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paul-w asked

Solar dump load via SmartSolar chargers

On our motorhome I have 250 watts of solar going through a Victron SmartSolar 100/20 and 160 watts of solar going through a Victron SmartSolar 75/15.

When our 240Ah LifePo4 battery is fully charged, which in summer months is about 10.30 - 11 am in the morning then the solar is no longer being harvested, so I want to harvest more solar via the load terminals on the SmartSolar chargers to heat water.

My question is, can I join the two load output from both the solar chargers and and send it via one cable to power the water heater element, in other words, although different outputs, will the two share the loads without damaging the chargers.

The water heater element is 12v 300watts and I have tested it with a battery and draws 25,3 amps which is what I would expect. The likelihood of the solar panels giving their maximum quoted output is unlikely, so can I take this into account.

If push comes to shove, then I can split the loads as the water heater element is two 150 watt elements joined, but I'm trying to save on cabling.

MPPT Controllers
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2 Answers
Jesse avatar image
Jesse answered ·

I would suggest just using the load output of one to switch a relay. The MPPT's aren't designed to switch large loads, and will quickly disconnect if they detect anything too high. 25 amps is close enough to the combined maximum that unless perfectly shared it is likely one MPPT would see enough current to disconnect, then the remaining MPPT would have to face stopping the full 25 amps on it's own - a likely damaging situation if the fuse doesn't blow.

Also, beware the losses when trying to carry large amounts of DC current, losses tend to be very high. Sometimes better to boost to 240V despite the risks associated.

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ripper avatar image
ripper answered ·

Use a relais or battery protect or other ssr solid state relay driven by the load output. You likely will not sustain neither one nor two times 150W via solar with this setup. So either the battery will help out and be drained or very short cycles will occur as the load output can only look at voltage levels.

Consider playing with stringing heating elements or switchable depending on weather. Putting them in series might get power consumption down to a quarter. This can be sustained not only in peak midday sun and since you have all day that might be the way to go.

Bonus points for PWM driving a ssr depending on sunshine ;)

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