12V DC fridge flattens batteries

Willdoe · Member

12V DC fridge flattens batteries

Cupie · Guru

I wired mine up so that I have the option of running the fridge from the tug while driving and the solar is charging the batteries.

I can change this to charge the batteries while driving.

I never run the 3way off the van batteries.

Delta18 · Guru

As Cupie said, never run a 3 way directly off your van battery & expect the car to charge that battery.

Run your van wire from the Andersen Plug to the fridge and it will run happily.

You will need a separate charging system for the van battery, ideally a DC-DC charger powered from the car and/or solar.

Mamil · Senior Member

Delta18 wrote:
As Cupie said, never run a 3 way directly off your van battery & expect the car to charge that battery.

Just wondering why you say that? I have my 3-way fridge connected to the van battery when I'm towing. The Anderson feed from the car goes through a Redarc BMS30 to charge the battery and run the fridge while underway. Am I doing something wrong?

Cupie · Guru

Mamil wrote:
Delta18 wrote:
As Cupie said, never run a 3 way directly off your van battery & expect the car to charge that battery.
Just wondering why you say that? I have my 3-way fridge connected to the van battery when I'm towing. The Anderson feed from the car goes through a Redarc BMS30 to charge the battery and run the fridge while underway. Am I doing something wrong?

If it works then its OK. What you are doing may well be the most common approach.

I just chose to do it differently & perhaps more cheaply. (I don't use a Redarc BMS30 .. or even a VSR ... just an old fashioned relay off the accessory feed on the GQ Patrol to deliver power to the van. The Van's DC DC charger uses the solar to charge the battery while I have the anderson plug feed direct to the Fridge. If I wish, I can connect the anderson plug feed to the van battery via the van's DC DC charger which in my case disconnects the solar.

swamp · Senior Member

HI
Solution is simple
Straight altenaror charging avg outpit 14.2 volts
NOT BIG ENOUGH CABLES
9mtrs of 13mmsq //6b&s 18amps at .4 volt drop
9mtrs of 25mmsq //3 b&s 35 amps at .4 volt drop

Currently the amp load is pulling the voltage down to far.
!3.8 volts is the minimum to charge a battery

EG Your charging batteries at 3 amps once the fridge is operating and that's if your using 13mmsq cable . Your cable is smaller .

Solution
Either run 2 x 13mmsq cables from vehicle 1 x charge and 1 x fridge supply
or
Run 1x 25mmsq cable

Use a RV fridge switch in 12v wiring --turns fridge on only if moving
Install a dc/dc charger at van batt. WARNING only connect 3 way to the vehicle side of charger

Mamil · Senior Member

Cupie wrote:
Mamil wrote:
Delta18 wrote:
As Cupie said, never run a 3 way directly off your van battery & expect the car to charge that battery.
Just wondering why you say that? I have my 3-way fridge connected to the van battery when I'm towing. The Anderson feed from the car goes through a Redarc BMS30 to charge the battery and run the fridge while underway. Am I doing something wrong?
If it works then its OK. What you are doing may well be the most common approach.
I just chose to do it differently & perhaps more cheaply. (I don't use a Redarc BMS30 .. or even a VSR ... just an old fashioned relay off the accessory feed on the GQ Patrol to deliver power to the van. The Van's DC DC charger uses the solar to charge the battery while I have the anderson plug feed direct to the Fridge. If I wish, I can connect the anderson plug feed to the van battery via the van's DC DC charger which in my case disconnects the solar.

Thanks Cupie. Yes the Redarc BMS is a substantial investment, but I needed a new charger anyway when I switched to Lithium batteries, and I like the way the Redarc can juggle two inputs at the same time, so my solar on the roof is used as priority to run the fridge and charge the battery while underway, and it tops up from the car as necessary. As it incorporates a DC/DC converter I also know I'm getting the right voltage for my battery at all times. By everything going through the BMS it does mean I'm limited to 30Amps total, so with 15A going to the fridge I have a maximum battery charge of 15A, but that hasn't been a limitation yet, but we'll see if that starts to be an issue as I do more freedom camping.

