bike, and in her words, over-complicate it - as if I would…

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[Bikes4two]

...... I can use all three simultaneously if I wish, to get me unheard of distances!
…

Out of interest when you say 'simulataneously' do you mean running the batteries together in parallel, or just using them sequentially as in when one is discharged you disconnect and plug the other one in?

If running in parallel, do you 'join' them together with some clever 'box of tricks' or just after careful voltage measurement?

 

[Cisco-man]

Out of interest when you say 'simulataneously' do you mean running the batteries together in parallel, or just using them sequentially as in when one is discharged you disconnect and plug the other one in?

If running in parallel, do you 'join' them together with some clever 'box of tricks' or just after careful voltage measurement?

In parallel. I isolate each pack with part of a MR30 shottky diode. Very little voltage drop (around a quarter of a volt). I can slap on a quick and easy swytch gen 3 pack for going down the shops, or add other packs to go further. The beauty of multiple packs is that I don’t get significant voltage slump when going up hills as the draw on each pack is reduced. Obviously the pack with the most charge will predominate until the voltages are level.

 

[Bikes4two]

No Thanks for that @Cisco-man. I had thought of doing something similar with shottky diodes and had also started to look at 'ideal diodes' too as their forward voltage drop is even smaller, but haven't really got around to giving it a go.


Another winter project I suspect .

 

[matthewslack]

No thanks for that @Cisco-man. I had thought of doing something similar with shottky diodes and had also started to look at 'ideal diodes' too as their forward voltage drop is even smaller, but haven't really got around to giving it a go.


Another winter project I suspect .

I use the same technique for my solar trailer. If you use simple and quick connectors both on the diode setup and bike wiring it is quite a small job, and the diodes can be added/removed 'in an instant'.

Hint: run a three ended 'black' cable as well as the 'red' three legs of the diode, so every connection is simply a +/- pair.

 

[Bikes4two]

....... Hint: run a three ended 'black' cable as well as the 'red' three legs of the diode, so every connection is simply a +/- pair.

Er, sorry for being thick, but I don't understand the above .

 

[matthewslack]

Er, sorry for being thick, but I don't understand the above .

I'll post a picture tomorrow.

 

[matthewslack]

I'll post a picture tomorrow.

Like this:



Two, two way input connectors on the left, one, two way output connector on the right.

I just unplug the battery cable, insert this, and good to go, solar or not. The bike wiring does not need any modification if a convenient connector already exists.

The negative wiring does nothing except make the connection and switch from one to two batteries easy.

Backing board and cable ties for mechanical support. Cooling not needed as I run very low in the diode's capabilities.

 

[Ghost1951]

I have never done this, and hesitate to jump into a discussion with people who have, but I am a bit worried that someone with no knowledge might read this thread and unwittingly connect two battery outputs together in parallel without isolating them as regards one charging the other. My concern is that if those batteries are not at the same level of charge, say one is low and the other not, you would get a very large flow of current from one to the other. This is pretty dangerous if done like that. It is not only the well informed battery folk who could read this. The completely naive can find it too. I have heard of fires caused by paralleling batteries badly. I know no one has suggested that, but maybe a warning is needed not to just connect un-alike battery outputs together.

Am I wrong? Maybe I am.

 

[guerney]

Like this:

View attachment 58238

Two, two way input connectors on the left, one, two way output connector on the right.

I just unplug the battery cable, insert this, and good to go, solar or not. The bike wiring does not need any modification if a convenient connector already exists.

The negative wiring does nothing except make the connection and switch from one to two batteries easy.

Backing board and cable ties for mechanical support. Cooling not needed as I run very low in the diode's capabilities.

Thanks for posting about this. Which diode do you use? You may have mentioned it before on one of your solar trailer adventure threads, but I can't recall.

While you're here, how many solar panels would I need to power 100 of these to make an atmospheric water harvesting system for my off-grid garden?

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[Bikes4two]

Connecting battery at .............. - I have not tried or seen anyone doing it.

Then maybe for safety's sake you should delete your post rather than even begin to make the suggestion?

Just saying.