Solar MPPT with a dump load to a fridge

[gregcope]

Hi All,

Might sound a bit nuts, but if you have say 200AH of batteries and 60W (ish) of Panels - does anyone make a MPPT that has a dump load output that I could rig to start the fridge and cool the beer/wine?

Ie Take any spare once the batteries are good, if the sun is shinning well (ie a nice day) and use that to pre-cool the fridge?

 

[Pete7]

An MPPT controller would be wasted on 60w of panels. Use a PWM controller instead and save the cash for more solar panels.

Pete

 

[silver-fox]

I was attracted to the idea at first - until I realised that the panels do provide charge directly, if the fridge is on a duty cycle. If it's not on a duty cycle its because the fridge is down to temperature - so why would you want to cool it more?

If you did decide to use the surplus in this way you would take the fridge temperature down from <say> 4 degrees to freezing and destroy potentially the contents.

If you want to store surplus energy a more flexible method would be to add another battery to the service battery bank

 

[William_H]

I can see Op point when he reads that some controllers waste solar panel power into a resistor. A typical small fridge might take 4 amps when running.
As said the 60 w panel will produce 3 amps in full sun. So a fridge would soak up all the panel power plus a bit.
The only way I can see to do what he wants is to make or buy a VSR voltage sensing relay which will turn the fridge on when the battery voltage rises to say 14v under charge from the solar panel. it would need to be set up to turn off again at about 13volts. ie turn off when the battery is still well charged. This set up would also be good for running the fridge only when the engine is charging. If we assume the fridge is warm and the boat looking after itself on a mooring then if the battery voltage gets high enough the fridge will turn on to drain the battery a bit so cooling the fridge. I imagine the fridge would pull the battery down long before the thermostat cut in to turn fridge off. So yes OP might have cool beer and a cool fridge if not not very cold. The fridge and VSR would form a controller for the solar panel which could be connected without a regulator. (perhaps) The set up would need to be monitored for actual battery charge outcomes.
good luck olewill

 

[Pete7]

Is there not a risk of the VSR cycling? It is the reason I have the solar panels connected to the house bank rather than the recommended engine start battery. What happened before the change was the solar charged up the engine battery and the VSR then connected in the house bank with a clunk. a two minutes later the voltage in the engine battery had been reduced by the house bank so the VSR dropped out with another clunk. Solar then quickly charged up the engine battery and so it went on. Solved by charging the house bank first before the VSR licks in as the small engine battery won't pull the voltage down. However, with a 3-4 amp hour draw to a fridge that could pull the voltage down quite quickly.

Buying a PWM controller and another battery as suggested by SF rather than then MPPT would enable energy to be stored for use by the fridge during the night.

Pete

 

[RAI]

Why not simply connect the fridge to the controller's load terminals? The controller is likely to have a low voltage battery protection shut-off. It will then depend on the duty cycle and insulation of the fridge as to whether 60Wp PV panels during the day store enough to counteract the 24 hour consumption. A few days of testing will show if more fridge insulation and/or more PV Wp is needed.

 

[VicS]

Why not simply connect the fridge to the controller's load terminals? The controller is likely to have a low voltage battery protection shut-off. It will then depend on the duty cycle and insulation of the fridge as to whether 60Wp PV panels during the day store enough to counteract the 24 hour consumption. A few days of testing will show if more fridge insulation and/or more PV Wp is needed.

ITYWF that many of the cheap solar panel controllers are intended for street lights and have the load output controlled by the solar panel output so that the lights switch on at night and off during the day ..... not what the OP will require.

 

[RAI]

ITYWF that many of the cheap solar panel controllers are intended for street lights and have the load output controlled by the solar panel output so that the lights switch on at night and off during the day ..... not what the OP will require.

Not in the case of either of my controllers, but they are intended for PV panel use. The low battery protection is there to do what it says, shut the load down when the battery voltage drops too low. They both have over voltage protection too, which isolates the panel if the battery voltage gets too high. Mine are set at 11.98v and 14.7v respectively.
I thought the controllers that dump to a resistance were intended for wind turbines.