Switching between two batteries (48v)

[leew]

Hi, building an eTrike, and I have bought two batteries, one will go at the front under the pedal boom and one rear behind the seat to help weight distribution. My plan was to use a SPDT switch to switch between the two batteries so when one was almost flat I'd just switch to the second one. Just been looking at switches and having trouble finding one which is suitable for 48v 35a, most switches I have seen seem to be rated upto 250v but on closer inspection that is 250v ac, not dc and the DC rating seems to be only 32v for most switches. High voltage DC switches seem to be almost unobtainable. I have seen a few industrial contractors with a high DC rating but they are massive heavy looking things and only seem to be single throw, not double throw. Does anyone know of a switch I could use? As my controller is rated at 35a, a 35a switch will be ok? Is it possible to use a lower voltage/current rated switch if I only intend to operate it with the throttle at idle?

Many thanks, lee.

 

[Ykick]

Forget about high current & voltage switching. Just parallel the battery packs and drain ‘em both at the same time and rate. They’ll be much happier in the long run.

 

[leew]

Forget about high current & voltage switching. Just parallel the battery packs and drain ‘em both at the same time and rate. They’ll be much happier in the long run.

I believe if I parallel the packs I'd then need to put diodes on the discharge wires to protect them which means I won't be able to use the regen?

 

[shr00m]

an alternative would be to just wire them up and have 2 connections 1 for each battery and physically unplug and plug in the 2nd battery when the first one is done.... id recommend parallel but i think you are correct about no regen with diodes.

 

[Ykick]

Forget about high current & voltage switching. Just parallel the battery packs and drain ‘em both at the same time and rate. They’ll be much happier in the long run.

I believe if I parallel the packs I'd then need to put diodes on the discharge wires to protect them which means I won't be able to use the regen?

Where do you get the need for diodes?

Do these packs have BMS? If so, they're protected. If no BMS, the 2 parallel packs can be handled as one large pack and regen to your hearts content. Although regen is way overrated, IMO...

 

[LewTwo]

Take a look at 24 volt automotive starter relays.

 

[craneplaneguy]

I have been using these for years for all kind of DC applications, from 12 to 52 volt. They work great, and have threaded studs making it easy to attach large dia. cables, and also 1/4" hole in the base so you can securely bolt them down. Waterproof also!
https://www.zoro.com/buyers-products-automotive-circuit-breaker-cb-60a-12vdc-cb60pb/i/G6206033/?gclid=CjwKEAjwp-S6BRDj4Z7z2IWUhG8SJAAbqbF3iJUuBdn3T-U5z3qxA2FsXhM7hoKaAolSNqJ1v52tXBoCsJLw_wcB&gclsrc=aw.ds

 

[Bicycle365]

More important that protection during regen is protection when establishing a parallel connection. Both batteries MUST be the same chemistry and at the same voltage when paralleled or you risk a massive discharge from one to the other as they try to equalize. This could be anything from catastrophic failure, could trip the protection on the BMS's or just get unneeded heat into your expensive packs.

 

[KINNINVIEKID]

More important that protection during regen is protection when establishing a parallel connection. Both batteries MUST be the same chemistry and at the same voltage when paralleled or you risk a massive discharge from one to the other as they try to equalize. This could be anything from catastrophic failure, could trip the protection on the BMS's or just get unneeded heat into your expensive packs.

simple answer is to parallel charge them so they are always at the same state of charge.
I do this with 4 Multistar batteries and diodes are not needed.

 

[amberwolf]

If the packs are identical in construction, chemistry, and age, then just charge them each up to full, then wire their discharge ports in parallel and use them in parallel all the time.

That will be easier on the batteries (each sees only half the load it would have by itself), and there is less voltage sag, so you get better performance from the whole vehicle.

If you have two chargers, then leave the discharge ports separate so you can charge each pack separately / faster.


As for regen, if each pack has a charge port (to charger) and a discharge port (to controller) then it's not protected against overcharge by regen anyway. But unless you do a lot of regen braking when the pack is still full and hasn't been used, it's not going to affect anything as regen is generally short bursts.

If you have long downhills you're using regen to keep you slow on, and the regen current is a lot higher than normal charge current, there might be a possibility of problems--but these problems would actually be reduced by having the packs wired in parallel, because then only half the current goes to each pack.

 

[dogman dan]

Yes, you can parallel them without the diodes. But I think it is still best to unplug them from each other to charge them, if there is a bms.

FWIW, if you did put the diodes on, they would completely block any regen.

If they are large enough packs, just stop, unplug one, and plug in the other. Surely you want to get off the bike at some point in a ride that long, right?

 

[ddk]

... High voltage DC switches seem to be almost unobtainable.

NKK makes a -S- series switch that would work at 60V Bu-u-u-u-ut @48V most switches rated for 32V DC work fine. Bu-u-u-u-u-uT those same switches that work fine @48V will weld themselves switching, say, 60V (hence my recent search for switches that will work at 60V because I just welded these shut)

I have seen a few industrial contractors with a high DC rating but they are massive heavy looking things and only seem to be single throw, not double throw.

this same switch is available in a spdt configuration, but I'm too lazy too go out to the workshop to take a pic. I'm using pics because the switch is sold in automotive parts stores under various brand names but they seem to all be the same switch.

Does anyone know of a switch I could use? As my controller is rated at 35a, a 35a switch will be ok? Is it possible to use a lower voltage/current rated switch if I only intend to operate it with the throttle at idle?

Many thanks, lee.

Also the connector I use for my batterys(Speakon NL4) can be used as a off/on switch should you decide to use separate connections per someone's suggestion. It safely connects/disconnects up to several hundred Volts.