# I am almost too embarassed to ask.



## Rod Fearnley (Jan 2, 2008)

Guys, I have it in mind to have an onboard battery, in a Loco, but would like to have the ability to have a battery car as well. What will happen if I connect a 12volt Battery to a 12volt battery + to + minus to minus? A heating issue? I don't have room for another switch in the install.
Also would the battery's have to have the same Amp Hour ratings? 

Rod


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## peter bunce (Dec 29, 2007)

Hi Rod, 

I asked the question for you on G scale mad - they say look at the following - hope it helps! 

http://www.reuk.co.uk/Interconnecting-Batteries-for-Battery-Bank.htmi 


Hope the snow is not too deep over there!


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## Del Tapparo (Jan 4, 2008)

When connected in parallel, the battery with the higher voltage (neither one will be exactly 12V) will try to charge the other one, thus wasting energy, perhaps even to the point of overheating and damage. You would need to isolate the batteries using diodes in the positive leg of each battery: battery + to anode(diode+), cathode of each diode (diode -) connected together and then on the the positive input of your control system. Negative sides of the batteries connected together. A 1N4001 diode or similar should work. 

If you had the room, you could install one of my "battery conversion module"s or one of Tony's BIK's in the loco, which allow you to run the loco solo, or plug in the trail car for extended run times on the larger battery.


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## Greg Elmassian (Jan 3, 2008)

Dell, isn't the current rating of the 1N4001 only one amp? 

I'd recommend 3 amps minimum, and personally I would use a 5 amp diode. I do understand that with 2 batteries in parallel, if they were perfectly matched that a 3 amp load would only result in 1.5 amps each, but "perfectly matched" never happens, so I always design for worst case, thus the 3 amp diode recommendation. That still would not protect from full stall current. 

Just a suggestion (and attendant reasoning) 

Regards, Greg


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## Del Tapparo (Jan 4, 2008)

Right you are Greg. I would also use 3-5 amps.


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## Bill Swindell (Jan 2, 2008)

I found a great thing for connecting 2 battery packs together.

http://www.allelectronics.com/make-a-store/item/MBR2545CT/DUAL-SCHOTTKY-RECTIFIER-25A-45V/1.html 

Hook each battery + lead to the outer leads and use the center lead to feed your receiver. This isolates the 2 batteries with a minimum of voltage loss.


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## Rod Fearnley (Jan 2, 2008)

Cheers Peter, I'll take a look, I am registered over there.

Thanks Del, I'll have a look at your BCM.
Greg as always, good advice. Thank you
Bill, most interesting. Do you forsee any problems with using it on an Airwire Rx?

Rod


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## eheading (Jan 5, 2008)

That is a great suggestion, Bill. I like that much better than the individual diodes I've been using. In fact they have a 10 amp 100V Shottky diode rectifier also that is even less expensive!

Thanks for the great suggestion!

Ed


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## Greg Elmassian (Jan 3, 2008)

Nice suggestion Bill, the lower drop of the schottky diodes should also make it so that there is no need to heat sink it, even at high currents. 

Will file that away... I buy a bunch of stuff from All Electonics, but mostly connectors. 

Regards, Greg


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## SlateCreek (Jan 2, 2008)

Depending on how you're plugging in the trail car, wouldn't a jack that disconnects the onboard batteries when there's a plug in the jack do it? 

Matthew (OV)


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## nkelsey (Jan 4, 2008)

The battery conversion modules by G Scale Graphics and by RCS both allow using the charging plug as an additional battery jack if wired that way. 

http://1stclass.mylargescale.com/DelTapparo/BCM.htm 

http://www.rcs-rc.com/index.php?page_id=1065


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## Bill Swindell (Jan 2, 2008)

Ed, I have used the shottkey diodes on several AirWire installs. It works great.


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## TonyWalsham (Jan 2, 2008)

Isn't it wonderful how great minds think alike. 

The RCS/EVO # BIK-U3 will do exactly what you want to do Rod. 
The pcb might be a bit big for most "0" scale locos but the same ciruit could be wired in by hand.


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## kcndrr (Jan 7, 2008)

Bill 
you say 
Hook each battery + lead to the outer leads and use the center lead to feed your receiver. This isolates the 2 batteries with a minimum of voltage loss. 
that covers alll four of the input leads, where do you put the two output leads to power unit. 
please be aware i am not an electrical guru. 

KC


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## Rod Fearnley (Jan 2, 2008)

Bill, will this Shottyky do the job? It is available over here in England. Link below. 

Thanks for your input Tony. 

Rod 


http://www.maplin.co.uk/Media/PDFs/Module 46429.pdf


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## Del Tapparo (Jan 4, 2008)

Yes, that part will work. As to the wiring: Connect battery no.1 + to pin 1, battery no. 2 + to pin 3, diode pin 2 to power input + of your control. Connect battery no.1 - and battery no. 2 - to power input - of your control. When making the physical connections you will have to provide some kind of stress relief on the wiring to keep from bending and breaking the leads on the diode. Maybe heat shrink tubing on each lead and then tape the whole thing up good?


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## Bill Swindell (Jan 2, 2008)

KC, Hook the two - leads to the minus input to your receiver. Hook the center lead from the diode asswmbly to your fuse and on/off switch then into the receiver.

Rod, That looks just like the diode that I was talking about. Go for it.

The key thing about using diodes is that you can draw current from both batteries all of the time. You will draw current from the battery with the highest voltage until it is eqqual with the other battery then thew will both draw down together.


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## nkelsey (Jan 4, 2008)

Tony, thanks for the compliment.... my wife says I have a one track mind, dirt track at that.


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## TonyWalsham (Jan 2, 2008)

Here is how the RCS BIK-3 circuit can be wired up using discreet components instead of the kit.


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