Basic solar charging system

[1 Cup]

50p a watt sold.

 

[trevskoda]

Well thank you all for the advice.
I have ended up buying the ecoworthy 390 watt kit plus some sika 544 adhesive.
For £210 for the kit although it will provide a lot more power than I need I will fit it with the pwm controller that comes with it for now and see how it goes on our annual Scottish trip this year. Later on when our single battery needs replacing, if we find our power requirements have grown it will be an easy job to fit an Mppt controller and another battery.

With that amount of solar i would at least go 2 batteries of 100ah, i have 200w solar and 2 90ah truck batteries which cost me £45 each.

 

[Martin P]

Well that was my Saturdays work.
Quite pleased actually

 

[1 Cup]

Well that was my Saturdays work.
Quite pleased actually

Nice

 

[trevskoda]

Looks neat, does that control unit also charge the eng battery, is it a mppt unit.

 

[Martin P]

Nice

Thank you.
Fisherman's recommendation of Sika 544 was bang on. Taped around brackets, scuffed with some 120 grit and a wipe with celly thinners. Happy with bond

Looks neat, does that control unit also charge the eng battery, is it a mppt unit.

Thanks. The engine battery will charge through the motorhome calira unit when hab battery voltage hits certain point, ( I forget what that is). It's a PWM unit, It came as a deal with the panels, I will change it to a Victron unit later but have run out of spare money for now.

 

[Martin P]

Now I'm wondering if the spare load terminals on the controller could run the 12v element of the fridge

 

[wildebus]

Now I'm wondering if the spare load terminals on the controller could run the 12v element of the fridge

nope.
if it is a 3-way, you would need to run the 12V off the starter battery and if a compressor, the surge will knock out the load output when the compressor kicks in.

 

[trevskoda]

Surly the fridge can be wired direct to the les battery rather than the starter one, a switch could be used when the gas is of.

 

[1 Cup]

Them sc can power lights and charge old phones . But what you use you lose. Put all solar power into battery untill full, then use for alternative stuff.

Learn as you go. batteries first.

 

[Martin P]

Interesting. It's a 3 way fridge. I was just wondering, if I had some spare power from the panels, could that be used to take some of the gas usage off the fridge. For the cost of some wire and a couple of relays.
I would think that Mr Wildebus is right but it is fun to hypothesise

 

[merl]

Interesting. It's a 3 way fridge. I was just wondering, if I had some spare power from the panels, could that be used to take some of the gas usage off the fridge. For the cost of some wire and a couple of relays.
I would think that Mr Wildebus is right but it is fun to hypothesise

I've considered what you're thinking myself actually and I think it would work in a fashion.
If 3 way fridges have thermostatic control over the gas flame which I'm pretty sure they do then adding some additional cooling power via the 12v element would surely lead to the gas thermostat turning down sooner than it would have done on gas only, therefore a savings on gas. You'd need some pretty basic logic system switching the 12v side in and out, not sure if the parameters that are selectable for the 'load'' output of the SC would doable because of the very low slope of a lithium discharge curve and the relatively wide difference between on charge and off charge voltage.

 

[Martin P]

I was thinking of running a pair of wires from the extra "load" terminals of the sc down to the fridge and using an arduino to control a couple of relays. I think it should be possible to set up so if power is sensed from the alternator/starter battery that feed is switched in , if no power detected the solar is switched in and the solar could be switched off if the current drops below a definable amount.
Devils in the details

 

[merl]

I was thinking of running a pair of wires from the extra "load" terminals of the sc down to the fridge and using an arduino to control a couple of relays. I think it should be possible to set up so if power is sensed from the alternator/starter battery that feed is switched in , if no power detected the solar is switched in and the solar could be switched off if the current drops below a definable amount.
Devils in the details

In my head I'd only want the fridge to get a boost from the SC when I'd got power to spare, ie the lithium was full but there was still power to be had from the panels. OR the batteries were saying 80% or more AND full sun was expected for the foreseeable. Unless I'm using some kind of hive based algorithm (if it's even possible?) I'd have to switch the 'boost' in manually but at some point I'd inevitably I'll forget to turn it off and regret ever trying to be a smart arse in the first place!!
Applying 12v at the same time as gas may be too much because I don't think the gas ever modulates 'Off' and the fridge could get too cold? you'd probably have to apply a reduced voltage say 9V or switch 12v on and off at short intervals.
An interesting possibility though

 

[wildebus]

In my head I'd only want the fridge to get a boost from the SC when I'd got power to spare, ie the lithium was full but there was still power to be had from the panels. OR the batteries were saying 80% or more AND full sun was expected for the foreseeable. Unless I'm using some kind of hive based algorithm (if it's even possible?)

