DIY : Dual battery

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HBannink
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Re: DIY : Dual battery

Thu Mar 24, 2011 11:36 pm

4ePikanini wrote:Jip. I'm lucky. The previous owner's existing cables are about the size of a citi golf's starter cables so I'm sorted there to charge the 2nd battery (I have checked and only get 0.1v drop over the length)

From there I cut the supplied cables for the inverter and connected them to the 2nd battery via new terminals so they are properly secured with a good connection.

I just need to figure out how to go from the inverter's supplied 2 point feed to a 3 point plug - my only gripe with the inverter because it doesn't give a standard 3 pin plug.
Voltage drop under no load situations would be negligible but where it matters is at full load. The higher the amperage drawn the greater the voltage drop resulting in mote current being drawn to compensate for the drop in voltage and so it runs in a vicious circle. At a foll load of 67 amp on the battery side I would go no less than 16mm and for safety sake 25mm but judging by your description of the existing cable it sounds fine. For peace of mind ensure that there are two cables going to the back, some folks just take a live and use the chassis as negative.

The third point in your plug is the earth and would normally be taken from the casing of the inverter and connected to the chassis as well, problem is you can still get a nasty surprise if you have a leak as the vehicle is stood on rubber so there is no real earth to speak of and it is possible to get an elevated voltage from the casing. I have often heard of this kind of situation and have a 1500w inverter lying here that energises the casing to 170v, needles to say his unit lies in the store waiting for a turn in the repair dept. Personally I would not connect the third line and if you feel any tingling sensation from the vehicle while the inverter is on, have it seen to before it becomes a shocking experience :twisted:


Henk Bannink

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4ePikanini
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Re: DIY : Dual battery

Fri Mar 25, 2011 6:46 am

Thanks for the tips

At the moment there is two cables running to the back of the pajero from the battery. They will be used solely for charging the second battery.

The cables from the second battery to the inverter are the ones supplied with it but they are now shorter and have better connections to the battery than the supplied crocodile clips.

The inverter is bolted to a plastic toolbox and the toolbox sits in the pajeros plastic compartment where the 3rd row seats are now.

I have alsso thought that I'm not going to connect a ground on the 3 pin plug as the inverter doesn't supply one and many appliances these days only come out with the 2pin plug

My intended use for this is to supply my tv in case of power failures - I won't get much time heh?..... And to charge laptop and camera etc on trips where there is no 220v
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Re: DIY : Dual battery

Fri Mar 25, 2011 8:06 am

If I read Marius's diagram correctly, he proposes to use a DC-DC charger.
For that application, the wire thickness can be reduced to suit the the max. current draw of the DC-DC charger.
5 sq mm will most probably do it.

Voltage drop for this application is immaterial, since the DC-DC charger works on a range of input voltages (eg 10.5V-18V).
The fuse on the cables can also be so much smaller.

That is the beauty of the DC-DC charger.
Gerhard Fourie
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4ePikanini
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Re: DIY : Dual battery

Fri Mar 25, 2011 8:13 am

In good time a DC-DC charger is on the shopping list as it's a better charger than the alternator and has the benefits of the smaller fuse and voltage drop story as mentioned. At the moment the alternator will have to do the charging in the car, and a normal 220v charger outside the car.

The nice thing about the thick cables is that I terminated them in the back of the pajero with an anderson connector so even though I left the battery box at home I can still plug my compressor or something in there while the engine is running and quickly use that port without having to open the engine bay for access to the battery.
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Re: DIY : Dual battery

Tue Mar 29, 2011 11:44 am

box is done and currently running the 40" LCD TV and decoder for SWAMBO to see how long it lasts on the battery.

I also finished off the last of the drilled holes with a 650w drill running from the inverter and it was as powerful as the wall socket feed.

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PS : I know the inverter sits slightly skew - I did it on purpose to help moisture collect and roll out the bottom instead of hanging about. I don't know how big a help it is if any but worth a shot to help it last longer.
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Re: DIY : Dual battery

Tue Mar 29, 2011 12:10 pm

a little bit of use with the 650w drill and 35 minutes on a 40" LCD TV and decoder and the low voltage alarm went off.

Not bad I suppose from a tiny battery.
to
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Re: DIY : Dual battery

Wed Mar 30, 2011 10:02 am

Marius,

I managed to get one of the same from Midas (same price too). Thanks for the lead.

Thanks also for everyones contributions on wiring and set-up. I think the toolbox is a great idea!

Anton

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