Relays to switch solar power

[mpo]

My Prostar controller gives an option of taking power direct from the solar panels once the batteries are at full charge. I am looking to run the fridge direct from this output but would like to put a low voltage detector relay in the circuit so the power is automatically switched back to battery input as the solar input drops off at the end of the day. Has anybody found a suitable device that can reliably do this. There appear to be some switches from Tyco that do exactly this but not in the 12v range.

many thanks

 

[whipper_snapper]

If you use a device like this:

http://www.jwmarine.co.uk/

you don't need to use that output to get what you want. The Fridge Mate runs the fridge when power is available - ie the battery is charged and charging- and turns it off when not. I think that achieves what you want in a simpler way.

It is what I do.

 

[mpo]

Thanks for that whipper_snapper. My solar regulator pretty much does that. It only directs power to the auxillary output if the batteries are fully charged. I understood it would be more efficient if I ran the fridge direct from the panels for as much of the day as possible before switching back to battery input. A fellow sailor has pointed me towards an Austrailian Company called Arrid that market a small Auxillary voltage regulator thru www.12volt.com.au that might do the job.

 

[whipper_snapper]

[ QUOTE ]
I understood it would be more efficient if I ran the fridge direct from the panels for as much of the day as possible before switching back to battery input.

[/ QUOTE ]

That is effectively what the fridge mate does without the need to switch between two supplies.

 

[colvic]

Is the output of the panels enough to cope with the current demand when the fridge starts up?

 

[mpo]

I am using 4 x 90w panels which have a maximum output of close to 20A which should be more than capable of coping with the fridge start up. Although I would want a relay that provides some kind of buffer to stop it chattering between switching.

 

[whipper_snapper]

But what you are proposing amounts to a more complex way of doing exactly what the fridge mate does! Pulling fridge amps from your battery only when they are at full charge with charge happening IS taking 'spare' power, just down the same wire!

 

[halcyon]

What he wants is a change-over relay that will change from regulator output to battery if the solar panel voltage drops.

This is not a problem, what could be is the regulator output before the battery is fully charged. If this changes from battery to solar panel okay, if not then you need double switching, which more envolved.

When does the regulator drop out direct supply from solar panel ?

More detail of regulator is needed.

Brian

 

[whipper_snapper]

I know what he wants - i think. I don't understand why a voltage sensitive switch like the fridge mate, set to detect charged and charging state, doesn't achieve exactly the same thing with a lot less effort.

 

[tri39]

At what voltage does the FridgeMate switch off the fridge?
And won't this mean that the fridge is just constantly turning itself off and on, due to the start up current pulling down the battery voltage?

 

[whipper_snapper]

[ QUOTE ]
At what voltage does the FridgeMate switch off the fridge?

[/ QUOTE ]

Don't know exactly. Seems to be > 13.0v ish, but not seriously looked.
It certainly does seem to behave as I want.

[ QUOTE ]
And won't this mean that the fridge is just constantly turning itself off and on, due to the start up current pulling down the battery voltage?

[/ QUOTE ]

You might think so, but it doesn't. It must have a delay to allow for the initial drop as the compressor fires up. Presumably if you had a very small battery capacity it might cycle slowly, but only when you were charging anyway.

Essentially the same circuitry in the solar reg is making the same sort of decisions when dumping power.

 

[halcyon]

The regulator switches the a output circuit to feed the fridge from solar power direct when the battery is fully charged, from original thread.

Again from original thread , it is required to switch the fridge from direct solar power to battery power if solar power is lost.

This requires a change-over relay, as the fridge needs suppling from two sources. Does the Fridge Mate have change-over contacts ?

It is not just power up when voltage is high, it is coupled to the regulator output. So the first problem is how does the regulator output control work, is it just a on / off supply, or does it switch from battery to solar, how / why does it drop out.

The actual problem, I think, is not to complicated, when the regulator output kicks in switch fridge from battery to solar power, if sun goes in revert back to battery. If regulator reverts back to charge, revert to suppling fridge from battery. Just needs a modified power supply module.

But you still need the regulator operation to say so.

Brian

 

[whipper_snapper]

mm ok. I am not trying to persuade anyone to do anything. I understand what he is trying to do, it simply makes no sense to me!

