Dual battery system for Discovery 1
Before my trip to Morocco I wanted to ensure that I had a spare battery charged and ready to go just in case I had issues with my main battery. However, when I was looking at the off the shelf systems available they came in at about £84 ish for a system without long HD cables or about £70 for one without a display. I also came across some system which looked thrown together for about £55.
So, I thought it would be a good idea to do one myself. I'm not an auto electrician, but I know enough about electronics to easily work out the parts needed and I bought on line the minimum parts I needed to create my own system, these were;
- 180amp heavy duty relay £12
- Connectors etc £5
- 2xvolt LED meters £6
So with the total of £23 (not including the spare battery, or cabling which you will need) I started fitting the components to my Land Rover. I do have a fair collection of tools and things like shrink tubing, cable soldering iron etc so I did not include these in the costs.
Firstly the positioning where the second battery will go is actually quite easy on a Discovery 1. There is already a space for a second battery in the engine bay in front of the air box. If you have a snorkel as i do all you need to do is remove the jack and pop it into the boot and you have a ready made compartment.
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| 2nd battery location Discovery 1 |
So that's the easy bit, the next bit it to understand how to wire the 2nd battery up, there are a few options here;
- Just run a live from the 1st batter to the 2nd, not recommended at all, but I have seen it done. The problem with this setup is you need the same batteries and they are not isolated from each other so if one goes wrong and loses charge the other one will leaving you with no power.
- Install a relay which switched charge to the 2nd battery when the voltage on the alternator is enough to charge both batteries, does not suffer from the issues with option 1, and does isolate the batteries.
- Dual alternators one for each battery
I opted for point 2 its not the cheapest works and is reliable. Option 3 would be fab but at £100 for a new alternator + brackets and cabling it really would be a luxury.
No with option 2 you need to do some wiring. I found this diagram on the net which lays out what you need to do.
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| Dual battery wiring diagram |
You can see from the diagram it has two batteries, a relay to split the charge, fuses at the + posts for the batteries to connect to each other, a feed from an existing source to trigger the relay, which again is fused and also a meter to test the charge system.
Now I have included some pictures below on how I wired the system up. I used to do a lot of electronic, but not on cars, and I was always amazed just how bad some of the wiring on some other systems was done. So I have tried to ensure if you have not done this before I have given some tips on how to prevent things going wrong. It is at this point where my cabling will probably break due to smart arse karma, but hey ho.
Wiring the main cables
To put the crimp terminals onto the thick cables you will need to get a good crimp tool, I have a Laser 5284 crimp tool and some battery terminal connectors. The crimp tool works by inserting the wire you want to crimp with a crimp on the end and smacking it with a hammer to crate the crimp, the tool is about £15 but it worth all its money it creates very good crimp connections.
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| Laser 5284 crimp tool |
The crimp terminal end connectors you need look like this.
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| Crimp terminals |
You should get some shrink tubing as well to ensure you cover the end of any cables you are making up, this will prevent any short in the system.
You will need to lay out the cable where you want to run it in your engine bay, cut it to length and then put the terminal connectors on and complete the main cabling. Some images below.
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| Cable run around the back of the engine in P-Clips |
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| Cable run along the lines of existing cable |
When you have crimped and connected the cables the ends should look like this.
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| Crimped and shrink wrapped connectors |
In the image above you will see a smaller cable with a crimp connector on it, like the little crimp connectors you get from halfords etc. These are a nightmare, in my opinion they are ok to do wiring with if you don't have to 100% rely on them, but they tent to break and causing shorts or a loss of circuit.. So what I would suggest you do with these is the following.
Firstly strip your wire you are going to connect to a crimp.
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| Stripped wire, sorry its blurry |
Then tin the wire with some solder, put the end connector on and then solder them together. This will give you a strong wet joint between the crimp and the wire, then put some shrink tube over it.
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| Crimped and soldered |
This will give you a really good connection for you smaller wires which should not fail. Tip, when you do your soldeing put the shrink tubing on 1st, its unlilely it will fit over the connectors after.
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| Crimped, soldered and shrink wrapped connection wire |
Now all you have to do assuming you have done all your cables right is to connect the system up.
This is the connection from the + terminal on the 2nd battery to the 1st fuse box.
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| In line 60amp fuse holder |
The cables is run around the car to the relay.
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| Cable run |
All the way around to the relay, you can see the connectors setup on it below.
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| Dual battery relay wired |
The red small cable is the one that goes to the back of the alternator, on my land rover there is a wire which supplies a voltage to make the dashboard low battery light go out, I know I'm sure it has a better more technica name for it. You basically run the red wire from the relay to a 1amp fuse holder, then around the engine following the wiring to the alternator and clip the relay feed wire to the back of the alternator using a quick splice crimp connector to link the relay to this wire, see below.
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| Quick splice connector |
This is where mine is on the alternator.
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| Alternator connection |
The thick red cable from the relay then goes to the main battery via a 2nd 60 amp fues to the + on the battery.
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| Relay to behind the battery box |
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| Up onto the + terminal |
The other small black cable from on the relay goes to earth on the chassis or bodywork.
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| Relay to earth. |
Also the 2nd battery needs and earth and good one, I have run the - on the 2nd battery to the chassis leg.
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| 2nd battery earth to chassis leg |
Make sure you cable tidy everything up and nothing is moving around, screw the relay to somewhere sensible, mine is on the inner wing, and give it all a tug to ensure its not going to come loose.
Testing the Dual Battery setup
To test the system you will need a multimeter, you can see my 2nd battery standard voltage below is 13.13v standing.
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| 2nd battery not being charged |
When the engine is on and running this goes upto the charging voltage of the alternator, see below, mine is 14.18v, probably should be a little higher.
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| 2nd battery on charge |
If you do not get this when the system is on you have a wiring fault, you will need to use your fused multimeter to check the following.
- You feed from the alternator is working, set the multimeter to Volts put the + into the fuse holder from your feed wire into the fuse holder, then fuse holder to + to multimeter, - on multimeter to - on earth or battery. With the engine off this should ready 0v, with the engine on it should be 12v+. If you get the 12v bit this is not where the issues is, reconnect the fuse and relay. If there is an issue I'll bet it with the connector you put on the back of the alternator
- Check your small earth wire from the relay to ground, disconnect it from the relay, keep it connected to the car and do a voltage check from the + on the primary battery to the - wire to earth, this should read something like 12v+, if this is not reading then your ground is not good enough and you may need to find another, or run it to - on the primary battery
- Then check each connection from the + on the primary battery, with the connector off the battery, to after the 1st fuse, set the multimeter to ohm you should get 0 resistance, if you do not and you get a high reading -1 on mine then there is no circuit and the fuse has gone or is not connected, if the fuse has blow you have done something wrong with the wiring, check it all again do not just replace the fuse
- Check the continuity of the cable from the relay around the engine bay to the other side of the 2nd fuse before it connects to the battery, it you get a high reading, -1 on my multimeter there is a fault in the connections or fuse here. I had a fuse issue here it did not connect properly, so I had to un-bolt it and put it back
- Now lastly a continuity check from the second battery to the fuse
Please remember a car battery can kill you or cause a fire so if you are uncomfortable with electronics get someone else to do the system.
Anyway, assuming you have cables it right and I take no responsibility for what you do at all, you will have a working 2nd battery. I have done mine as an overland backup battery and feed for my CB radio.
I will fit the dual voltage meters into the system at a later date.
Good luck and have fun.
