Position of Aux. Battery

oiddad · Veteran Member

Position of Aux. Battery

Radar · Guru

That surprises me, our 2014 Navara charges the second battery in the tub though an isolator when the motor is going. Alternator is pumping at a good rate of charge.

In ours the second battery in the tub runs the 12 volt portable frig and though a Anderson plug, supports the 340watts of solar to the caravan's 110amp house battery with heavy cable. This also gives us 220 amps of usable power via that cable and if things get that bad that the batties get low, we can start the car and recharge the batteries.

We are very light power uses, short time of tv, led lighting, my test showed about 18amps max between 6pm and 9pm.

When on the move we normally don't switch the frig onto 12 volt after being on power or gas overnight, we run the frig at morning coffee break and lunch on gas and only sometimes do we ever run the big frig on 12 volt in the afternoon while travelling, there is exceptions, western sun beating down on the frig side of the caravan while travelling. We also only move about 4 hours a day and the frig generally will hold its temperture in those periods. The ice cream stays frozen.

A couple of months back, March, April in NSW, we did regularuly run the frig on 12 volt all day while we were driving as I was experimenting to see how the electrics would hold up. September last year after down sizing the battery system to save weight from the caravan going from 205amps to 110amps, saving of 36kgs. The test was very successful with 14 weeks of touring.

I just remembered while changing the battery set up to the one battery, I rewired the frig and it now draws direct from the caravan house battery, now with less then 2.5 metres of heavy cabling instead of the 8 metres of heavy cable needed to be supplied from the front of the car

My Anderson plug now helps the 340watts of solar feed the caravan battery.

Our system is very simple and to the point cheap as. Bonus it works.

Hope this edit makes more sense.

-- Edited by Radar on Saturday 19th of June 2021 08:07:24 AM

oiddad · Veteran Member

Thanks for the reply. So how exactly is yours wired up? I admit I'm a little confused on how yours now works?

oiddad · Veteran Member

Sorry .... you said "changing the battery I rewired the frig and it draws from the caravan frig now" ..... do you mean the van fridge is now powered by the van battery?

Mamil · Senior Member

Is it a 3-way fridge in the van? If so this could be pulling about 16A, plus compressor fridge in tub 5A, plus charging aux battery another 10A or so. Sounds like you are trying to run too much off your 25A DC/DC charger. If you want to continue to run both fridges off the aux battery (advantage being they are both running even when the engine isn't on) then I suggest upgrade all wiring to at least 16mm2 and upgrade to the Redarc BCDC 1240. Or you could go back to having the van fridge run direct off the alternator and give it a dedicated DC/DC charger to overcome the volt drop and smart alternator issues you were having before. Disadvantage of the latter solution is that the van fridge will only run when the car is running, but maybe you can switch it over to gas at other times if it is indeed a 3-way.

Radar · Guru

Radar wrote:
That surprises me your Narava is not keeping the charge up, our 2014 D40 Spanish built Navara charges the second battery in the tub though an isolator when the motor is going. Alternator is pumping at a good rate of charge.
In ours the second battery in the tub runs the 12 volt portable frig and though a Anderson plug, supports the 340watts of solar to the caravan's 110amp house battery with heavy cable. This also gives us 220 amps of usable power via that cable and if things get that bad that the batteries get low, we can start the car and recharge the batteries.
We are very light 12volt power uses, short time of tv only, led lighting, my test showed about 18amps max between 6pm and 9pm of a night.
When on the move we normally don't switch the 23amp draw frig onto 12 volt after being on power or gas overnight, we run the frig at morning coffee break and lunch on gas and only sometimes do we ever run the big frig on 12 volt in the afternoon while travelling, there is exceptions, western sun beating down on the frig side of the caravan while travelling. We also only move about 4 hours a day and the frig generally will hold its temperture in those periods. The ice cream stays frozen.
A couple of months back, March, April in NSW, we did regularuly run the frig on 12 volt all day while we were driving as I was experimenting to see how the electrics would hold up. September last year after down sizing the battery system to save weight from the caravan going from 205amps to 110amps, saving of 36kgs. The test was very successful with 14 weeks of touring.
I just remembered while changing the battery set up to the one battery, I rewired the frig and it now draws direct from the caravan house battery, now with less then 2.5 metres of heavy cabling instead of the 8 metres of heavy cable needed to be supplied from the front of the car
My Anderson plug now helps the 340watts of solar feed the caravan battery.
Our system is very simple and to the point cheap as. Bonus it works.

