# Wiring a switch for series out AND parallel in??



## kcgolfer816 (Mar 9, 2014)

I want to wire a switch (or switches), two batteries, a controller, and a charging port. The batteries need to output in series to the controller and switch to parallel for charging. Trying to avoid the hassle of disconnecting/connecting every time they need to be charged. A simplistic and well labeled diagram would be very helpful.


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## Frank (Dec 6, 2008)

You could probably do what you want to do with a couple of appropriately sized relays but depending on how much current you need to handle this might be pretty expensive. Sorry, I'm not going to explore this any further for you. If something messes up you could let the smoke out of something... might be easier to wire with appropriate connectors and do it manually.


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## dougingraham (Jul 26, 2011)

To do this you need one contactor that can handle drive current levels. This contactor goes between the batteries on the positive terminal of the most negative battery and the negative terminal of the other. It is energized only when you are driving the car and is the only contactor of the three energized when driving. You also need two contactors that can handle charging current levels. One of these connects the positive terminals of the two batteries and the other connects the negative terminals of the two batteries. These should only be energized when charging.

That said this is a bad idea because when something goes wrong you short out a battery. Your best bet is to do it the right way and get a charger that can handle the higher pack voltage. Put the several hundred dollars you will spend on contactors towards a better charger.


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## crackerjackz (Jun 26, 2009)

It is also doable with diodes ... Meaning voltage can only go into the batteries and not out . But the y have to be rated to the right amperage ect ... I looked into it on my motocross charger but it was cheaper to buy 2 x 24 volt chargers and separate the pack in two for charging . But i did realize only 2 weeks ago that when charging my 12 volt system goes bazerks ... Gonna have to verify that before something goes wrong ...


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## Tesseract (Sep 27, 2008)

kcgolfer816 said:


> I want to wire a switch (or switches), two batteries, a controller, and a charging port. The batteries need to output in series to the controller and switch to parallel for charging. Trying to avoid the hassle of disconnecting/connecting every time they need to be charged. A simplistic and well labeled diagram would be very helpful.


Very dangerous if you don't time the switches just right, but here you go:


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## EcoReality (Mar 10, 2014)

You can do it with four rectifiers. I don't have time to fire up a CAD program to paint a pretty picture.

The positive side of two diodes go to the positive side of each battery, and the negative sides of those diodes connect together to the positive side of the charger. The negative side of two more diodes goes to the negative side of each battery, and the positive sides of those two diodes connect together to the negative side of the charger.

Make sure the diodes can handle the full charging current.

I'd try it with AA NiCds first -- less "magic smoke" to waste if something screws up...


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## kcgolfer816 (Mar 9, 2014)

Thanks for the suggestions so far. Honestly, I thought this would be more common and straight forward. Let me give some more details regarding the project. This will be for my kid's electric dirt bike running on 4x 5000 mAh 6s 20C batteries. First, i would pair them in parallel for 2x 10,000 mAh 6s. Next, connect those to a 4 pole 1-0-2 rotary cam switch. The switch should allow me to output the following for each of the 3 outputs: 1= series to the motor at 10,000 mAh 12s, 0= open circuit, 2= parallel to a charger. Any and all constructive input is welcome.


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## Frank (Dec 6, 2008)

Why not use a 12s balancing charger? If you need to bulk charge quickly I.e. without balancing that could also be done but there are several 12s chargers out there which would do the job. Or did I miss something?


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## EcoReality (Mar 10, 2014)

A 10A cam switch sounds expensive.

All you need are 8 10A rectifiers. Attach the + side of half the rectifiers to each battery +, and tie the - side of those rectifiers together, to the + side of the charger. Do similar, with opposite polarity with the remaining four diodes, four batteries, and the - side of the charger.

You can get these at Radio Shack, or from DigiKey for a quarter of RatShack prices.

