Relays to switch solar power

[noelex]

Thanks for the comments Lemain
To overcome the problem with the thermostat controling the evaporator not the box temp an alternative is to get the solar regulator to turn the fridge off completetly at night as well as bypassing the thermostat when excess power was available. (they can be programed to do lots of clever things)
This would give a very energy effecent fridge but with more temperature variation.
The solar regulator can also dump excess power into other devices such as fuel polishing or laptop charging.

 

[whipper_snapper]

[ QUOTE ]
The solar regulator can also dump excess power into other devices such as fuel polishing or laptop charging.

[/ QUOTE ]

Or fans!


When the sun is shining and all the other important kit like fridges are happy, using any additional waste power for fans to stir the air up a bit makes sense.

 

[Anonymous]

We use so much power for the watermaker, telly, two laptops, pumps, etc., that the fridge is of no real concern to us. We have 2 off 185W solar panels and a 6.5kVA diesel generator (which we run as little as possible) and an 80A Mastervolt charger feeding domestic batteries of 560Ah. Works fine for us at anchor all summer in the Med. Different lifestyles or transats might make a difference (I have no Ocean experience) though I guess you don't want your food to be suffering wide temperature swings on a transat?

 

[tri39]

I must say I like the idea of the solar panels switching cabin fans on when the fridge is cold enough!! However we are very KISS, just turning the fridge on at breakfast and off at dusk. During the day it's always on since I binned the corroded thermostat. Works fine for us, and we don't have a separate starter battery either. Altho we do have a VSR to transfer spare charge to the windlass/radio battery.
However I have now ordered a Fridgemate! But hang on, I might need a solar regulator then, but I find constant use of fridge and autopilot and fans and radio, plus windlass, use all the power we are producing.

 

[tri39]

Fridgemate has arrived. Stays on for 12 mins when first connecting and then afterwards will disconnnect if batt voltage drops below 11.5volts.
This should prevent cycling off and on repeatedly.

 

[Anonymous]

[ QUOTE ]
Fridgemate has arrived. Stays on for 12 mins when first connecting and then afterwards will disconnnect if batt voltage drops below 11.5volts.
This should prevent cycling off and on repeatedly.

[/ QUOTE ]Is that all it does? /forums/images/graemlins/confused.gif

 

[whipper_snapper]

[ QUOTE ]
11.5volts.

[/ QUOTE ]

/forums/images/graemlins/confused.gif

 

[tri39]

Yes, and I think the fridge won't run below that voltage anyway!!

Wot's in that 'orrible paper cup, whippersnapper?

 

[whipper_snapper]

There is something wrong there. 11.5V is waaay too low. It should be switching at over 13V


ARe you sure you haven't pressed the manual override button ?!


mushy peas

 

[tri39]

It switches OFF at 11.5v, no info on what voltage it switches back on.
I won't try it till May.

 

[andyjohnson]

Dear David,

There are several thresholds built into Fridge Mate including auto detection of 12V or 24V battery system. Once charging is detected it switches power through to the fridge and allows 12 minutes operation before continually monitoring the battery voltage. This allows for the instant drop in battery voltage during the start-up of the fridge compressor and lets things settle down. The 12 minutes is a good compromise as it is long enough to get the fridge plate cold but not take any significant energy out of the batteries if charging did not continue and it also worked very well in solar panel and wind generator system tests.

This link is to the "Wind and Sun" section of our website, hope it helps. http://www.jwmarine.co.uk/fridge_mate_windsun.html.

In manual mode, different thresholds come into play as Fridge Mate then looks for a low battery voltage condition and again account is taken of voltage drop during compressor start-up.

Yours,

Andy Johnson
JWMarine

 

[tri39]

Thnx Andy, at what voltage does the Fridgemate switch back on when it detect charging from any source. The link doesn't work for me.

 

[Anonymous]

From the wiring diagrams Fridgemate has no extra temperature detection device? All it does is to turn the main power on and off, just like a breaker?

That's what I am doing with a Maplin kit thermostat...same wiring schematic as yours. I turn the evaporator temperature knob to minimum (-25C, I imagine, as I can achieve 18C in the cabinet) and then control on the Maplin (I have modified the design a tad to change the hysteresis but it is otherwise constructed to kit). But my thermostat is aimed at keeping the fridge temperature exactly right regardless of the electrical situation -- entirely different objectives.

Looking a the Fridgemate, if the fridge evaporator stat is set to, say, -5C to give a cabinet temperature of around +5C then even if the engine is running for 24 hours, the fridge will still cycle to keep the evaporator at around -5C. I can't see what good it is doing in that situation. When the engine is off and the battery starts to show lower volts then the Fridgemate cuts the fridge off. So the cabinet temp will rise. But due to the way the fridge is controlled by evaporator and not cabinet temperature, when the engine is started the fridge will still cycle to keep the evaporator at -5C i.e. it will not be hard-on. Or am I missing something?

There are systems, such as engine-powered freezers, that are very powerful and pull down holding plates when the engine is running, but the Fridgemate doesn't seem to do that?

 

[Anonymous]

You need to remove the trailing full stop after html

 

[lenseman]

You could try any one of these Voltage Controlled Relays from Radio Spares.

Their maximum current is 5 Amps but might be OK for your requirements?