Mamil · Senior Member

swamp wrote:

Install a dc/dc charger at van batt. WARNING only connect 3 way to the vehicle side of charger

Hi Swamp, as above reply to Cupie, I have a DC/DC charger and I have attached the fridge and battery to the van side of it, not the vehicle side. As the charger has two inputs, solar and the Anderson from the car, while I'm underway once the battery is charged I can pretty much run the fridge off just the solar. I do have an ignition switched relay so that the fridge doesn't run the van battery down when I stop the vehicle. You've now got me worried that I'm doing something wrong, so perhaps you could explain a bit more the down side to connecting the fridge to the van side of the charger? Thanks.

Cupie · Guru

Mamil wrote:
Cupie wrote:
Mamil wrote:
Delta18 wrote:
As Cupie said, never run a 3 way directly off your van battery & expect the car to charge that battery.
Just wondering why you say that? I have my 3-way fridge connected to the van battery when I'm towing. The Anderson feed from the car goes through a Redarc BMS30 to charge the battery and run the fridge while underway. Am I doing something wrong?
If it works then its OK. What you are doing may well be the most common approach.
I just chose to do it differently & perhaps more cheaply. (I don't use a Redarc BMS30 .. or even a VSR ... just an old fashioned relay off the accessory feed on the GQ Patrol to deliver power to the van. The Van's DC DC charger uses the solar to charge the battery while I have the anderson plug feed direct to the Fridge. If I wish, I can connect the anderson plug feed to the van battery via the van's DC DC charger which in my case disconnects the solar.
Thanks Cupie. Yes the Redarc BMS is a substantial investment, but I needed a new charger anyway when I switched to Lithium batteries, and I like the way the Redarc can juggle two inputs at the same time, so my solar on the roof is used as priority to run the fridge and charge the battery while underway, and it tops up from the car as necessary. As it incorporates a DC/DC converter I also know I'm getting the right voltage for my battery at all times. By everything going through the BMS it does mean I'm limited to 30Amps total, so with 15A going to the fridge I have a maximum battery charge of 15A, but that hasn't been a limitation yet, but we'll see if that starts to be an issue as I do more freedom camping.

Sounds like your set up is way way ahead of my cheapie DIY set up. As I rarely go off grid I couldn't justify the big spend of a Redarc based set up.

My SIL has a great camper trailer battery set up based on a fantastic Redarc unit with all the bells & whistles. I'm very envious.

My DC DC charger can handle only one input & always gives preference to the Vehicle/Alternator source which is a PITA. If that weren't the case I would have probably wired it to eliminate the need to manually change the anderson plug connections between 'run fridge' or 'charge battery' when driving.

Mamil · Senior Member

Cupie wrote:
Mamil wrote:
Cupie wrote:
Mamil wrote:
Delta18 wrote:
As Cupie said, never run a 3 way directly off your van battery & expect the car to charge that battery.
Just wondering why you say that? I have my 3-way fridge connected to the van battery when I'm towing. The Anderson feed from the car goes through a Redarc BMS30 to charge the battery and run the fridge while underway. Am I doing something wrong?
If it works then its OK. What you are doing may well be the most common approach.
I just chose to do it differently & perhaps more cheaply. (I don't use a Redarc BMS30 .. or even a VSR ... just an old fashioned relay off the accessory feed on the GQ Patrol to deliver power to the van. The Van's DC DC charger uses the solar to charge the battery while I have the anderson plug feed direct to the Fridge. If I wish, I can connect the anderson plug feed to the van battery via the van's DC DC charger which in my case disconnects the solar.
Thanks Cupie. Yes the Redarc BMS is a substantial investment, but I needed a new charger anyway when I switched to Lithium batteries, and I like the way the Redarc can juggle two inputs at the same time, so my solar on the roof is used as priority to run the fridge and charge the battery while underway, and it tops up from the car as necessary. As it incorporates a DC/DC converter I also know I'm getting the right voltage for my battery at all times. By everything going through the BMS it does mean I'm limited to 30Amps total, so with 15A going to the fridge I have a maximum battery charge of 15A, but that hasn't been a limitation yet, but we'll see if that starts to be an issue as I do more freedom camping.
Sounds like your set up is way way ahead of my cheapie DIY set up. As I rarely go off grid I couldn't justify the big spend of a Redarc based set up.
My SIL has a great camper trailer battery set up based on a fantastic Redarc unit with all the bells & whistles. I'm very envious.
My DC DC charger can handle only one input & always gives preference to the Vehicle/Alternator source which is a PITA. If that weren't the case I would have probably wired it to eliminate the need to manually change the anderson plug connections between 'run fridge' or 'charge battery' when driving.

