Hi, I have a Isuzu bus with 3 x 130w solar panels, morning star pro 30 solar controller connected to 3  120ah AGM batteries which are about 7 years old. I know nothing about nothing about the electrical side of things but feel that the system is aging and in need of replacement. First night away batteries got down to about 20%. Only running 12v fridge and a few led lights. I am thinking that if I change to lithium this will enable me to replace the 3 batteries with 2 large lithium batterie, giving me room to install a diesel heater. I want professional advice on the selection and installation of a suitable system. Please, only opinions from those qualified. Thankyou

Hi RWC,

There are many people here who aren't 'qualified'  that will know more than many that are.  So what qualifications are you looking for because that are many on here and other forums can tell you the horror stories about the work of so called 'qualified' people.  Actually you don't need any qualifications to do 12V work but knowledge does help.

No, I'm not qualified, but I build my own LiFePO4 batteries, install my own solar panels and wire my own vehicles and likewise there are many others that do the same.  

For a start a system needs to be designed, for how you travel, where you stay, the power that you use and the means to replace it.  

Fridge is a 12v Dometic compressor RUC5208X

3 x 12v ALCO AGM 120ah Ritar RA12-120S batteries.

Sinergex puresine2 1000w inverter

Solar panels 3 x 130w kyocera

20 amp solar regulator Morningstar

Thanks Peter, wow! They would want to be pretty good batteries. Would I be better getting one large battery or several smaller ones?  You see all the battery fires on the news, not good. My current batteries are mounted under seating, inside bus, with venting. 

My solar controller is a Victron 100/20 (20 amps) MPPT.

In the manual it says a maximum of 290 watts of solar input for 12 volt setup.

In perfect conditions & square to the sun my 120 watts (6 x 20 watts) were up to 137 watts. The MPPT was outputting up to 11 amps. My previous Victron 75/10 (10 amps) MPPT would simply stop outputting at 10 amps.

While at it replacing things. Put isolation switches in for each of the 3 solar panels. It just makes it so much simpler tracking down a problem with any one of the solar panels.

One panel can bring the other 2 panels to their knees if not wired properly.

RWC wrote:

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Thanks Peter, wow! They would want to be pretty good batteries. Would I be better getting one large battery or several smaller ones?  You see all the battery fires on the news, not good. My current batteries are mounted under seating, inside bus, with venting. 

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 I would buy the batteries that suit the space you have available. 1 would be easier to wire and cheaper.

Venting needs to be external.

Those solar panels you have are oldies, but goodies. :)

 Cheers,

Peter

This is the way I would calculate your requirements:

According to the pdf manual, the fridge is rated at 9 amps on 12 volts. So if you were in a hot area where the fridge ran non stop for 24 hours (quite unlikely) it would consume over 200 amp hours (9 x 24). Actual consumption would usually be a lot less, depending on ambient temperature, installation quality and opening/closing etc. Assuming a 50% duty cycle, which would probably be reasonable for summer days and usage, that means around 100 ah. In cooler locations it would be less but you should size your system to cover high demand.

If other usage is minimal then your solar input needs to generate say 120 ah or more per day to keep up. I would plan for more as you may use a TV or laptop or make other lifestyle changes. Then allow say another 50% more at least to recover from deeper discharges (wet and cloudy days etc). That suggests at least 200 ah per day needed from solar. The more solar the better.

I think the present 3 x 130w panels are a bit small. Perhaps you could supplement them with a portable panel for use only if needed. Hobart in winter would require more than Cairns in summer even with clear skies (although fridge consumption would also be be very low). I will leave it to others to explore this further.

Then take into account those wet days or even partly cloudy days. Your battery capacity determines how long you can go before you run out of power. If your usage is 120 amps and there is very little solar input, that means draining your batteries about 100 ah per day (actuallty a bit less because cloudy and wet days usually mean less drain by the fridge). The size of your battery bank determines how long before your fridge cuts out. If your 3 x 120 ah batteries were lithium you could probably get through most weather events without running out.

Are We Lost wrote:

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According to the pdf manual, the fridge is rated at 9 amps on 12 volts. So if you were in a hot area where the fridge ran non stop for 24 hours (quite unlikely) it would consume over 200 amp hours (9 x 24). 

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 Not really.

Rated current is not consumption.

ruc5208x_9600028640_119246.pdf

What is says is that the power consumption is 75W. At a nominal 12.5V that is 6A, not 9A.

