Additional solar system & B2B for compressor fridge

wfdTamar

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Hi. I've had a 2002 Hymer Classic B584 for a season and fitted solar to it. I'm fairly competent mechanically and technically, but the finer points of electrics are not something I do often enough to warrant learning it.

My Hymer has an EBL 99 (capable of 10 Amps solar & 16 Amps alternator charging I think). I installed 200 watts of solar through a Votronic Duo Digital 250 (with temp lead & LCD display), but direct from Votronic to the Yuasa EFB-36 100Ah leisure battery (LB). I did this rather than connect it via the EBL because the solar limit of the EBL is 10 amps. The spec's of the 2 panels combined showed just over 11 amps max (but as it is I could have done it as they didn't get near that). Anyway it all seems to have worked fine, though the 12 volts on my 3 way fridge did finally die, but I think that was just coincidence. 4 months of a long hot summer were too much for it.

I had the AES control from the Votronic solar controller connected to the fridge. This signals the fridge to run off the LB when there is excess solar power. It would only ever run like that for a few minutes - maybe 5 mins max (drawing 10 amps). I do wonder if bypassing the EBL could have caused trouble? Could that have over powered the fridge control panel? But surely that's no different to when you're driving and it's running off the alternator, or would the fridge have better voltage control coming via the EBL? The Votronic's max solar charge voltage is 14.4. If that went through to the fridge could that have cooked the control panel?

The fridge is not economic to fix mostly because the suspected faulty part (the main control panel & front panel - Dometic RM6405) is unavailable. Yes, I (and a motorhome repair bloke) have looked into all possibilities, but it's a no go. Besides that, it was pretty rubbish last summer in 25-37 degrees. The space is under bench and has an upper and lower vent to outside.

Right, so I'm looking at about £1000 for supply and fit of a new 3 way. That (and better fridge performance) got me thinking of a compressor fridge - either 12 volt, or 240 volt via inverter, with an extra solar system to drive it.

My thinking is rather than enlarge the current solar system, which runs all the usual leisure stuff, I'd install a separate system just to run the fridge. A couple of reasons - to save replacing stuff which is installed and working, and a bigger system would most likely be beyond the capacity of the existing EBL/vehicle charging system.

I'm thinking:
200 watts fixed solar (possibly 100-200 portable as well for inclement weather)
Votronic Duo Digital 430 solar controller (with LCD display and temp lead)
Votronic 30A B2B charger (with LCD display near driver seat)
Yuasa EFB-36 100Ah battery (possibly two)

Victron mains charger 30A 3 outlet (already have this)

12 volt compressor -
Isotherm Freeline 115 Elegance £799

A really nice spec, low amp fridge. The freezer only goes down to -8, but that's enough for my use.
267 watts per 24 hour @ 25 degrees = 22.25 ah per day

Total cost including fridge and 2 batteries/200 watts solar £1830!


or

a standard domestic 240 volt fridge that'll fit in the space, run via Victron Phoenix inverter as I already have a 500VA one, but may get a 250VA one, if that'd run it. These can run in 'eco mode' using less standby power. The eco mode might work for a fridge. Or there's a technique to wire an inverter up to the fridge thermometer so there is no standby draw (need to look into that).

£105 A++ Not sure of the power usage. They state 0.36 kWh per day @ 240 volts I can't work out the equivalent in DC.

You can remove the top which may gain enough to fit it in. What I'm not sure about with a domestic fridge is do they use the sides/top to expel heat or would the existing vents in my Hymer (at top & bottom rear of fridge space) be ok to cool it (possibly with extra fans)? All the installation instructions for house fridges require space all round but that's assuming being installed in an unvented space/room. If you just ventilate the rear, where the compressor is, to the outside, is that ok?

Older style fridges have a cooling 'radiator' panel on the back, but more modern ones seem to only have a small opening around the compressor.

Total for 240 volt fridge including fridge and 2 batteries/200 watts solar about £1200. A lot less than 12 volt. Even to allow for inverter losses so bigger solar that is a big difference.

I'd also thought of putting a switch like this in between fridge and batteries (the new setup and the existing leisure one) so I could pick which solar setup (battery) supplied the fridge. Just in case I ran the fridge solar too low, but still had reserve in the standard LB.

 
Last edited:

jagmanx

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1,791
I am no Motorhome electrician..I am sure others will help but..

