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-   -   Using Inverter with dual battery system (http://www.horizonsunlimited.com/hubb/other-4wd-overland-tech/using-inverter-dual-battery-system-61606)

Vleis 30 Jan 2012 21:03

Using Inverter with dual battery system
Hi all

From the posts it looks like a 300 to 600 W "cheap inverter is fine for charging cameras, laptops etc. Anything I should know about when installing or using such a gadget with a dual battery system (one normal the other one deep cycle)? I assume it needs to be linked up to the normal one :o ?

I am a bit concerned about the amps it would draw, don’t think it should run through the cigarette lighter.


Barrie Dunbar 31 Jan 2012 07:49

Goeie more Meat,
Your inverter (and any other accessory for that matter) must be on your auxiliary(deep cycle) battery. Never put anything on your starter (cold cranking) battery, except a winch.
Lekker reis,

Vleis 31 Jan 2012 10:45

Dankie Barrie :)

Barrie Dunbar 31 Jan 2012 10:55

I should also have mentioned; it's critical to have a good earth (direct to chassis) and a decent fuse (I use 50A on a 1000W inverter)

dash 31 Jan 2012 11:43

If all you are talking about using it for is "charging cameras, laptops, etc", then why go for an inverter at all? What you're talking about is going...

12V DC -- (inverter) -> 240V AC -- (device charger) -> somewhere between 5V and 20V DC

Which is probably a good way of heating up the inside of your vehicle, but probably not of making your leisure battery last.

Why not just buy 12V chargers for the devices, and stick to a 12V power circuit in the vehicle?

Vleis 31 Jan 2012 12:17

Thanks for the feedback. I looked at getting 12v changer/s but then I need to consider which connector types I need. With the inverter I though at least I can use a single device to "trickle charge" 240V items whilst we on the move.

Peter Girling 31 Jan 2012 12:36

AC-DC? I'm curious...
Hi Vleis,

I agree with Dash; you'll waste an awful lot of energy converting 12vDC to 240vAC and then back to DC. Just look at the size of a 1000W inverter and see how much heat it kicks out.

Also, unless it's outputting good sine wave AC, you'll fritz the batteries on your laptop/camera, etc. in time.

A good quality sine wave 1000Winverter is going to cost a couple of hundred euros, then you've got to mount it in your vehicle and hard-wire it.

For less than 30 euro you can by a small DC/DC converter with selectable output 3v-20v complete with an assortment of connectors. Fits in the palm of your hand.

And then there's all sorts of stuff like MotorMonkey and PowerMonkey, etc...

Hope that helps.

Happy trails,

Peter Girling
Atlas Overland - Specialist adventure tour company providing off-road holidays for 4x4 enthusiasts in Europe and North Africa.
Tours to Morocco, Tunisia, Arctic Circle, Alps, Pyrenees, Corsica, Eastern Europe and UK weekend tours.

Griffdowg 31 Jan 2012 14:32

x3 on the above.

I spent a bit of time gather 12v supplies for our electrical items. Laptop charger was the easiest, then get a few of those USB/12v cig lighter connectors or hardwire USB connectors into the dash. you can charge a lot of things off USB.

Hunt down 12v chargers for your phone, camera, videocamera etc. Ebay is a good place to start.

This way your not wasting anything from your batteries.


Glennn1234 31 Jan 2012 14:57

Just to charge laptops and simular devices all you need is a decent 200 watt square wave inverter, battery charging does not use much wattage, and square wave will not destroy battery's as stated above.(well at least I have never seen issue with cameras and laptops ) In some cases the circuitry in the charging system will burn itself up but in my experience (retired electrician) the only devices which do not like square wave are microwaves and hand held battery devices like drill motors. And larger inverters will not be drawing larger current as stated above unless device demands it (charging will not, but if you wanted to run a AC powered drill or something like that then of course a larger unit will want to draw more that your MC fuse will allow)
You can get a decent sq wave inverter for 20 US. (smaller units are not very big ). If you only wanted to charge Ipod or any USB then just a little cig lighter usp adapter will take no space at all and a lot of cameras can be charted by USB now.

