How to wire my hot water heater to two AC sources?

[Brendan]

Hi All,

Am hoping someone will be able to offer me some advice about how to wire up my hot water heater so it can be powered either by the generator, when it is running, or by my inverter using a 30 min countdown timer switch.

Current set-up:
1,200 amp hour LiFePo4 house bank connected to a Victron Quattro 5000 inverter charger. Hot water heater is currently wired up to one of the Quattro's AC outputs that is only live when Quattro receives AC power from either shore power or generator. This is wired so as to avoid accidently draining the house bank if one forgets to turn off the hot water heater at the switchboard.

Target Set-Up:
Since I have 1,600 watts of solar and the water gets hot after about only 30 min of shore or generator power, I bought a mechanical 30-min countdown timer switch (https://www.amazon.com/dp/B003FIYZRI...roduct_details). I'd like to wire this up to the Quattro's other AC output that is fed by the inverter and so live even when there is no shore power and the generator is not running. The idea is to avoid needing to fire up the genset just to heat hot water and instead simply turn the knob on this countdown timre to 30 min to get hot water without the risk of accidently draining my house bank.

What I'm wondering about is if it would be safe and wise to simply wire up the imersion heather to both output circults at the same time, or if that would risk doubling up the AC voltage and frying my impersion heater (or damagaing the Quattro)? Is there a smarter way to get to the same outcome?

I could obviously disconnect the imersion heater from the Quattro's output that is live when shore power / genset is available, and have the imersion heater only wired to the countdown timer, but then I'd need to remember to turn on the count down timer for hot water even when I am on shore power or the genset is running.

Thanks in advance for any advice an appologies if this is a dumb question, AC power is mysterious to me.

[s/v Jedi]

Originally Posted by Brendan

Hi All,

Am hoping someone will be able to offer me some advice about how to wire up my hot water heater so it can be powered either by the generator, when it is running, or by my inverter using a 30 min countdown timer switch.

Current set-up:
1,200 amp hour LiFePo4 house bank connected to a Victron Quattro 5000 inverter charger. Hot water heater is currently wired up to one of the Quattro's AC outputs that is only live when Quattro receives AC power from either shore power or generator. This is wired so as to avoid accidently draining the house bank if one forgets to turn off the hot water heater at the switchboard.

Target Set-Up:
Since I have 1,600 watts of solar and the water gets hot after about only 30 min of shore or generator power, I bought a mechanical 30-min countdown timer switch (https://www.amazon.com/dp/B003FIYZRI...roduct_details). I'd like to wire this up to the Quattro's other AC output that is fed by the inverter and so live even when there is no shore power and the generator is not running. The idea is to avoid needing to fire up the genset just to heat hot water and instead simply turn the knob on this countdown timre to 30 min to get hot water without the risk of accidently draining my house bank.

What I'm wondering about is if it would be safe and wise to simply wire up the imersion heather to both output circults at the same time, or if that would risk doubling up the AC voltage and frying my impersion heater (or damagaing the Quattro)? Is there a smarter way to get to the same outcome?

I could obviously disconnect the imersion heater from the Quattro's output that is live when shore power / genset is available, and have the imersion heater only wired to the countdown timer, but then I'd need to remember to turn on the count down timer for hot water even when I am on shore power or the genset is running.

Thanks in advance for any advice an appologies if this is a dumb question, AC power is mysterious to me.

If you connect it to both outputs, you short the outputs, undoubtedly leading to expensive repair bills.

You already bought the timer switch so that’s what you have. If it doesn’t have an always-on position then you don’t have that.

I would have bought a Shelly relay that uses an app or even a browser to control it over wifi. There are many options.

[Brendan]

Originally Posted by s/v Jedi

If you connect it to both outputs, you short the outputs, undoubtedly leading to expensive repair bills.

You already bought the timer switch so that’s what you have. If it doesn’t have an always-on position then you don’t have that.

I would have bought a Shelly relay that uses an app or even a browser to control it over wifi. There are many options.

Thanks very much! I definately won't wire up both AC outputs then. Checked out Shelly switches, interesting. Fundamentally though, it appears as if I can only use one of the AC sources, unless I used a relay and a third switch to toggle between the two sources, making things even more complicated. Sigh.

[s/v Jedi]

Originally Posted by Brendan

Thanks very much! I definately won't wire up both AC outputs then. Checked out Shelly switches, interesting. Fundamentally though, it appears as if I can only use one of the AC sources, unless I used a relay and a third switch to toggle between the two sources, making things even more complicated. Sigh.

A Shelly relay, as well as many smart outlet adapters, let’s program you an automatic shut down after a set time. Also it allows you to program schedules etc.

At worst case, when it isn’t smart enough, you have to tap the screen on your phone or tablet to switch from timer to always on or off mode.

Of course this requires knowledge on programming such devices, connecting them etc. You can even drive the on/off function based on a signal from the battery monitor when that has a programmable relay, like the Victron BMV. For exmp,e, when battery SOC is more than 90% etc. Also, solar MPPT controllers often have relay outputs to control such things.

[PippaB]

A simple double-pole, double-throw relay (even a single-pole, double-throw if you are not running split-phase and your neutrals are all common) with an AC coil to match your shore power voltage would do the trick.

Wire the common to the water heater. Wire the normally closed to the timer, which then goes back to the inverter output (as you already have it). Wire the normally open to the shore/gen output from the inverter. Wire the coil also to the shore/gen connection.

When the gen/shore is live the coil will be energized, the contacts will pull in, and power will flow from gen/shore through the NO contacts (that are now being held closed by the coil) and to the heater element. The inverter output will be disconnected from the heater. When shore/gen goes away the coil will release, the contacts will transition, and the heater will be connected to the output of your timer switch, which you can then turn to run when the solar is abundant and the batteries are tapering their charge.