Ha - if I was honest I couldn't justify the amount of money I spent upgrading the electrical system on my van either. I did try justifying the price of the Lithium battery to the wife once - and after a long monologue about the savings in weight, number of cycles, and depth of discharge, I got shot down in flames with one simple question - so how much was it compared to the perfectly good AGM battery we already had? So now I just accept it was one of those projects that kept me amused for many months in the design and implementation and I can't really justify it on a cost basis! I would recommend the Redarc unit though. Yes it's expensive, (but less so if you buy off Ebay rather than direct from the Redarc website) but it really is the heart of the van's electrical system. It combines an AC charger, DC/DC converter, solar MPPT controller, battery isolator, and remote SOC monitor, in one very well built unit. And just as important, especially to those often travelling, their after sales and technical support is excellent. I had an issue with mine and the Redarc regional manager turned up at my house with a replacement unit and helped me swap them over. In this age of throw away electronics and throw away customer service, how many companies still offer that kind of support?

-- Edited by Mamil on Saturday 15th of September 2018 02:02:06 PM

Brenda and Alan · Guru

Willdoe Delta18 has given you the answer you require although your post seems to have been hijacked. Connecting 3 way fridges to van batteries is a no no unless you have very substantial cabling from car battery to caravan battery AND return to the car battery. If not voltage drop along the cables will ensure the fridge draws its power mainly from the van battery. hence the flat batteries.

Alan

-- Edited by Brenda and Alan on Sunday 16th of September 2018 08:40:02 AM

swamp · Senior Member

hi
Running 12 volt 3 way fridge draws plenty of amps say around 15amps.or more .
Running a 3way on 12 volt is for ONLY while driving.
A battery charger to go from absorbtion to float ,,essentially almost switch off . It must go below 7% in amps of batt AH or for most charger3-5 amps . This is the current trigger point for switching .The voltage also lowers from 14.2down to 13.6 v THE CHARGER MUST SEE THIS Happen. This advice came from Ritar engineering boss . Mainly prevent charger from putting out especially when battery does not need it . It will/can get hot and cause a fire . This occurs a lot in boats apparently .

cable to feed dc/dc
Use 25mmsq 3b&s carries 35 amps .4 volt drop over 9mtrs
If running 3way run this off the input //car side of charger thru fuse thru RV movement switch[fridge switch] onto fridge
The dc/dc charger then connects to battery without heavy loads interfering with charging van batt.

Mamil · Senior Member

as swamp wrote:
hi
Running 12 volt 3 way fridge draws plenty of amps say around 15amps.or more .
Running a 3way on 12 volt is for ONLY while driving.
A battery charger to go from absorbtion to float ,,essentially almost switch off . It must go below 7% in amps of batt AH or for most charger3-5 amps . This is the current trigger point for switching .The voltage also lowers from 14.2down to 13.6 v THE CHARGER MUST SEE THIS Happen. This advice came from Ritar engineering boss . Mainly prevent charger from putting out especially when battery does not need it . It will/can get hot and cause a fire . This occurs a lot in boats apparently .