twobob 31 Jan 2012 21:03

One thing to consider with dual systems is the isolator, especially if using large inverters. Of the two types, electronic or manual, I prefer a large marine manual type (I mount in the engine bay and therefore a wet area) but my recommendation is electronic until you are disciplined in switching.
An alternative to the isolator is a battery that has four poles (two positive and two negative one dedicated to motor start) that would give you the peace of mind of never drawing too much power that you can't start your engine.

crinklystarfish 1 Feb 2012 09:46

For the jobs the OP wants than a small (250W continuous / 500W surge) quasi sine wave (ie cheap) inverter powered from a cigarette lighter socket should be fine.

There'd be very little issue in charging from the starter battery when actually driving along as the alternator should easily cope. This way the item being charged could be kept in the cab and easily to hand - might be handy for the camera.

When not driving, the same inverter should be plugged into a cig socket connected to / otherwise powered from the leisure battery only, as a laptop - especially if actually booted and used whilst it's charging - could deplete enough from the starter battery to cause starting problems.

This assumes all the electrical hardware is in good condition and there is a split charging system on board that isolates the leisure battery from the starter either automatically or manually.

AliBaba 1 Feb 2012 09:53


Originally Posted by crinklystarfish (Post 365456)
For the jobs the OP wants than a small (250W continuous / 500W surge) quasi sine wave (ie cheap) inverter powered from a cigarette lighter socket should be fine.

250W means at least 20A, I would say that's far more then most sockets (and wires) are designed for.

ralphhardwick 1 Feb 2012 12:44

We used a 300W inverter on our last trip for exactly this reason. We would only run it when the engine was on and all the spare batteries would be plugged in and charging throughout the day.

However for our next trip I have invested in a series of 12v charges for each battery type (all less that £10 from amazon or ebay). We will be charging batteries for a GoPro and Kodak playsport video cameras and 2 different olympus still cameras. In addition there will be a netbook.

In contrast to all the technical issues discussed above our main reason for changing is space and tidiness.
The normal 240/220v chargers usually come with longer leads and large plugs in addition the laptop has a transformer in the line. To have all these plugged in it required a '4 gang' extension lead running to the inverter. This meant we had to mount that somewhere and have all the leads coiled up (not good) or secured somehow.

The battery chargers are all small and of a consistent design (ABC Products Olympus Li40C Battery Charger Li40B Li42B: Amazon.co.uk: Electronics) with short leads. I will 'mount' them all together and use a simple 12v 4 way adapter (http://www.amazon.co.uk/WAY-CIGARETT...099830&sr=8-21).
The power consuption is low and this solution will take up hardly any space.
For the netbook I bought a simple 12 v adapter (Netbook Car Charger for Samsung NP-N110 NP-N120 NP-N130: Amazon.co.uk: Electronics).
I also have a 12v AA battery charger for the camera flash.

None of these items were expensive and they create a neat little vehicle installation which takes up hardly any room.

I shall plug them into an ignition fed supply so that they only draw current when we're driving that way they become 'fit and forget' until you need to swap the batteries.

I will try and add a picture once I have it fully installed.

Vleis 1 Feb 2012 16:02

Thanks all, looks like it will be 12V chargers has my vote in the end

crinklystarfish 1 Feb 2012 17:57


Originally Posted by AliBaba (Post 365459)
250W means at least 20A, I would say that's far more then most sockets (and wires) are designed for.

I see how the numbers might seem alarmist but nothing he suggested would actually pull anything like 20A (12V) - even though the inverter was capable of supplying it. The inverter will respond to demand, not just supply its maximum power all the time.

A laptop, even if drawing heavily on its processor etc would only pull a fraction of that current and wouldn't cause any issue for a standard vehicle's cig lighter / wiring, even taking into account the inefficiencies in the inverter itself. I've actually done it in several vehicles without any problem and reps up and down the country rely on the cig lighter / inverter / laptop solution. Camera's etc would draw even less.

Of course, if he were to try to plug in a travel kettle or some-such device the 'magic smoke' would quickly appear.

Hope that clears up any misconceptions.



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