Probably a daft electrical, battery/alternator question

[casper ghost]

Hi. I only have 1 115ah domestic battery, but I'd like to run a small immersion heater, probably a 12 v one. My battery bank won't be up to it, but, if I only ever use it with the engine running, will it run off my alternator, it's a fairly standard alternator, think 70 or 75 amp. I just didn't know if alternator going through the battery would then run the immersion heater, which is probably about 600 watts 12v. It's either that or use a 240v and start a Genny...

Thanks.

[Tracy D'arth]

12 minutes ago, casper ghost said:

Hi. I only have 1 115ah domestic battery, but I'd like to run a small immersion heater, probably a 12 v one. My battery bank won't be up to it, but, if I only ever use it with the engine running, will it run off my alternator, it's a fairly standard alternator, think 70 or 75 amp. I just didn't know if alternator going through the battery would then run the immersion heater, which is probably about 600 watts 12v. It's either that or use a 240v and start a Genny...

Thanks.

600w at 12v is at least 50Amps. If you have a 50A alternator you will cook it very quickly. If you have a bigger alternator which is highly unlikely with one 115Ah battery then you may run it for a short while until the battery goes low. It will then take you much much longer to put that charge back into the battery.

Are the cables on the heater and in the boat capable of passing 50A without burning, fusing or having so much voltage drop that it works badly?

Running heating sources from batteries is a pointless pastime. 

[Paul C]

P = V x I so in theory, yes. BUT why? Does the calorifier not have a circuit from the engine coolant? If you did go down the 12V route, the wires to and from the immersion heater would need to be some significant size to be able to cope with that current on a continuous basis.

[magnetman]

Also a 600watt immersion heater is going to take a long time to heat water. 

 

How big is the clorifier and someone will be able to do the math. 

[casper ghost]

Ok, so 12v doesn't sound good. I used to have 2 domestic batteries, but I just have 1 now as my usual electric consumption is very low. The alternator is 70 or 75 amp. 

Just now, magnetman said:

Also a 600watt immersion heater is going to take a long time to heat water. 

 

How big is the clorifier and someone will be able to do the math. 

10 gallon, so a fairly little one. 

[Tracy D'arth]

One 115Ah battery trying to supply 50+Amps will not last long before it is useless, boiled and needing replacement.

 

Best advice?  Don't do it.

 

 

[magnetman]

What engine is it?

[Alan de Enfield]

25 minutes ago, casper ghost said:

Hi. I only have 1 115ah domestic battery, but I'd like to run a small immersion heater, probably a 12 v one. My battery bank won't be up to it, but, if I only ever use it with the engine running, will it run off my alternator, it's a fairly standard alternator, think 70 or 75 amp. I just didn't know if alternator going through the battery would then run the immersion heater, which is probably about 600 watts 12v. It's either that or use a 240v and start a Genny...

Thanks.

 

It'll be a very expensive way of heating a calorifier full of water.

 

To Heat 1 litre of water by 10C = 105Wh (.105Kwh)

 

1 litre of water by 60 degrees = 105Wh x 6 = 630Wh 

 

So with your 600 watt heater it will take ~1 hour for each litre you want heating

 

If your engine uses 1 litre of diesel per hour (£1.50 ?) then it is going to cost you ~£1.50 per litre.

 

Assuming your calorifier is plumbed in to the engine circuit you will of course get heat from that, which will reduce the time you need to use the immersion heater.

 

 

Edited April 9, 2023 by Alan de Enfield

[magnetman]

1 minute ago, casper ghost said:

Ok, so 12v doesn't sound good. I used to have 2 domestic batteries, but I just have 1 now as my usual electric consumption is very low. The alternator is 70 or 75 amp. 

10 gallon, so a fairly little one. 

 

This is going to take a long time to warm with a 600w element. 

 

Other question is what is the calorifier currently heated by? 

 

It seems odd to have one on a boat and for it to not be connected to the engine cooling circuit. 

Is this a Neverspacher problem?

[casper ghost]

3 minutes ago, magnetman said:

What engine is it?

Ruston and Hornsby 1VSH. It won't get hot unless I'm cruising.

[magnetman]

Ah OK..Stationary hot water. 

 

Wash less often ?

 

 

[casper ghost]

5 minutes ago, magnetman said:

 

This is going to take a long time to warm with a 600w element. 

 

Other question is what is the calorifier currently heated by? 

 

It seems odd to have one on a boat and for it to not be connected to the engine cooling circuit. 

Is this a Neverspacher problem?