My thoughts are
1 Yes another solar panel
2 Yes another leisure battery
BUT feed all the solar into the LB bank of 2 or even 3 batteries which will then supply all your needs.
In addition when you are travelling the LB Bank will be charged off the alternator.

No advantage in having two systems
One may get low when you have loads in the other.

No doubt others will have more knowledge of the details of the various components etc
 

wfdTamar

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108
Can't do that because it would overload the EBL. The existing electronics in this motorhome aren't meant for big loads like a compressor fridge. Even with the solar system I have now I use all the capacity I have occasionally (drop the battery to 50% charge).

I'd need more than one extra panel. That's one reason to have a second system. The B2B is there to charge the second system off the alternator when driving. I had thought putting the switch in between fridge and all leisure batteries would enable using all capacity off either system.
 

eurajohn

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137
Just a thought but do you have sufficient available payload to accommodate that lot?
 

wfdTamar

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108
Payload - yes definitely a consideration when talking 2 panels (15kg), possibly 2 batteries (50kg). All up could be 100kg. Pretty sure I'd be ok now travelling alone, but I need to plan for a future possible sale too. No point trying to sell it if payload is low. Vehicle allowable total weight now is 3400kg. Mind you, I haven't weighed it empty with all the existing clobber I've added.
 

eurajohn

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137
Don't know what others might think but you could possibly get a shock.
Are you back in Tasmania or still in France?
 

wfdTamar

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108
Tassie since early September.

Shock from how much it would cost? I presume you mean the 240 stuff, but that's only from inverter to fridge.
 

wfdTamar

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108
I did intend to early on, but it seemed fine and even when I fitted air helper spring things on the back (more for stability than weight assist) I only had them pumped to 0.5-1 bar. Any higher than that it was like a pogo stick at the back.
 

eurajohn

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137
Thought I remembered you'd made a few improvements, it is surprising how the odd little add ons increase your weight.
A lot of people (me included) have been caught out thinking they were OK only to find differently when put on a weighbridge.
 

SquirrellCook

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250
Domestic Fridges are harder to run than you might think. This 200watts of solar and a 100ah battery will work in ideal conditions. From experience you really need to double that. I've just increased to 600watts of solar for those dull days we sometimes get.
 

wfdTamar

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108
Yes, quite a few additions to the basic Hymer I bought, but nothing heavy other than the solar, but yes it all adds up. Of course, if I'd been sensible, I would have weighed it before adding anything and kept track of additions so know where I am.

I'd have at least 200 watts and a 100Ah battery, but possibly add a portable panel to be able to point it best at the sun and a second battery. All that dedicated to the fridge as I already have the 200 watt/100Ah leisure setup for the rest of the van stuff. I only use it during the warmer half of the year from about May to Sept.
 

yorkslass

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Get in touch with VW allan, i'm pretty sure he has a domestic fridge, but in a heavier van.
 

wfdTamar

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Just reading wildebus's thread here - using almost the same fridge and the exact model inverter I have, so very useful.

 

wildebus

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Just reading wildebus's thread here - using almost the same fridge and the exact model inverter I have, so very useful.

As I have mentioned in that thread you linked to, the 240V fridge has worked faultlessly for over two years now.

Just a comment on something you mused over earlier "...may get a 250VA one, if that'd run it. ". Answer there will be no. The fridge may just use 35W or so when running, but the inrush power to start the compressor means an inverter capacity way above what the fridge normally wants is needed. the 500VA unit you have already is the smallest you could get away with.

Ref Solar and Batteries for Fridge ... You will know best how your current setup works in terms of how much capacity is left at the end of the day and how much the solar harvests on a typical day, but I would have thought if you are using it in the warmer (sunnier?) time of the year (May to Sept in Tasmania? wouldn't that be Winter? I'm guessing this a motorhome based in Europe?) the harvesting from a 100W panel would not be far off what you need to run that fridge and keep the battery topped ready for overnight?
I used to go to VW Festivals in my VW T5 with 12V compressor fridge and 200W Solar and would leave the events on Sunday with full batteries and the solar from around 2PM or earlier would be doing nothing as batteries full already.
An extra 100Ah battery would be a good idea and in fact if you join the two batteries together ('properly', not just using an isolator switch), you will get a better overall performance then having two separate systems. When it comes to battery banks, when done right, 2+2 > 4.

PS. These Domestic 240V Fridges are extremely light so I can't imagine changing from a 3-way to a 240V would result in a weight increase. Extra Battery will of course, and Solar Panel will, but they are light as well.