Hi Swamp, thanks for explaining that, I see where you are coming from now. In fact I had the same concern that the high amp draw of the fridge would prevent the battery charger going into float and thus cook the battery. I asked Redarc tech support and they reassured me that as the BMS has a shunt on the battery, it can detect the falling amps to the battery as it approaches full charge no matter what is going on with the fridge, and adjusts voltage to float accordingly. However, I agree your concern is a valid one in a system without a shunt. Anyway, I'll duck out of this one now as I've been accused of hijacking the thread and that was never my intention. Other forums I'm on welcome people to add to the thread as long as it's relevant to the original question, but I guess all forums are different and as it's only the second thread I've contributed to here I'm still learning the etiquette.

-- Edited by Mamil on Saturday 15th of September 2018 10:47:57 PM

-- Edited by Mamil on Saturday 15th of September 2018 10:48:45 PM

Kebbin · Guru

It's too easy to start a new topic rather then hijack another members post, it's also quite confusing to members trying to help. A common courtesy I would think.

Willdoe · Member

Thanks for info I will connect to anderson side of smart charger. I suspect I will have to live with the wiring the manufacturer wired the van with looks like 4 or 5 mm automotive not the 10 I initially quoted.

T1 Terry · Guru

Lash out and spend a whole $179 on one of these www.jaycar.com.au/12-24v-30a-dc-to-dc-battery-charger/p/MB3689 and you will arrive with a charged house battery and a cold fridge. Just make sure there isn't a linked cable in the back of the fridge that joins the car supply to the house battery because that will create a loop that ends up with rather hot cables and connections after a few hundred kms. I suspect this is the problem that is flattening your house batteries at the moment, there is not enough current available through the car wiring without the voltage dropping, so the fridge is really being powered by the house batteries. Connect the DC to DC to the car cables and then to the house battery. Cut the car battery connections from behind the fridge and fit a BP connector over the ends to avoid short circuits. This way the DC to DC charger will boost the voltage coming from the car supply and charge the house battery, 15amps for the fridge and 15 amps towards recharging the battery. Combine that with the solar charging and you should make the evening camp with charged batteries and everything in the fridge still nice and cold

T1 Terry

oldtrack123 · Guru

Brenda and Alan wrote:
Willdoe Delta18 has given you the answer you require although your post seems to have been hijacked. Connecting 3 way fridges to van batteries is a no no unless you have very substantial cabling from car battery to caravan battery AND return to the car battery. If not voltage drop along the cables will ensure the fridge draws its power mainly from the van battery. hence the flat batteries.
Alan

-- Edited by Brenda and Alan on Sunday 16th of September 2018 08:40:02 AM

A big ditto to above

Absorption fridges should not be connected to the van battery, no matter what the van battery charging source!

Absorption fridges are best when supplied directly by their own heavy cables [min 6B&S] from the vehicle alternator.

Depending on the fridge model, an isolating relay may be required so the fridge is only powered by 12V when the vehicle alternator is outputting

With adequate wiring, & correct wiring method, you should not need a DC/Dc charger!!!

It is also unwise to run an absorption fridge off the output side of a dc/dc charger, especially if the feed cables to the DC/Dc charger are undersized

-- Edited by oldtrack123 on Tuesday 18th of September 2018 03:37:47 PM

Cupie · Guru

oldtrack123 wrote:
Brenda and Alan wrote:
Willdoe Delta18 has given you the answer you require although your post seems to have been hijacked. Connecting 3 way fridges to van batteries is a no no unless you have very substantial cabling from car battery to caravan battery AND return to the car battery. If not voltage drop along the cables will ensure the fridge draws its power mainly from the van battery. hence the flat batteries.
Alan

-- Edited by Brenda and Alan on Sunday 16th of September 2018 08:40:02 AM
A big ditto to above
Absorption fridges should not be connected to the van battery, no matter what the van battery charging source!
Absorption fridges are best when supplied directly by their own heavy cables from the vehicle alternator.
Depending on the fridge model, an isolating relay may be required so the fridge is only powered by 12V when the vehicle alternator is outputting

Well bugger me, looks like I fluked it. As per my first post (before I hijacked the post .. poo hoo), that is what I did. But I have the ability to change my set up (by switching anderson plug connections) & just charge the van battery if I choose (pity about the fridge though, if I choose that option).