The LOAD output on the Victron Solar Controllers are programmable and can be set to turn on and off depending on various parameters, including voltage level. Because A Lithium Battery effectively gets its full charge during the bulk - Continuous Current - phase where the voltage builds up as the battery gets closer to fully charged, you could actually set it so the LOAD turns on when the voltage hits say 14.3V (I stop charging my Lithiums at 14.19V for example).
So in that aspect it is possible, but you would need a fridge with a reliable AES so it switches power inputs as need be. And then you have the problem of when you are driving you don't want to be running on the gas but the 12V, and how do you ensure the LOAD is active whenever driving.
You could add a relay that swaps the 12V input between Starter Battery supply and LOAD supply depending on the D+ state but going down a path of complications for an answer with minimal benefit.
FWIW, I use 'Excess Solar' (which I don't see very often in reality) to heat the water via the electric element. That is a far more useful option (IMO)

I'd have to switch the 'boost' in manually but at some point I'd inevitably I'll forget to turn it off and regret ever trying to be a smart arse in the first place!!
Applying 12v at the same time as gas may be too much because I don't think the gas ever modulates 'Off' and the fridge could get too cold? you'd probably have to apply a reduced voltage say 9V or switch 12v on and off at short intervals.
An interesting possibility though

I guess with a basic fridge you could bypass the fridge control and have any or all of the power sources active on a fridge and add a thermostat inside that will connect and disconnect them as the fridge needs cooling, but I would think the type of fridge that you could do that to would likely be one that needs a manual gas ignition so that would not be any good then!

 

[merl]

t I would think the type of fridge that you could do that to would likely be one that needs a manual gas ignition so that would not be any good then!

Yeh, I've contemplated modding my manual 3way to make it automatic but igniting the gas is the big stumbling block!
Going back to adding some 12v to assist a gas fridge, Id expect a situation where the battery was essentially full but there was an overcast sky with the SC able to only supply a couple of amps. The relay would kick in but the fridge load would cause the battery volts to drop and the relay would cut out immediately, the 3 amps of solar would bring the voltage back up instantly and the relay would clock back in and the process repeats and you get an annoying relay chatter. Wonder if the cut in and cut out voltages could be set so as to prevent chatter without depleting the batteries too low? Guess that depends on how fine the parameters can be set. My SC is 100mv increments, looks like the Victron is just 10mV?

 

[wildebus]

Yeh, I've contemplated modding my manual 3way to make it automatic but igniting the gas is the big stumbling block!
Going back to adding some 12v to assist a gas fridge, Id expect a situation where the battery was essentially full but there was an overcast sky with the SC able to only supply a couple of amps. The relay would kick in but the fridge load would cause the battery volts to drop and the relay would cut out immediately, the 3 amps of solar would bring the voltage back up instantly and the relay would clock back in and the process repeats and you get an annoying relay chatter. Wonder if the cut in and cut out voltages could be set so as to prevent chatter without depleting the batteries too low? Guess that depends on how fine the parameters can be set.

My SC is 100mv increments, looks like the Victron is just 10mV?

not something I have looked at TBH. I set my LOAD output to "always on" as it provides my Habitation power ( I do this so I can log the Power Use and also if I want turn off all the hab power remotely via VRM).

 

[Martin P]

The 12 element in my fridge is 195 watts which is about 16 amps. Quite a big load

 

[wildebus]

The 12 element in my fridge is 195 watts which is about 16 amps. Quite a big load

Yup. Absorption fridges are extremely inefficient on electricity. If the objective is to use spare harvested power to save gas when camping off-grid, using it to heat the water is a far better idea, both in terms of efficient use and also simplicity - as if you have an electric heater element it is just a matter of activating power to it.

 

[Martin P]

Yup. Absorption fridges are extremely inefficient on electricity. If the objective is to use spare harvested power to save gas when camping off-grid, using it to heat the water is a far better idea, both in terms of efficient use and also simplicity - as if you have an electric heater element it is just a matter of activating power to it.

Through an inverter?