I have edited my writing hoping this makes more sence.

oiddad · Veteran Member

Thanks Radar. Do you know What type/brand of isolator you are using?

oiddad · Veteran Member

Cheers Mamil. It is a 3 way in the van and according to the sticker inside door draws a whopping 18amps. Thetford 181litre.

Mamil · Senior Member

oiddad wrote:
Cheers Mamil. It is a 3 way in the van and according to the sticker inside door draws a whopping 18amps. Thetford 181litre.

That's the root of your problem then. 3-way fridges are very power hungry on DC and really only should be used as such when hooked up to an alternator, and also via a DC/DC charger if it's a smart alternator. I had a large Dometic 180L similar to yours and I did have it running off the aux battery, but I wired it so that it was the only load on it and only ran when that battery was being charged from my alternator via a DC/DC charger. I also upgraded the wiring from the alternator to DC/DC charger to 16mm2, and from there to fridge to 10mm2 because the volt drop at 16Amps was terrible so that the fridge wasn't cooling properly anyway on DC.

Radar · Guru

oiddad wrote:
Thanks Radar. Do you know What type/brand of isolator you are using?

Yes, a red one.

oiddad · Veteran Member

Radar ... Thanks.... Great help.

oiddad · Veteran Member

Mamil thanks for that. I too have it running off the aux battery, the van fridge was wired so that it was the only load on it and only ran when that battery was being charged from my alternator via a DC/DC charger. Even then there was not much left in reserve in the battery by the end of a 4hr drive.

oiddad · Veteran Member

Radar wrote:
oiddad wrote:
Thanks Radar. Do you know What type/brand of isolator you are using?
Yes, a red one.

Wouldn't happen to know brand or more detail? Cheers.

Radar · Guru

oiddad wrote:
Radar wrote:
oiddad wrote:
Thanks Radar. Do you know What type/brand of isolator you are using?
Yes, a red one.
Wouldn't happen to know brand or more detail? Cheers.

Redarc sb112 12volt 100amp smart start, it is now going on 11 year old. There maybe better on the market now.

oiddad · Veteran Member

Thank you.

Mamil · Senior Member

oiddad wrote:
Mamil thanks for that. I too have it running off the aux battery, the van fridge was wired so that it was the only load on it and only ran when that battery was being charged from my alternator via a DC/DC charger. Even then there was not much left in reserve in the battery by the end of a 4hr drive.

Maybe the battery is just getting to the end of it's life? If it was me, I'd get in there with a DC clamp meter and check voltage and current at all points in the system to narrow down where the problem is.

oiddad · Veteran Member

Cheers. Thanks for the help.

oiddad · Veteran Member

So ....should the heavy cable to power the van fridge run from the main battery through a relay switch and through the alternator does this cable need to also go via the aux battery and redarc dcdc charger in the cab of the ute before ending at the grey anderson at the towbar which is the power connection for the van fridge? I'm pretty sure the previous owner had the cable running from main battery through relay and alternator straight to the grey anderson and not through redarc and aux battery. Hope thus makes sense

-- Edited by oiddad on Sunday 20th of June 2021 03:53:05 PM

Whenarewethere · Guru

Mamil wrote:
I suggest upgrade all wiring to at least 16mm2

At 18amps that is 0.68 volts lost over 24 metres ( both + & - ) or with 21.1mm² (4awg) is 0.35 voltage drop. You also really need to charge the battery as well, so let's say 30amps so 33.6mm² (2awg) is 0.37 voltage drop.

oiddad · Veteran Member

At the moment I'm pretty sure it's 6b&s which is around 13.5mm2? I would have thought this was enough? Pretty expensive exercise to replace it all.

Whenarewethere · Guru

It will hurt more when wifey is not happy with food going off!

Whenarewethere · Guru

There are online resistance calculators to get it right before you buy the wrong wire.

Failing that just use the above numbers. If the length is 20% more, add 20% to the voltage drop.

If there is also a 20% larger load add 20% to the voltage drop as well. Easy!

