Voltage sensing relay to control waterheater?

[chris mac]

Smac
I understand, and mostly agree with what you are saying. But as your article says, 95 to 115 degrees f is where bacteria grows. That is tropical air temps. All your waterlines are in that temp zone.
As far as low wattage elements go, yes you need to run them for a longer period of time to achieve the same temp increase. The advantage of low wattage is it can run solely on incoming solar. Once we hit absorption mode, usually around 1pm, we can turn on the water heater and run it at least a couple hours per day.
All that said, the best way to avoid bacteria growth is flow. Use that water up and replenish with fresh, clean water.

[goboatingnow]

Originally Posted by chris mac

Smac
I understand, and mostly agree with what you are saying. But as your article says, 95 to 115 degrees f is where bacteria grows. That is tropical air temps. All your waterlines are in that temp zone.
As far as low wattage elements go, yes you need to run them for a longer period of time to achieve the same temp increase. The advantage of low wattage is it can run solely on incoming solar. Once we hit absorption mode, usually around 1pm, we can turn on the water heater and run it at least a couple hours per day.
All that said, the best way to avoid bacteria growth is flow. Use that water up and replenish with fresh, clean water.

I treat all my water with Milton tablets any way.

[betwys1]

Originally Posted by Franziska

Thank you. Looks like this is exactly what we need :-)

The fxykty suggestion appeasrs to be a solid state relay. Not what you need, I don't think.

https://www.keylinechargers.com/prod...pr_seq=uniform

This purports to be a voltage sensing relay suitable for LiFe cells but I am doubtful - you need capacity sensing not voltage sensing.
I spent way too much time reviewing coulomb counting / state of charge devices, and get a sense there may be usable devices under $50 but I think you need actual user experience with a device to be more confident. Sorry!

[drdoyle]

Never use a battery to heat water (well maybe for a quick coffeepot - but microwave is faster) . If you want hot water use engine fw cooling loop heat exchanger. Or straight solar direct water heater. You could try a direct solar panel dc to heater coil, but I doubt you could get enough amps to raise the temperature more than 10-20 degrees F in daylight..

[Franziska]

Originally Posted by drdoyle

Never use a battery to heat water (well maybe for a quick coffeepot - but microwave is faster) . If you want hot water use engine fw cooling loop heat exchanger. Or straight solar direct water heater. You could try a direct solar panel dc to heater coil, but I doubt you could get enough amps to raise the temperature more than 10-20 degrees F in daylight..

We, the thread opener have a thermosolar heater, but we also have lots of solar and battery power. We have no inboard engines.
Our thermosolar is hooked to the heat exchanger of the calorifier. Sometimes we do have excess battery power. Nothing wrong with dumping the excess into the water heater when the batteries are 95% full. Be it via inverter and 220V heating cartridge or via a 12V heating cartridge. Undecided yet.
Our solar & battery power is so big because we sometimes need it for running our business. But not always..

[Pete7]

Franziska, I can't help think that your current system of doing it via an inverter and manually switching it perhaps with a £5 clockwork kitchen timer is way cheaper and simpler.

There is a French firm that make a widget, but It think its voltage controlled, so don't know how that will work with LFP. Chris the ower may be a member on here. However, its a E200 widget:

https://www.green-yachting.online/yacht-hot-water

Actually, when you say "using surplus solar" it doesn't matter. Say you want a shower in the morning but the LFP batteries are at 60%. Run the water heater for an hour might take them down to 35%, but it doesn't matter with LFP. Solar will charge them up during the day.

The problem and its difficult is getting use to, is the idea of not needing to charge to 100%. Its taken us a while. The lowest we have been down to is 33% when I baked a cake one morning. little solar as it was raining, but didn't worry and the sun eventually appeared in the afternoon.

Pete

[Cowpoos]

I would use a cheap adjustable low voltage disconnect module/board. Adjust the disconnect voltage to maybe 13.7 volts for LiFePo4, and then when above 13.7 volts the relay will turn on connecting power to the water heater and when below this disconnect. I'm sure you could find what you need for $5 or so on Ebay or Aliexpress.