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Badger110

Member Since: 06 Feb 2018
Location: South hams
Posts: 1025

2011 Defender 110 Puma 2.4 USW Buckingham Blue

Voltage increase

Installed the Webasto air top and as a precaution I ran a multimeter across the aux battery whilst it was running ang got 12.14v

When I switched it off and it ran through it’s shutdown cycle, the voltage began to increase up to 12.38v.

My set up is;

Main battery > VSR > Aux battery > Aux fuseboard > Webasto, lights, sink etc.

Is the increase due to power being drawn from the main battery?

I understand the vsr allows power from the main battery\ alternator when 13.8v is registered to pass to the aux to charge it, so I’m not expecting an increase in voltage from the main battery.

Is it just the battery voltage setting when it has no draw on it?

Cheers

2nd Jan 2019 6:01pm

BenB8man

Member Since: 22 Mar 2017
Location: Norfolk
Posts: 427

2010 Defender 110 Puma 2.4 DCPU Stornoway Grey

I'd say that it settling is a fair guess. You'll find batteries move around a bit like that. If you left it all running you probably would have found the battery would increase/recover its voltage even at the same current draw too.

2nd Jan 2019 7:00pm

Badger110

Member Since: 06 Feb 2018
Location: South hams
Posts: 1025

I was hoping that'd be the case.

My only fear is the aux battery is drawing power from the main starter battery, which i don't want!

2nd Jan 2019 11:04pm

leeds

Member Since: 28 Dec 2009
Location: West Yorkshire
Posts: 8578

A 12 volt battery showing a rested voltage/no load showing 12.38 volts is about 70-80% fully charged. OK it does depend on the accuracy of the volt meter

Now a light load on a 12volt battery will drop the apparent battery voltage by about 0.3 volts, whilst a heavy load could drop the apparent battery voltage by around a 1 volt plus.

Once the load is removed the voltage of the rested battery will rise to represent its state of charge. which on your figure is about 70-80% charge.

Hope that makes sense.

Brendan

3rd Jan 2019 12:33am

Badger110

Member Since: 06 Feb 2018
Location: South hams
Posts: 1025

Cheers Leeds

3rd Jan 2019 7:50am

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