Adding a second battery where do I put the inverter wires

Cockers

Cockers

Joined
Jul 15, 2015
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Location
Isleham Cambridgeshire
Funster No
37,170
MH
Autotrail Dakota
Exp
Since 2012
Good morning all,
I have decided to add an additional battery to the Autotrail so I have purchased a Battery harness from Sergent, basically because it just plugs in and works.
My question is : do I leave the inverter connections on one battery or do i put the positive on the first battery and the negative on the second battery so it draws equally from both. I am replacing the old battery with two new 110Ah Batteries.
Any advice greatly received, as im a but thick when it comes to electrics
Thanks
 
How big is your inverter? yes it should be connected to both batteries but if you add the second battery with the battery harness you will be pulling 50% of the inverter draw through some fairly skinny looking cables.

Martin
 
The general rule if you have 2 batteries is to use the +ve off one battery and the -ve off the second battery. As far as everything i have very read and thats how i have mine. (y)

Ref the Sargent harness, No issues using these. My past 2 vans had them fitted with 2 batteries and all good.
 
Thats great thanks for your help, regarding the wiring from the inverter to the battery i used heavy duty cable its about 10mm thick and only runs a short distance, about 18" from battery to inverter.

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Just looked at that Sargent battery harness, the cables are way undersized for connecting a battery in a Motorhome. they look about 4 -5 mm sq, they need to be at least 16 mm sq.
 
In theory, for two batteries, put inverter positive to one battery and inverter negative to the other battery, as you said. The links between the batteries need to be at least half the area (in square millimetres) of the inverter wires. Usually people just use the same wire for the links as for the main inverter cables.

I'd guess the Sargent links are a bit thin for this purpose, so you'd be better beefing them up a bit.

Edit: I see the inverter is only 600 watts, so maybe the Sargent harness will be adequate.
 
Last edited:
Lenny HB said:
Just looked at that Sargent battery harness, the cables are way undersized for connecting a battery in a Motorhome. they look about 4 -5 mm sq, they need to be at least 16 mm sq.
Click to expand...

They are thin but match the rest of the van wiring..
Had 2 x apache 700 in past 12 years. Both had these additional harness fitted. 2 x 110amp batteries and my 600w inverter attached direct to batteries. In both vans never an issue, EHU and solar charge was always fine.

A socket is fitted ready to accept the harness and wire size from the PSU / Charger unit is same size as the harness.
 
tonka said:
They are thin but match the rest of the van wiring..
Had 2 x apache 700 in past 12 years. Both had these additional harness fitted. 2 x 110amp batteries and my 600w inverter attached direct to batteries. In both vans never an issue, EHU and solar charge was always fine.

A socket is fitted ready to accept the harness and wire size from the PSU / Charger unit is same size as the harness.
Click to expand...
With undersized cables you are always going to get volt drops so equipment operates inefficiently. There have been quite a fun posts on Fun over the years about Autotrails with Truma combi's shutting down due to low voltage because of the volt drop.

A neighbour has an Autosleeper with silly size wiring after talking to me he rewired the van with sensible size cables. :D

Also the stupid undersized wiring in Brit van is one of the reasons you never get a decent charge rate from the split charge relay and fridges perform poorly on 12v.

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If I disconnect both batteries to beef up the connecting wires for the inverter what should I do with the connection to the solar panels during the change. Assuming it is daylight there will be some current from the charging circuit?
 
With such a small inverter and the batteries close together its not likely to matter if connection is to only one battery, because of location my 1500w inverter is only connected to one battery and works fine. Very heavy wiring though.
 
Lenny HB said:
With undersized cables you are always going to get volt drops so equipment operates inefficiently. There have been quite a fun posts on Fun over the years about Autotrails with Truma combi's shutting down due to low voltage because of the volt drop.

A neighbour has an Autosleeper with silly size wiring after talking to me he rewired the van with sensible size cables. :D

Also the stupid undersized wiring in Brit van is one of the reasons you never get a decent charge rate from the split charge relay and fridges perform poorly on 12v.
Click to expand...

All I can say is that it worked ok for me and never any issues in my Autotrail days...

HOWEVER... I am now a BURSTNER owner so its all in the past.. (y) :whistle2: :rofl:
 
Thanks everyone for your comments, im looking at up grading the whole system in a coulpe of years i'd like to up grade the solar panels 3 x 150 and batteries for lithum to make the van a bit better off grid. hopfully it will be okay for a few years.
 
tonka said:
The general rule if you have 2 batteries is to use the +ve off one battery and the -ve off the second battery. As far as everything i have very read and thats how i have mine. (y)

Ref the Sargent harness, No issues using these. My past 2 vans had them fitted with 2 batteries and all good.
Click to expand...

Yep Take the output from the outer terminals and feed the charging into the batteries into the centre terminals

battery wiring.jpg

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Mr Chrysalis said:
If I disconnect both batteries to beef up the connecting wires for the inverter what should I do with the connection to the solar panels during the change. Assuming it is daylight there will be some current from the charging circuit?
Click to expand...
First blank off panel/s with cardboard taped down. Then remove any fuses .
 
then check the voltage with a meter to se if you have 24v
 

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