Cheers,

Peter

Yes, I agree with that calculation and perhaps the quoted 9 amps should be a bit less. But I note their specs show the same watts for each of three capacities, with different amperages. With the same 75 watts draw consumption , you would expect to see the same amperage for each. No doubt the larger fridge daily cycle run time per day would be greater for each size up.

Edit: amended as per following comment

The amps drawn by the compressor will vary with the voltage offered and the speed of the compressor. This compressor is probably a BD50 Seecop/Danfoss. The speed can be easily varied which will vary the power required to run it and the duty cycle.
www.secop.com/fileadmin/user_upload/SEPS/datasheets/en/bd50f_101z1220_r134a_12-24vdc_09-2024_desd100e702.pdf
This is not a big fridge for this compressor.
Watt hours is a more accurate measurement.

I am not sure why we are having this discussion. The OP already knows if his solar is sufficient for this fridge.

Cheers,
Peter

The best thing you can do for a fridge is insulated it as long as it doesn't have the condenser coil in the fridge walls.

Extra fridge insulation wattage test

https://thegreynomads.activeboard.com/t65059593

I have very limited space in the car for batteries, two of the three 26ah batteries shoehorned under the seat, so I did some tests on the 28L Waeco going in the car so it would use the least amount of power possible. 28L is the largest fridge I could fit without taking over.

I heated a bedroom in the house for about 3 days to 35°C with three heaters (pretty horrendous electricity consumption) & tested the fridge with different levels of insulation. I also installed a very efficient Noctua fan in the fridge from an old computer. Put a baffle around the fan as well, as the fridge design was recirculating hot air. Added velcro as hot air was traveling up between the fridge & cover reducing thermal efficiency. With foam sleeping mats added efficiency is better than 30mm of XPS foam but I didn't have accurate figures.

28 litre fridge per hour, ambient 35°C, fridge set at +2°C

0.0140 kW/h The uncovered fridge.

0.0132 kW/h Standard cover.

0.0116 kW/h 30mm XPS foam.

0.0082 kW/h 60mm XPS foam.

The 100 means the controller can cope with higher voltage input. The Victron 100/20 can have 4  12v panels in series. The Victron 75/10 can have 3 panels in series.

The Victron 100/20 can output 12v 24v & 48v, all voltages at 20 amps maximum.

The maximum amps output is the second figure. If you run a 24 volt system (handy if the inverter has 24v input) you double the output wattage of the controller (if you have enough solar), but same amps. Then run lights & TV etc via a 24 to 12v DC-DC converter.

For ease of wiring most of us have a 12 volt system. You could run a 24 volt system & use a 24 to 12v DC to DC converter. That's the output side of things for the controller.

A seperate DC-DC issue. If you are charging the caravan batteries while driving. It's worth installing a DC-DC charger between the car & caravan batteries, as near the caravan batteries as reasonably possible. This keeps the voltage up which is lost in resistance from the long run from the front of the car.

The advantage of running 2 panels in series is that first thing in the morning when the panels don't get much sun, the voltage will be higher & get the controller fired up sooner.

The disadvantage is that a small shadow can bring those 2 panels to their knees.

The advantage of running your 3 panels in parallel (with 3 panels you don't have a choice) is that if 1 panel has a small shadow the other 2 panels will keep working, as long as there are diodes between the panels. But obviously you only have single panel voltage of about 17 volts so the controller won't fire up as early in the morning.

Because I have 6 small panels I can run 2 in series which gives about 35 volts, x those in 3 sets parallel. So I get the best of both worlds.

All my gear, controllers, dc-dc & chargers are Victron. It's not that much more expensive & I just don't want to be in a remote area with some second rate product. Also having multiple items. I can still use my old 75/10 controller. I have redundancy.

If you are always in parts of Australia without the sun being more or less overhead. You can use a smaller controller as there will be less input & thus output.

If you are further north & the controller is not large enough, it will be running at capacity. If it's really hot ambient temperature the controller will throttle back to protect itself. Good ventilation is required for it. The controller will not work as well & it may even switch off entirely until it cools down.

The Victron Bluetooth ones are great. Or you can set up a larger systems with Bluetooth. So you can get a really good idea what is going on. After awhile you probably won't use it other than to track down problems if they occur. Like I said to be able to switch off each of the solar panels individually to solve problems is handy. Safer than crawling around on the roof cutting & reconnecting wires 

If you want to quickly work out how many watts your 390 watts of panels are producing, assuming everything is in perfect working order. Let's say the sun is 30° above the horizon, the panels are horizontal on the caravan roof, good heavy wiring (one would have calculated wire resistance for the run & x 2 for both positive & negative), with zero shadows including self shadowing from other things on the caravan roof & the solar panels are spotlessly clean.