Not to forget the wiring in the actual fridge is probably a bit under size. My Waeco fridge with 55cm of wiring, so 1.1m in total + & - had a voltage drop of 0.17 volts. So I increased the cross sectional area by 2.5, so now only a 0.07 voltage drop.

No point throwing away energy in undersized wiring.

Whenarewethere · Guru

Whenarewethere wrote:
Mamil wrote:
I suggest upgrade all wiring to at least 16mm2
At 18amps that is 0.68 volts lost over 24 metres ( both + & - ) or with 21.1mm² (4awg) is 0.35 voltage drop. You also really need to charge the battery as well, so let's say 30amps so 33.6mm² (2awg) is 0.37 voltage drop.

A bit of a stuff up above.

So 18amps 24metres:

13.3mm² (6awg) 0.57 voltage drop.

16mm² 0.47 voltage drop. Not 0.68

So 13.3mm² loss & the loss of the wiring within the fridge & resistance in every connection, let's say about 0.8 volts loss.

The 4awg & 2awg figures were ok.

Mamil · Senior Member

oiddad wrote:
At the moment I'm pretty sure it's 6b&s which is around 13.5mm2? I would have thought this was enough? Pretty expensive exercise to replace it all.

That's why I'd recommend getting the meter out and measuring the actual volt drop, as other things will affect it other than wire size - there is volt drop across relays, and any connections, more if they are slightly corroded or loose. If you're getting a good 13V at the back of the fridge then no need to upgrade any wiring, but if you're not you need to find out where those pesky volts are going...

-- Edited by Mamil on Sunday 20th of June 2021 07:34:40 PM

Radar · Guru

oiddad wrote:
So ....should the heavy cable to power the van fridge run from the main battery through a relay switch and through the alternator does this cable need to also go via the aux battery and redarc dcdc charger in the cab of the ute before ending at the grey anderson at the towbar which is the power connection for the van fridge? I'm pretty sure the previous owner had the cable running from main battery through relay and alternator straight to the grey anderson and not through redarc and aux battery. Hope thus makes sense

-- Edited by oiddad on Sunday 20th of June 2021 03:53:05 PM

It all makes sense to me but it to messy, to me the trick is to keep simple.

Just remember I am a Broken Down Old Retired Truckdriver with no qualifications.

The first thing you need to be sure of is your alternator working in your favour. A trip to a Auto Electric will check it and fix it so it is working in your favour.

When I brought our Navara I sent it off to our regular service person to have them fit some extras CB radio, driving lights, electric brake controller and the Redarc isolator along with a Anderson plug on the rear bumper. I think the Auto Elec may have possibly fixed my alternator while at it.

6 months later I brought a deep cycle battery for the ute tub, this is where the fun starts, I started to add and change things progressively to where I have it today and I am very happy.

In the engine bay near our starting battery we have the Redarc connected to the starting battery, power cables run to the 110amp deep cycle battery charging that up in the tub where I run the 12volt Engel frig, then there is additional cables from the deep cycle battery that run down to the Anderson plug on the bumper bar for suppling power to the caravan deep cycle battery as back up to the 340wattts of solar we have on the roof of the caravan.

When we are parked and solar is pumping amps into the system it is also feeding in reverse to the utes tub battery via that Anderson plug. Magic.

Now the large 3 way frig which draws 23amps is powered by the caravan 110amp deep cycle battery via a short 2.5metre cable while travelling.

I have used inline fuses to protect the system. that 23amp draw just heats up most blade fuses so be careful there, buy the best parts you can, I found from auto elect the best bet. the garbage the local super spares sell will bite you when you are ill prepared.

The expensive dcdc thingy set the ute up and if you need it, then add it.

There is people on here who would pull my system to pieces but for 5 years now it has worked with small changes including dropping a second battery out of the caravan.

Hope in someway this is of help.

oiddad · Veteran Member

Mamil wrote:
oiddad wrote:
At the moment I'm pretty sure it's 6b&s which is around 13.5mm2? I would have thought this was enough? Pretty expensive exercise to replace it all.
That's why I'd recommend getting the meter out and measuring the actual volt drop, as other things will affect it other than wire size - there is volt drop across relays, and any connections, more if they are slightly corroded or loose. If you're getting a good 13V at the back of the fridge then no need to upgrade any wiring, but if you're not you need to find out where those pesky volts are going...