The advantage is that there is no switching in the high-current series path. Diode commutation happens in the low-current charger path, where you can probably adjust for the ~1.2 volts the diodes are going to take away.


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## Caps18 (Jun 8, 2008)

I always thought someone would come up with a way to do this while using multiple chargers in order to fast charge a big battery pack.


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## EcoReality (Mar 10, 2014)

I don't think there is any performance advantage to parallel charging. You can't really charge any faster, and 24 6V chargers cost more than a single 144 V one.

The only practical advantage would be elimination of a battery management system for liths on nickel batteries, since they are touchy to individual cell differences.


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## Casper10 (Mar 8, 2014)

kcgolfer816 said:


> I want to wire a switch (or switches), two batteries, a controller, and a charging port. The batteries need to output in series to the controller and switch to parallel for charging. Trying to avoid the hassle of disconnecting/connecting every time they need to be charged. A simplistic and well labeled diagram would be very helpful.


What about purchasing a series parallel switch from a truck or bus they supply 12v to cabin,lights heater etc and 24v to starter circuit.


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## Tesseract (Sep 27, 2008)

EcoReality said:


> ...
> All you need are 8 10A rectifiers. Attach the + side of half the rectifiers to each battery +, and tie the - side of those rectifiers together, to the + side of the charger. Do similar, with opposite polarity with the remaining four diodes, four batteries, and the - side of the charger.....


Setting aside for a moment the question of whether your scheme needs 4 or 8 diodes, it won't work without a switch in between the two batteries to break the series connection.

With said switch present, only 4 steering diodes are needed, but since the OP already has a 4 pole switch he can use it to safely implement the scheme I proposed earlier.... as long as all the contacts can handle the current drain during discharging and are "break before make" (but even if "make before break" he has three positions so he could use one of the poles (or all three in parallel) in the first position to make the series connection of the two batteries and two of the poles in the third position to make the parallel connections.


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## EcoReality (Mar 10, 2014)

Tesseract said:


> ... it won't work without a switch in between the two batteries to break the series connection...


Yea, I just sketched it out, and I see what you mean.

You COULD do it with nothing but rectifiers if you add them in series with the batteries, but that would be in the high-current path and would drop the pack voltage by the forward voltage drop of the rectifiers.

All this "break before make" stuff is a bit scary. Here's yet another thought: why not simply put Anderson Powerpole connectors on the batteries, and make a "spider" to attach them all in parallel to the charger? Unplugging the batteries and plugging them in to the charger seems safer and only slightly less convenient than a switch that could cause a short.

I don't like switches in high current paths. But I try not to take it personally when other people insist on it.


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## kcgolfer816 (Mar 9, 2014)

Thanks for all the help! Although a switch maybe costly, I don't mind paying for a convenience that doesn't greatly sacrifice safety. This is, after all, going on a kids toy. So, safe and reliable convenience means more time playing with it. A tangled web of connectors being connected/disconnected is not something I wanna deal with several times per week. 

@EcoReality - I like your suggestion of using rectifiers, but have some questions. Will it work if they are in the parallel connection between the charger and the batteries? Would the ~1.2 volts taken away by the diodes only slow down (albeit only slightly) the charging process? Or would it take away from the top end of the charging voltage? Would I need a simple On/Off switch in the series line to the controller? Simply, installing rectifiers in the charging path and slowing the charge seems to be the least complicated and problematic solution.


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## Tesseract (Sep 27, 2008)

kcgolfer816 said:


> ... I don't mind paying for a convenience that doesn't greatly sacrifice safety. This is, after all, going on a kids toy. So, safe and reliable convenience means more time playing with it...


Oh, you want SAFE and CONVENIENT and DON'T MIND PAYING FOR BOTH? Then leave the pack connected in series all the time and buy the right charger for it, simple as that. Why muck around with switches and diodes, especially since if you forget to throw the switch to parallel before connecting the charger you will - most assuredly - cook it. The charger, that is.


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