Type in your smartphone calculator, select the scientific mode so you can select 'sin'

Type 390 then press 'sin' button, then bracket '( )' button once, then angle of sun above horizon let's say 30.

So the phone screen will look like this: 390sin(30 = 195

So 195 watts of solar output.

So you can work out quickly how little solar input you are getting early in the morning &/or winter etc.

The MPPT controllers constantly adjust the voltage output to suit the battery's level of charge. Firstly to charge at the best voltage. Then to get the maximum amps. So if the battery has been used it will need a lower voltage charge. So then the controller will output more amps. 

This is part of the reason I am getting so many amps out of a tiny solar setup. If the controller is not large enough those extra amps can't be used because the controller is at its output limit. 

If further north in summer you will have more solar, so it's not so critical the size of the controller other than the fact that you are overloading the controller which obviously has its own issues. 

If ambient temperature is high you will need more amps for the fridge as it's going to have to work harder. Then you want to make sure use are getting the benefit of all the amps from the solar panels by having a large enough controller.

RWC wrote:

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Fridge is a 12v Dometic compressor RUC5208X

3 x 12v ALCO AGM 120ah Ritar RA12-120S batteries.

Sinergex puresine2 1000w inverter

Solar panels 3 x 130w kyocera

20 amp solar regulator Morningstar

 

-- Edited by RWC on Sunday 22nd of June 2025 11:11:41 AM

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 Hi RWC,

Ok so what else are you running besides the fridge, lights...how many, TV?, CPAP? What do u run off the inverter and what is the wattage?  All the little things can add up so we need to calculate your approximate power draw.  Then we need to look at a system to replace that power.

What type of camping do you do and how long free camping.  Some people only spend a couple of nights and it is easy to design a system, others like myself spend longer and we have to account for inclement weather.  Camping under trees can also cause power generating issues.  Is your alternator connected to your house batteries?

At the end of the day it is all about designing a system that fulfills your needs, you cant just copy off someone else because we all camp differently, travel differently and use different power hungry appliances.

More than happy to help out.

And forget about the battery fires on the news because those batteries are a different chemistry to LiFePO4 but too many people use the general term lithium and wouldn't know about the different chemistries.  

Tim  

Thanks for responding. I have purchased 3 of the same batteries as were originally fitted. We intend only free camping for a maximum of a week or so with most stays in caravan parks. I do have a Honda 2kw generator and a 150 solar panel to top up if needed. Main usage is the fridge with various led lights to be used as required. No A/C or welding. A couple of sirrocco fan. Will also have a small tv/dvd player to watch movie. The obligatory mobile chargers too. The 3 solar panels are in parallel with diodes between them.  We do have a small 240v fan heater for use when 240v available in caravan parks in winter.  Anything else required? Also bought this monitor, see photo below. 

I was waiting for your response but only had until yesterday to get the deal. Previous batteries had lasted 10 years. 

Hi RWC,

My apologies by at times I get caught up in other things.

I wasn't sure if this was a system that was working for you before or whether when you stated 'our first night away' it was the first time you had used it. If it was working for you before then you should have no issues especially with a generator as back up other side of the shunt.  With the Victron shunt you will be able to monitor your exact power usage and get a good feeling of how the system is coping.

The shunt has to be wired into the negative side of the battery and all loads have to be connected to the other side (load side) of the shunt. The battery negative connection of your Morningstar solar controller and the solar negative have to be connected to the load side of the shunt.  Depending on how your van is wired the van loads may run from a direct connection from your battery or from the load terminals of your Morningstar.  They are the two terminals on the right and usually depicted by a light bulb.

If the existing is a direct battery connection then again the negative has to be run to the other side of the shunt. If the van loads are run through the Morningstar, then the negative cable supplying the loads has to run to the other side of the shunt and from there to the Morningstar negative load terminal.  Hope that makes sense. With the latter form of connection the Morningstar is programmed to act as a low voltage disconnect for the van's 12V loads.

Similarly the negative of your inverter has to run to the load side of the shunt and then from the negative side of the shunt to your battery negative with the appropriate cable size.

Good luck

Tim