He is just taking the same power from 2 different sources instead of 1. There is a metaphor involving water tanks, overflows and supplies somewhere!

He also still needs to avoid flattening his battery when he switches to battery power. Another requirement taken care of with a single V sensitive switch on the main power supply.

 

[halcyon]

Not disagreeing with you, just expanding on the thread that you can do what the chap wants.

What we need is more detail, such as why he is so keen to switch over from battery to solar, what regulator it is.

I do understand volt sense switching, been making them for 30 years, so I can follow your logic.

Brian

 

[mpo]

Back with additional info. Regulator being used is a Morning Star ProStar 30 which has an additional off take to independantly supply a "load" This supply is controlled by a low voltage disconnect to maintain the battery bank at full charge. Whilst I appreciate that a device like the "FridgeMate" might prove very useful when operating the fridge from the battery supply ( eg overnight ) it would appear to be more efficient to operate the appliance direct from the solar supply whenever possible as you avoid any losses from the natural resistance occuring on passage through the batteries. A straightforward approach would be to manually switch the inputs but an automatic solution might prove less forgetful!!!

Thank you for all your suggestions.

 

[Anonymous]

I have a prostar and large solar panels....good sized domestic batteries and a thermostatically controlled fridge. The fridge only draws around 3A -- and it is a big one, which can pull down to -18C if I set it low.

The fridge is wired direct to the batteries and is on 24/7.

The amount of power the fridge uses has never been an issue for us during nearly five years of cruising.

Are you sure you really have a problem that needs a solution?

 

[whipper_snapper]

[ QUOTE ]
it would appear to be more efficient to operate the appliance direct from the solar supply whenever possible as you avoid any losses from the natural resistance occuring on passage through the batteries.e

[/ QUOTE ]


It just isn't like that! When the reg is dumping power, if you are pulling current 'from the batteries', it is effectively coming straight from the charging system not somehow 'passing through the batteries'. It is the same electricity ! You are just catching it before it goes to the 'spare power' connection!

But you seem determined to set-up some elaborate change-over system, so good luck and have fun. However, IMHO it is certainly possible, but entirely pointless!

 

[noelex]

To improve effencey the best solution is to use the solar regulator to bypass the thermostat when the batteries are full.
This way when the batteries are full the normally wasted solar output (because the batteries are nearing full) is used to get the fridge extra cold. As the solar output drops off during dusk it will revert back to normal thermostat operation, but the fridge wont need to run as much because it has got extra cold when there is excess power. If the next day is cloudy and the solar panels cannot keep up with demand the amp hours that have been drawn out from the battery will be lower and they will last longer.

 

[whipper_snapper]

That's true. You could connect the fridge normally via a V sensitive switch plus use the 'extra' to trigger a super cool by getting it to just close a contact which bypasses the thermostat.

The down side is slightly increased complexity and risk of freezing your beer; which would be a disaster! Maybe get 2 thermostats and switch between them to prevent this disaster but get max coolth?!

 

[Anonymous]

[ QUOTE ]
If the next day is cloudy and the solar panels cannot keep up with demand the amp hours that have been drawn out from the battery will be lower and they will last longer.

[/ QUOTE ]In practice it probably won't work quite like that. While I have fitted an electronic thermistor thermostat effectively across the fridge stat (actually it isn't wired quite like that but that's the effect it has), giving very accurate fridge box temperature control, most fridges still have thermostats that regulate the temperature of the evaporator, not the box. That's why you have to adjust them as the seasons change. So, if the stat is controlling the evaporator to, say, -5C when the box target temperature is, say, +5C then the compressor will always be cycling to maintain that -5C on the evaporator. Suppose you force it on for a while to use available electrical power from the solar panels and suppose the box drops to, say, +3C (that would a bigger effect that you would see in practice in a decent-sized fridge) then you can see that the difference between +3C and +5C is quite small compared with the evaporator temperature of -5C. In my fridge it probably would work OK because I have a thermistor thermostat that measures the actual box temperature at a point that I have determined (some distance from the evaporator plate) but the ordinary fridge stat doesn't work like that.