Voltage sensing relay to control waterheater?

[Franziska]

Hi,

we are looking into adding a voltage sensing relay to our LiFePo4 battery bank which starts the 220V water heater once the battery bank is about 80% full and switches it off again when around 65%.
We'll add a manual switch too, which allows us to stop the automatism when not needed.

Currently we do this by hand, but if there is a cheapish simple solution we'd love to install it.

As the BMS, battery, solar controllers and everything is already installed and working fine we do not want to change any of those parts.

We prefer a low budget solution and appreciate it, if someone can suggest/link to a suitable relay.
We also prefer a simple solution without tons of features like Bluetooth and so on.

[fxykty]

I guess you are looking for a generic VSR whose output (active for a certain voltage range corresponding to your desired SOCs) would provide the input to an SSR. Something like this https://www.sensata.com/sites/defaul...-datasheet.pdf. The SSR output connects or disconnects the water heater load wire.

[Franziska]

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

[smac999]

The problem is lith voltage is pretty steady. You need to use Soc. Not voltage. Plus if you have solar the voltage readings are out the window. Because you could be at 50% Soc with higher voltage. Plus when the heater turns on the voltage will drop

I’m pretty sure a relay in a victron bmv can do this. It can turn on / off at a certain Soc. But I’m not sure if you can cycle between 2 different Soc vaules. You would need another relay in the ac line to be controlled by the bvm.

[Franziska]

Originally Posted by smac999

The problem is lith voltage is pretty steady. You need to use Soc. Not voltage. Plus if you have solar the voltage readings are out the window. Because you could be at 50% Soc with higher voltage. Plus when the heater turns on the voltage will drop

I’m pretty sure a relay in a victron bmv can do this. It can turn on / off at a certain Soc. But I’m not sure if you can cycle between 2 different Soc vaules. You would need another relay in the ac line to be controlled by the bvm.

Good points. Thank you.

Though we do not have Victron and will not get Victron. Surely it's a nice piece of kit but it's super expensive too.
As stated, we have a solar & LiFePo4 system which works good and will not start replacing parts of it.
If that would need to happen we will rather continue switching by hand.

[smac999]

A bvm is like $200. Peanuts for a boat. What do you currently use as a battery monitor?

[RaymondR]

Some solar relays include a load terminal which is programmable and whilst they usually are not sufficiently powerful enough to directly drive an inverter they would drive a relay.

Some inverters also include provision for a remote on/off switch which could be cycled by a fairly low power relay.

[Franziska]

Originally Posted by smac999

A bvm is like $200. Peanuts for a boat. What do you currently use as a battery monitor?

200$ is a lot of money and not peanuts at all.

Daly BMS, 3x Epever charge controller and a simple Coulomb meter.

[Franziska]

Originally Posted by RaymondR

Some solar relays include a load terminal which is programmable and whilst they usually are not sufficiently powerful enough to directly drive an inverter they would drive a relay.

Some inverters also include provision for a remote on/off switch which could be cycled by a fairly low power relay.

Good comment. Thank you. Will look into this, I think our Epever have this option.

[chris mac]

We have the victron bms. We have the parts to set up an excess power dump into the hot water but haven't set it up yet.
Basically it is a virtual load relay. You set the bms to switch on at a custom set voltage, say 14.3 since bulk and absorption are set to 14.4
And to switch off at another voltage.
You wire the hot water tank thru the switch, to the battery. And the switch relay to the bms.
So Im guessing you can do something similar with your system. Victron just makes it easy

[goboatingnow]

How can you dump excess PV into hot water. Have you a dc water heater ?

If you use invertors you’ll need a proper columb counting battery monitor to switch on the invertor.

In my case I interlock the BMV712 output with the mppt load relay so my water heater invertor only triggers when I have sun and a full battery

[chris mac]

Originally Posted by goboatingnow

How can you dump excess PV into hot water. Have you a dc water heater ?

If you use invertors you’ll need a proper columb counting battery monitor to switch on the invertor.

In my case I interlock the BMV712 output with the mppt load relay so my water heater invertor only triggers when I have sun and a full battery

It's very easy and cheap to change the water heater element to a dc model. Mine is 300watt 12 volt. Bought on Amazon for around $13.

[goboatingnow]

Originally Posted by chris mac

It's very easy and cheap to change the water heater element to a dc model. Mine is 300watt 12 volt. Bought on Amazon for around $13.

Yeah. I trying that out over the winter however it could take a long time to heat anything at 300 watts. But it’s worth an experiment

Currently the invertor option does provide the best of both worlds and interlinked with the “ load “ relay on the mppt controller and the SOC relay on the BMV712 means I can use excess solar only. ( well it still hits the battery hard anyway )

I currently just use a cheap Chinese modified sine wave invertor dedicated solely to the immersion ( I beefed up its fans seriously an added temp monitoring )

I’m transferring the trigger controls to purely digital over the winter as I’m networking my BMV and MPPT so I can release thd rather crude relay method

[OldGreyB]

While this does not address the OP question directly with respect to an Automatic SOC control, this is how our Solar Hot Water cycle operates while providing (AGM) battery protection.

We activate a manual impulse switch whenever then Solar charged battery bank are at or better than 80 SOC. The action of manually clicking the impulse switch on our auxiliary electrical panel, runs a digital timer relay set for 54 minutes. https://www.ebay.com/itm/19371034589...is&media=EMAIL The output of the digital timer relay turns on the 12vdc coil of the 230Vac water heater load Phoenix brand commercial DIN rail relay, which supplies 230VAc power to the 1200watt water heater element via the already on invertor. The digital time is set to exceed the time to bring the water from ambient temperature to the full thermostatic controlled "off" temperature, while ensuring the waterheater draw battery load is a finite amount. An LED on our auxiliary electrical panel shows when the Solar Hot Water cycle is operating.

Our control circuit includes a 12Vdc victron under-voltage protection for battery protection https://www.victronenergy.com/batter...attery-protect . If battery bank under-voltage is sensed during the Solar Hot Water cycle period, the unit disconnects the 12Vdc coil voltage of the 230Vac relay supplying 230Vac to the Hot Water cylinder This automatically resets on again when battery voltage returns during the Solar Hot Water cycle period. This protection may trigger if galley 230Vac usage via the inverter is high while the Solar Hot Water cycle is operating, i.e galley loads take preference over water heating.

We click this impulse switch daily when onboard, and the 40L water heater provides sufficient hot water for our daily needs. The 12Vdc digital timer, impulse switch, indication LED plus the 230V load relay were inexpensive, the Victron battery protection module was around $60AUD.

For the OP, maybe you can incorporate some of above with your Epever charge controller , providing what you need without too much complexity, but still make your waterheating semi automatic.

[smac999]

those of you running low wattage heaters or only running the tank short periods each day will excess solar. keep in mind a warm hot water tank is dangerous to you. you do need to get the tank to full hot temperatures to kill off bacteria in the tank.

https://homeguides.sfgate.com/turnin...ria-54596.html