All automatic except for turning the timer whenever you want to heat from the inverter. You are basically making a small scale automatic transfer switch.

They cost a bit more, but I personally prefer hermetically sealed relays on the boat. Will depend on the current requirements of your heater whether they are a viable option.

Edit:

No affiliation, and I have not reviewed it for details (for instance, is your boat 120V? or 240V?), but if you just want to buy something...

https://www.amazon.com/gp/product/B0...JJFWBFD7&psc=1

[skipperpete]

Brendan, your statement “AC power is mysterious to me” was reason enough to get the electrical work done by a licensed professional electrician and not follow the advice of random forum members regardless of how confident and informed they might sound. I have no knowledge of the legalities concerning AC work done by unqualified persons in the US or how such work might be interesting to to an insurance company but I do know that in Australia, a death caused by illegally installed AC wiring will involve police charges and an inquest even if its a fire caused by the wiring.

[Bowdrie]

^ One of the things I've learned on this forum is that it seems to be that in Australia you need a licensed/bonded professional to change a lightbulb.

[TrentePieds]

Well, you can add Canada to that!

You can do wiring in your own home - if it is a "detached House" . If your home is in a "multi-family building" you can't touch ANYTHING unless you are "trade qualified"!

That is IMO as it should be!

TrentePieds

[Brendan]

Originally Posted by PippaB

A simple double-pole, double-throw relay (even a single-pole, double-throw if you are not running split-phase and your neutrals are all common) with an AC coil to match your shore power voltage would do the trick.

Wire the common to the water heater. Wire the normally closed to the timer, which then goes back to the inverter output (as you already have it). Wire the normally open to the shore/gen output from the inverter. Wire the coil also to the shore/gen connection.

When the gen/shore is live the coil will be energized, the contacts will pull in, and power will flow from gen/shore through the NO contacts (that are now being held closed by the coil) and to the heater element. The inverter output will be disconnected from the heater. When shore/gen goes away the coil will release, the contacts will transition, and the heater will be connected to the output of your timer switch, which you can then turn to run when the solar is abundant and the batteries are tapering their charge.

All automatic except for turning the timer whenever you want to heat from the inverter. You are basically making a small scale automatic transfer switch.

They cost a bit more, but I personally prefer hermetically sealed relays on the boat. Will depend on the current requirements of your heater whether they are a viable option.

Edit:

No affiliation, and I have not reviewed it for details (for instance, is your boat 120V? or 240V?), but if you just want to buy something...

https://www.amazon.com/gp/product/B0...JJFWBFD7&psc=1

Thanks very much PippaB - really appreciate your advice. My boat has 230v AC - not sure if split phase or not, and not sure how to find out.

I'd need to find a 230v AC version of that Automatic Transfer Switch, will have a look to see if I can find one.

[Brendan]

Originally Posted by skipperpete

Brendan, your statement “AC power is mysterious to me” was reason enough to get the electrical work done by a licensed professional electrician and not follow the advice of random forum members regardless of how confident and informed they might sound. I have no knowledge of the legalities concerning AC work done by unqualified persons in the US or how such work might be interesting to to an insurance company but I do know that in Australia, a death caused by illegally installed AC wiring will involve police charges and an inquest even if its a fire caused by the wiring.

Thanks for that advice, I may end up doing that. I've wired up my electric galley stove and 230v AC watermaker myself to my switchboard, so may have overstated my uncertainty about electrical topics. The Automatic Transfer Switch PippaB mentioned may be the way to go, will research that and if I get stuck hire an electrician.

[CrispyCringle]

Why is the water heater not wired through the main breaker panel with its own switch/breaker? A well designed panel will not allow multiple AC sources at the same time, and problem solved.

[Madehn]

“Why is the water heater not wired through the main breaker panel with its own switch/breaker? A well designed panel will not allow multiple AC sources at the same time, and problem solved”.
+1

[Madehn]

Do they make a dual element heater element that fits your unit. If so you can wire one part to the ac and the other to a dc circuit and totally bypass your inverter and it’s inefficient portion of the circuit

[Brendan]

Originally Posted by Madehn

“Why is the water heater not wired through the main breaker panel with its own switch/breaker? A well designed panel will not allow multiple AC sources at the same time, and problem solved”.
+1

The 230v AC imersion heater _is_ of course wired to a breaker on the main breaker panel with its own switch/breaker. That breaker is however only suppied power when the boat is on shore power or the genset is running.

The objective is to to be able to either

a) power the 230v AC impersion heater via a 30-min count-down timer with 230v AC from the inverter, so I can heat water from the battery / solar power - without having to worry about someone running the battery empty

and/or

b) (continue) to power the 230v AC impersion heater all the time when the boat is on shore power or the genset is running.

[Madehn]

So wire the inverter thru a transfer switch to the panel and you are done. When the transfer switch senses AC power from another source it trips and cuts the inverter off. Another cheaper solution is to wire a large high voltage rotary switch that controls input to your panel. Off Shore Generator Inverter. This is simple and prevents more than one source from powering your panel. This is what I have on my boat with a second rotary switch to choose beteeen inverter 1 and inverter 2. Both are inverter chargers and it is wired so that I can push 250 amps of charge into batteries if I wanted to by running both chsrgers and using either shore or generator as the source. The rotary switches are large and be prepared to spend some time mapping out the flow with a multimeter before wiring it up. Not hard but takes time. Once done is bulletproof in that you cannot accidentally select more than one source of ac at a time and you cannot fry your inverters by backfeeding current to their outputs. Good luck