-- Edited by Mamil on Sunday 20th of June 2021 07:34:40 PM

Thank you very much for your time. With the engine running I am getting 13.2 at the back of the fridge, 13.25 at the grey anderson at the back of the car so all good there? Pretty sure I have tried running too much from the one aux battery and dcdc charger without replenishing what was taken out. I will get the battery properly checked. If it needs replacing I don't want to be facing the same problem during our next trip. I'll have a chat with the auto electrician and redarc advisors.

oiddad · Veteran Member

Radar thank you so much for your time and response. When you said ..."the engine bay near our starting battery we have the Redarc connected to the starting battery".... does redarc here refer to redarc isolater? The original wiring was from main battery through a Baintech isolator straight to the grey anderson but voltage drop did not allow the fridge to run. I'm wondering if redarc isolator along with running cable through the dcdc charger near the aux battery may over come this problem.

Whenarewethere · Guru

oiddad wrote:
Mamil wrote:
oiddad wrote:
At the moment I'm pretty sure it's 6b&s which is around 13.5mm2? I would have thought this was enough? Pretty expensive exercise to replace it all.
That's why I'd recommend getting the meter out and measuring the actual volt drop, as other things will affect it other than wire size - there is volt drop across relays, and any connections, more if they are slightly corroded or loose. If you're getting a good 13V at the back of the fridge then no need to upgrade any wiring, but if you're not you need to find out where those pesky volts are going...
Thank you very much for your time. With the engine running I am getting 13.2 at the back of the fridge, 13.25 at the grey anderson at the back of the car so all good there? Pretty sure I have tried running too much from the one aux battery and dcdc charger without replenishing what was taken out. I will get the battery properly checked. If it needs replacing I don't want to be facing the same problem during our next trip. I'll have a chat with the auto electrician and redarc advisors.

How many amps are you getting out of the charger?

Mamil · Senior Member

oiddad wrote:
Mamil wrote:
oiddad wrote:
At the moment I'm pretty sure it's 6b&s which is around 13.5mm2? I would have thought this was enough? Pretty expensive exercise to replace it all.
That's why I'd recommend getting the meter out and measuring the actual volt drop, as other things will affect it other than wire size - there is volt drop across relays, and any connections, more if they are slightly corroded or loose. If you're getting a good 13V at the back of the fridge then no need to upgrade any wiring, but if you're not you need to find out where those pesky volts are going...

-- Edited by Mamil on Sunday 20th of June 2021 07:34:40 PM
Thank you very much for your time. With the engine running I am getting 13.2 at the back of the fridge, 13.25 at the grey anderson at the back of the car so all good there? Pretty sure I have tried running too much from the one aux battery and dcdc charger without replenishing what was taken out. I will get the battery properly checked. If it needs replacing I don't want to be facing the same problem during our next trip. I'll have a chat with the auto electrician and redarc advisors.

Sounds like a good plan.

Radar · Guru

oiddad wrote:
Radar thank you so much for your time and response. When you said ..."the engine bay near our starting battery we have the Redarc connected to the starting battery".... does redarc here refer to redarc isolater? The original wiring was from main battery through a Baintech isolator straight to the grey anderson but voltage drop did not allow the fridge to run. I'm wondering if redarc isolator along with running cable through the dcdc charger near the aux battery may over come this problem.

yes, the Redarc isolaler is connect to the starting battery.

Baintech is gennerally good gear from my readings.

How old is the caravan you are towing.

My reason for that question is, our 2012/2013 caravan had wiring for the frig to the Anderson plug but at about 4 years old it started to play up, I discovered the earth copper wire was all blackened causing us bad earthing. The wire was inported from China and had aluminium and copper mixture, that in DC use don't work, the wire oxidises.

When I was doing my checking in 2016 why the Redarc isolator was cutting in and out, I had 13.2 volts to the frig but on turning the frig on, I only had 10.2 volts even now with everything improved it still only has about 12 volts with the frig running drawing 23amps.

Talking with the Dometic 11 metres of cable to run the frig on 12volt from the front of the car to the frig though all the electrical fittings probably need cable about 20mm thick and thats when I decided to go from the caravan house battery to the frig a run of less then 2.5 metres.

I did get some help from friends one a industrial electrician and the other a Tafe auto electrical teacher.

Have fun.