Transform dual battery into 1 main and 1 accessory (1 Viewer)

[nicolas2b54]

Hello all,

I'm Nicolas from France.
I recently purchased a 2001 hdj100. My primary goal is to use it next year in a 6-month road trip in Europe (and more I hope after that).
I start to plan for some mod and be self sufficient in electricity is one of those.
After many reading and watching from forum/blog/youtube, I would like to use a dual battery system :
- 1 for the vehicle (start, radio, lights ...)
- 1 for accessory (fridge, phone, tablet ...)

The car I bought is already equipped with 2 batteries and each of got things plug on it.


What is the best things to do :
- keep it that way and plug the accessories on the battery #2 with what already exists
- free the #2 with a cable to the battery #1 from the secondary fuse box (in the picture above), and use the #2 only for the accessories.

Thank you for your ideas.

 

[nicolas2b54]

Forgot to mention : a sticker under the hood tells that the batteries are in parallel. So my main worry is that if I not modify the circuit and plug my accessories on the battery #2, it will drain the #1 (during the night, or if I stay 2 day without driving)

 

[YvesNL]

You will have to isolate one battery from the other. This way your fridge etc. won't drain your starting battery.
An easy way to do this is by taking off the positive terminal off one battery and connecting it through a Victron Cyrix relay.

This relay will close automatically when the vehicle (alternator) is charging and disconnect when your devices are draining the second battery.
If you charge one of the batteries (solar panel for example) the other will start charging (after a while) too.
It really is connect and forget about it, works flawless. I like the Victron Stuff, but you can also use other battery isolators.


Here is a picture:

There are many other different and better ways to do this. This one is simple, cheap and works great.

Keep in mind that your 1HD-FTE might need two batteries to start in very cold weather. The Cyrix relay has an input to manually close the relay and use the accessories to help start the car.

 

[nicolas2b54]

You will have to isolate one battery from the other. This way your fridge etc. won't drain your starting battery.
An easy way to do this is by taking off the positive terminal off one battery and connecting it through a Victron Cyrix relay.
There are many other different and better ways to do this. This one is simple, cheap and works great.

 

[nicolas2b54]

You will have to isolate one battery from the other. This way your fridge etc. won't drain your starting battery.
An easy way to do this is by taking off the positive terminal off one battery and connecting it through a Victron Cyrix relay.

There are many other different and better ways to do this. This one is simple, cheap and works great.

Thanks for the explanation and the brand.

What bother me is what's already on the battery #2. What do I do with those ? I have not yet identified what it's used for.
On the fuse box, I read :
- ALT-S (7.5A)
- MAIN (100A)
- ALT (140A)
- J/B NO.2 (100A)

 

[YvesNL]

The two battery terminals are linked through a cable that runs from the left to the right. So if you take the battery terminal off, like in your picture, everything will work fine on the single battery.

Then you connect the terminal you took off to the battery through a battery isolator. I made another picture:

If you connect the battery isolator you do not need the battery pole anymore. Make sure this is isolated and can't hit anything metal.
You could also cut this bit off but then you can't go back to original if you want.
You can wrap it in isolation tape & cloth tape for example or use some heat shrink. Make sure it isn't rubbing against anything because eventually it will wear through.

This is not how I did in on my HDJ100, I have a third (LiFePO4) battery in the rear that powers my accessories. The front two are used for winching and starting.
Previously I had a normal battery in the rear and used the Cyrix isolator for years without a single problem. Most of my mates use the device as well, one of them in the configuration in this & my previous post.

If you use a normal battery use the Cyrix-CT, the 120A version will be enough for what you're describing.

 

[nicolas2b54]

This is not how I did in on my HDJ100, I have a third (LiFePO4) battery in the rear that powers my accessories. The front two are used for winching and starting.
Previously I had a normal battery in the rear and used the Cyrix isolator for years without a single problem. Most of my mates use the device as well, one of them in the configuration in this & my previous post.

If you use a normal battery use the Cyrix-CT, the 120A version will be enough for what you're describing.

Hi,

Thanks for all the details. It's way more clear in my head !

The Cyrix-CT seems a very good solution. Does it works also if the accessories battery is LiFePO4 ? I read a lot about that kind and that seems able to handle full cycle, which is what we want for accessories (isn't it ?)

 

[YvesNL]

You are correct, a LiFePO4 battery is perfect for our needs.

The Cyrix-CT is not suitable for LiFePO4, but they sell another one for that, the Cyrix-Li-CT.
It also has high and low temp cutoff I believe, you'll have to check the datasheet.