batteries

[bigheadted]

i wish to connect a 110ah battery in parallel with a 85ah battery for use in a motor caravan, is this a good idea can you see any problems with the charging and discharging cycles if so are these safety issues and how can i get round them (i am an electrician)

 

[itsmoked]

Generally this would be considered non-optimal but doable.
Usually the same age, size and model would be preferred.

But in parallel you can do it. You will likely experience reduced lifetimes on one or both batteries though possibly not a big difference based on a dozen variables.

If you were going to series them then this would be a large no-no.

Keith Cress
Flamin Systems, Inc.-

http://www.flaminsystems.com

 

[zappedagain]

Keith makes some good points. What about wiring a disconnect switch in series with each so you only have to work with one at a time? There are lots of options:

http://www.jcwhitney.com/autoparts/...-0/showCustom-0/N-111+10201+600000926/c-10101

My buddies with their campers like this trick. That way if they drain a battery too low to start the engine for the return trip they can flip to the fresh battery.

One word or caution - don't flip the switches when the engine is running! The alternator will put out a much higher than normal voltage for a while when the battery is disconnected. The automotive electronics are designed to handle this a few times...

 

[MacGyverS2000]

Load dumps are baaaaaaad.....

Dan - Owner

http://www.Hi-TecDesigns.com

 

[VEBill]

This has been discussed before.

There are purpose-built gadgets to allow the alternator to charge both batteries while keeping the high current engine start battery isolated even if the deep cycle battery has been run down overnight.

Simplest solution is simply to purchase and install the purpose built gadget (almost certainly available from your local caravan dealer).