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Inverter for water heater


trialsrider

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As mentioned earlier on previous posts I'm fitting an 850w truma electro boiler to add hot water to my van. As everytime we go away we use hook up but I was wondering about the rare chance I may get to wild camp without family and without hook up.

 

I realise you would need immense battery power to invert 12v DC to AC to heat 850w. But what about with engine running?

 

If the inverter was only for the water heater to plug into and nothing else, could my DC set up power it.

 

Would appreciate if someone with inverter knowledge could tell me if it's possible.

 

I have a 100ah leisure battery, 160w solar and a 30amp split charge. The water heater would have to run for 60 minutes for water to go from 15 degrees to 70.

 

Could an inverter be used to achieve this with engine running and if so what size and type ?

 

And before anybody suggests why don't I go down the gas route it is because of heater location, ease of installation and unlikelyness of not being on hook up. The inverter option is just a consideration.

 

 

 

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Short answer is that its not practical idea.

 

For an inverter to deliver 850 watts it will draw something like 80 amps from a 12v battery and a bit less if there is alternator charge. So connecting an inverter direct to the engine battery with the engine running, could be considered. If the existing VSR were to be updated to a 180A, unit with substantial cables to the leisure battery, then the inverter could be connected there. ( in any event I advise up rating from a 30A VSR.)

Although taking 80 A from the alternator is possible, ( the OEM is rated at least to150A maximum), it could introduce reliability issues. Peugeot/Citroen provide a 50A fused circuit for the converters outlet, so this suggests that 50 A is an allowable value. All things considered I would not recommend having an inverter taking 80A from the alternator in this application.

 

You could consider using an inverter configured for 110 v ac, that would halve the power taken by the heater ( the heater circuits would need some investigation to confirm there would be no undesired side effects).

 

A water heater that could be operated from alternator power with least complexity is the Surecal heater with a 300 watt 12v heating element,

 

https://www.surejust.co.uk/6-litre-12v-240v-motorhome-water-heater.

 

Mike

 

 

 

 

 

 

 

 

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Bearing in mind your statement that this is a contingency plan for rare circumstances, I don't think this is a remotely sensible or practical idea either. And the inverter necessary to carry the electrical load would be a big lump of otherwise useless kit to be carrying around too.
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You will need app 26 amps @ 12 volt d.c. to produce 1 amp @ 240 volt a.c. And kill your batteries. And running you engine on tickover for an hour is not good for it. I used to run my inverter from the engine battery, this allowed me to run the onboard charger whilst driving which gave a good rate of charge. But I wouldn’t recomend it for what you are contemplating.
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mikefitz - 2020-10-18 3:28 PM

 

=====================================================================================

 

You could consider using an inverter configured for 110 v ac, that would halve the power taken by the heater ( the heater circuits would need some investigation to confirm there would be no undesired side effects).

 

=====================================================================================

 

Mike

 

 

I am sorry Mike, but I cannot agree with the above section of your otherwise excellent summary.

 

Reducing the voltage to 110V, from for simplicity 220V, will reduce the power consumed by the heater to one quarter of the power taken at 220V. As you will realise, assuming constant heater element resistance, power dissipated is proportional to V x V, or V squared.

 

I am experimenting with using a 115V alternator powered inverter, to supply the 450W water heating element in my Truma Combi. The idea is not to heat the water, but to compensate for heat loss from preheated water when travelling.

 

Alan

 

Alan

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tonyishuk - 2020-10-19 7:46 AM

 

Passing thoughts !

 

It is possible to get heater units for gas and 12 /24 volt for installation in dog daycare and horse boxes

 

Depending on how much hot water you need and how warm, 12 b 24 volt cup / mug heating element for lorries might help.

 

Rgds

 

Hi there. The water heater is mainly for showers so I need a high litre heater. I did look at the elgena nautic therm which had a 20 litre model, 12v and 240v combined elements. However I didn't like the strap fixing method these heaters use and they had a 12 week lead time. Oddly too for a German company their customer service communication was poor. So I plumped for the truma.

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Alanb - 2020-10-18 6:38 PM

 

...I am experimenting with using a 115V alternator powered inverter, to supply the 450W water heating element in my Truma Combi. The idea is not to heat the water, but to compensate for heat loss from preheated water when travelling.

 

Alan

 

A basic problem with retaining the hot water temperature of Truma Trumatic-C appliances (like yours) and the follow-on “Combi” heaters is that their water boiler has little external insulation, unlike Truma’s 14 litres 230V water heater that is very heavily insulated to slow heat loss.

 

At least the ‘heating collar’ principle used for 230V water heating with Trumatic-C appliances (except for the C-6002EH model) means that you can experiment without it impacting on the rest of the heater, and the collar itself still seems to be obtainable (£350-£400)

 

It will be interesting to learn how you get on with your inverter approach.

 

This 2008 forum thread discussed various ways to heat ‘domestic’ water while travelling

 

https://forums.outandaboutlive.co.uk/forums/Motorhomes/Motorhome-Matters/Hot-Water-Heat-Exchanger/10242/

 

 

 

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If you intend to go off hook up during the summer months then the bag type solar showers are very good, we use them quite often in preference to the caravan shower when we've been on the beach and have a small utility tent set up for showering.

 

However they're only practical in hot weather B-)

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  • 2 years later...
On 10/18/2020 at 5:07 PM, weldted said:

You will need app 26 amps @ 12 volt d.c. to produce 1 amp @ 240 volt a.c. And kill your batteries. And running you engine on tickover for an hour is not good for it. I used to run my inverter from the engine battery, this allowed me to run the onboard charger whilst driving which gave a good rate of charge. But I wouldn’t recomend it for what you are contemplating.

  HI

Sorry if  revive a corpse here

I was looking in to a calorifier heater of 20 L but am a bit wary of taping into my cooling system like this video below. And I was thinking of the inverter option and doing this electric. 

Now i would not have the engine ticking over for it but I do not tend to be stationary for more than 28 h and could heat while driving.

I don't understand inverters and the load on the alternator though.

So the house battery get charged by

1)  Alternator while driving via DC-Dc/mppt controller
2) That rare golden object in the sky during daytime while stationary via DC-Dc/mppt controller

Now an inverter

A) Could be connected to a housebank and suck it dry in quicker than a starved crack whore looking for protein
B) Connected to inverter/car battery ...BUT preferably not with engine ticking over

So in scenario 

1+B... I am driving along at 55mph after being parked up for 48-72h (and my fridge and vent having depleted my bank to 60%) ... I also want to heat my HW tank via the inverter ...If I switch the power to inverter on and would start heating water (The only function this inverter would have) 

How would this affect

1: The charging of my house bank
2: The Alternator
 

 

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If the inverter is only for hot water heating then I would question as to why you want to heat water that way, if its for 'free' hot water that doesn't work, as any power you take from alternater loads the engine more and uses more fuel, tapping into the engine cooling system however uses waste heat (at least when engine is up to temperature) and the only cost is initial outlay. 

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