charging two batteries in series

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Benjamin Maggi
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charging two batteries in series

Post by Benjamin Maggi » Wed Feb 20, 2019 3:25 pm

My Plum Cove engine uses two 12v batteries wired in series to provide 24 volts. To recharge the batteries I have a Battery Tender 24v, 2.5 amp model (022-0158-1). It doesn't trickle charge batteries but maintains them at 26v. I admit I don't know the difference.

I purchased a steel replacement body and want to make it easier for my wife to use the engine, so I would like to set it up so that the charger can be connected to the batteries without having to remove the body. Is there a way to wire the engine so that the batteries are connected to the control board, but also the wires can lead to a plug or something which can be connected to the output of the battery charger? Would it be safe to use a toggle switch, or is there a better way?

Hundreds of these engines are out there, so it must be possible.

Thanks.

For what appears to be the same discussion (though it involved a different chassis):
viewtopic.php?f=33&t=96734&hilit=battery+tender+charger
"One cannot learn to swim without getting his feet wet." - Benjamin Maggi
- Building: 7.25" gauge "Sweet Pea" named "Catherine"

rkcarguy
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Location: Wa State

Re: charging two batteries in series

Post by rkcarguy » Wed Feb 20, 2019 3:53 pm

The battery tender brand offers a pigtail that you can bolt onto the batteries, with a rubber connector plug that should match the one on your battery tender charger cords (assuming you have alligator clips that plug into your charge cord). Zip tie it up in a convenient place, and you're set.
I have these on pretty much everything I own with a battery that spends time sitting. A local motorcycle shop should have these on hand, or you can order it.

https://www.amazon.com/Battery-Tender-0 ... X4Z24W1JZC

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Benjamin Maggi
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Re: charging two batteries in series

Post by Benjamin Maggi » Wed Feb 20, 2019 3:59 pm

Humm... I think mine came with that rubber connector plug. Thanks.
"One cannot learn to swim without getting his feet wet." - Benjamin Maggi
- Building: 7.25" gauge "Sweet Pea" named "Catherine"

rkcarguy
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Joined: Tue Aug 22, 2017 10:33 am
Location: Wa State

Re: charging two batteries in series

Post by rkcarguy » Wed Feb 20, 2019 4:11 pm

I have a larger battery tender that did come with the pigtail, and a little wall-wart one that did not.

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DianneB
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Re: charging two batteries in series

Post by DianneB » Wed Feb 20, 2019 5:53 pm

The only thing with charging batteries in series is that they must be well matched - same make, same size, same age, and always used in series. Otherwise the charge will not be balanced. It is a good idea to periodically check the battery voltage after use with a digital voltmeter to make sure they are within 0.1 volt of each other.

I use two 12 volt batteries in series in my streetcar but periodically one or the other gets "borrowed" to use in something else so I always charge them with two 12 volt chargers. One day I plan to put a 3-pin connector on the streetcar and use 2 separate battery maintainers (at the same time).

John Hasler
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Re: charging two batteries in series

Post by John Hasler » Wed Feb 20, 2019 6:25 pm

You can equalize your batteries by connecting them in parallel and charging them that way. As Dianne says, though, they must be well matched. Once equalized they can be charged and discharged in series.

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Erskine Tramway
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Re: charging two batteries in series

Post by Erskine Tramway » Thu Feb 21, 2019 10:38 am

I use the Battery Tender double charger on Sparky. It is pricy, but will keep the combined batteries in the 27 volt range.

https://www.amazon.com/Battery-Tender-0 ... ery+tender

The pigtails come down into the tool box below the running boards, where you can see the leads in this picture.

PICT0054.jpg
Mike
Former Locomotive Engineer and Designer, Sandley Light Railway Equipment Works, Inc. and Riverside & Great Northern Railway 1962-77
BN RR Locomotive Engineer 1977-2014, Retired

SCBryan
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Re: charging two batteries in series

Post by SCBryan » Thu Feb 21, 2019 12:29 pm

On my interurban, I use four deep cycle batteries. Each pair is wired in series and the two pairs are connected in parallel to supply 24 volts to the controller. I wired each battery through a set of relays. Under the car, I have a toggle switch that pulls the relays in for charging, effectively changing them all to parallel. There are two brass studs under the car (energized at 12 volts when the relays are activated) to which I attach a standard 12V Automotive charger. I usually apply the charger over night to attain a full charge. This has worked well for me for over ten years. Note that when necessary, I replace all batteries at the same time and make sure they are all the same age.

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