Finally, that fridge you linked to ... It is similar to mine and is the same brand, but two key differences ... 1) it has a larger and better freezer section (I have just an 'ice box' in mine) but 2) you pay for that in power consumption. The specs quote 131kW/Annum. My fridge is 80kW/Annum. That is a BIG difference. On my testing, I found their quoted 80kW/Annum (220W/Day) to be very accurate, so I would expect that 131kW (360W/Day) to be accurate also. That makes the 98L unit have a power consumption figure of over 50% more!
 

wfdTamar

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108
Yes, really useful stuff - only on page 6 so far and it's 10 pm here. My Hymer is in the UK. I use it over there (well, preferably France).

I'm thinking worst case when sizing things - maybe 4 days of rubbish solar/rain and not much driving. Though I was surprised how little light still produces some charge in the panels. Though that's when I tend to watch a lot of TV (28" 240 volt or on my MacBook Air). That's when I was using most of the system I currently have.

I'm now wondering about redoing my existing solar and leisure battery setup to save cost and complexity. Maybe a single system of 300 watts fixed panels, 100 portable, 2 x 100Ah batteries, but still with a B2B charger so the EBL won't be overloaded (unless the B2B would cause the EBL problems).

Ah right. I hadn't picked up on that fridge difference. Still just looking at fridge options. I think one consideration was overall height and the 98 is a tad lower than the 93 with a removable top. Don't want a big freezer, so probably go for the one you got or similar (if they fit). Hard to beat it for bang for buck though.
 

wildebus

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The 'ice box' in mine works well. The instructions say basically that it won't freeze things, but it will keep frozen things frozen, and I use it mainly for ice cubes, ice lollies, that kind of thing. I will physically measure my fridge and post the results here (sometimes quoted measurements include packing, so you never know, it may fit!)
I would not hestiate to either recommend that make or buy again (and I did buy another one last month as it was on a 'too good to miss' deal even though I have no current use for it - but now if the fitted one goes wrong, I can swap it for a brand new one for less than a little service on a 3-way jobby!)
 

wfdTamar

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108
I reckon the only thing I'd want the freezer to do is keep ice cream in an edible state - from supermarket, to freezer, to gob. Actually one of the drawbacks of the Freeline 12 volt fridge in my OP is that the freezer is too big (for my needs). They have another model which has a smaller one if I decide to go 12 volt. However the choice is really between 3 way and 240 volt. 12 volt is just so much more expensive (what wit the fridge and power setup as well).

I did toy with the idea of no freezer as that uses a lot less power (the Sterling test shows that). However it may hurt resale and I do like an ice cream :)

I asked Inventor the following (before I'd seen your testing in low temps):
'Hi. Mini bar fridge 98 litre. It's SN/T climate class, so that's 16-43 degrees. Is it ok below 16, say down to 8? With the plastic top off what is the exact height? I want to mount it under a bench with vents to allow air circulation at rear top and bottom.'

Typically, they answered:
Regarding your request, let us inform you that his refrigerator is designed to be used in household and similar residential areas such as:
  • Farmhouses; staff kitchen areas in shops, offices and other working environments;
  • By clients in hotels, motels bed and breakfast and other residential type environments.
Moreover, it not advised to install the appliance in areas that are too humid or too cold, such as construction sites, garages or wine cellars. Do not place the unit in direct sunlight or near other heating sources like radiators, cookers, ovens or hobs and do not use the unit near heat sources, chemicals, radiators, flammable materials or fire.

This mini fridge should operate in a location where the ambient temperature corresponds to the climate classification for which it is designed. Ventilation openings, in both the appliance’s enclosure and in the built-in structure should be clear of obstructions.


I didn't want to 'fess up and say I was putting it in a motorhome because they'd just say 'no way José'. Annoyingly they didn't answer mt vital question - the height without the top. Probably because that isn't in their canned responses on the computer.
 

wfdTamar

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108
What I'm really concerned about though is how to integrate the extra solar and battery(s) into my Hymers existing system without killing the EBL.
 

Mark135

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What I'm really concerned about though is how to integrate the extra solar and battery(s) into my Hymers existing system without killing the EBL.
Can you not fit a stand alone solar controller just for the extra panel and wire it directly to the LB (fused of course) leaving the current panel and EBL alone? This would be just the same as connecting a portable panel with it's own controller. I don't believe multiple charger conflict with each other.
 

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