The calorifier used to be heated with the engine, but since I changed the engine I haven't plumbed it in. The new/older engine doesn't get very hot unless I'm cruising. I'm now looking at ways to get hot water for the bath. Yesterday I just boiled pans of water but it'd be nice to have hot water.

2 minutes ago, magnetman said:

Ah OK..Stationary hot water. 

 

Wash less often ?

 

 

That was always fine for me but not the young lady 😂

[magnetman]

5 minutes ago, casper ghost said:

The calorifier used to be heated with the engine, but since I changed the engine I haven't plumbed it in. The new/older engine doesn't get very hot unless I'm cruising. I'm now looking at ways to get hot water for the bath. Yesterday I just boiled pans of water but it'd be nice to have hot water.

That was always fine for me but not the young lady 😂

Ah.

 

You have a lady. OK. This is quite a technical issue which can take a number of yars to resolve. I've been there have the kids and the tee shirt. 

 

Be cautious and wash less often is my considered advice on this matter

 

What calorifier ? There is a hole in it ! 

 

Get the bailer out. 

 

 

 

[Alan de Enfield]

Your only practical solution is to get the genrator out, put as big an immersion into the tank as your genny will support and run the genny for a couple of hours and pay the cost (£4-£5) per time for 40 litres of water.

 

I't be cheaper to go to the local swimming baths or sports centre and get a bath / shower there.

[Paul C]

31 minutes ago, Tracy D'arth said:

One 115Ah battery trying to supply 50+Amps will not last long before it is useless, boiled and needing replacement.

 

Best advice?  Don't do it.

 

 

But the battery isn't supplying the current, the alternator would be....

[Alan de Enfield]

2 minutes ago, Paul C said:

.................., the alternator would be....

 

Not for long it wouldn't be.

 

You meat sacks do have comprehension problems at times.

 

AI rules OK !

[roland elsdon]

So no one has done this  ? Well I have.

No room for a decent calorifier or instantaneous heater, aircooled engine, no room for a heating coil from fire.

So we have a 12v 10 litre calorifier.

It is 300w at 12v or 1000 at 240 but we have no mains on the boat.

 

We have 3 110 batteries including the start and once boating and the advec has stopped , put on the hot water.

The buffer of the batteries means the charge rate is about 25 amps.

We turn the heater off 30 mins before tying up

The alternator ( 127 60 amp)  has sustained this abuse for 4 years to date.

I rewired to match the load with seperate cables.

 

We never heat water unless under way .

 

It works ok, not ideal but pragmatic.

[magnetman]

I think looking at the engine cooling system might be interesting. Undercooled engine is never a good idea specially with an older type. 

 

Restrict the flow of coolant and let it get hot seems wise. 

2 minutes ago, roland elsdon said:

So no one has done this  ? Well I have.

No room for a decent calorifier or instantaneous heater, aircooled engine, no room for a heating coil from fire.

So we have a 12v 10 litre calorifier.

It is 300w at 12v or 1000 at 240 but we have no mains on the boat.

 

We have 3 110 batteries including the start and once boating and the advec has stopped , put on the hot water.

The buffer of the batteries means the charge rate is about 25 amps.

We turn the heater off 30 mins before tying up

The alternator ( 127 60 amp)  has sustained this abuse for 4 years to date.

I rewired to match the load with seperate cables.

 

We never heat water unless under way .

 

It works ok, not ideal but pragmatic.

He wants to heat the water while moored up and apparently the engine does not get up to temperature. 

[Paul C]

I guess it comes down to, 1) what is the actual, continuous, rating of the alternator. I didn't probe further and simply took the 70A given in the OP as a continuous rating, and that the alternator is able to perform properly; and 2) making a lot of other assumptions such as the wiring, fuses etc would be specified and installed properly, to allow for safe continuous running.

 

If we are honestly saying the alternator stated output needs to be derated for a continuous load, the question is, how much by?

 

I have done similar too, albeit for a microwave not an immersion heater, but it wasn't really a continuous load in the same sense as an immersion heater would be running for hours, potentially.

[Alan de Enfield]

2 minutes ago, Paul C said:

If we are honestly saying the alternator stated output needs to be derated for a continuous load, the question is, how much by?

 

This is why there are problems charging Lithiums with a standard alternator. The Lithiums will take all the alternator can output, but, the alternator will burn out very quickly running at 100% output

[Paul C]

5 minutes ago, magnetman said:

I think looking at the engine cooling system might be interesting. Undercooled engine is never a good idea specially with an older type. 

. 

 

The engine seems to be overcooled; or not being controlled properly with its cooling, than undercooled. My memory is vague but I'm sure on my previous boat, it had 2 circuits and 2 thermostats, it being a Beta thing.

[magnetman]

If the engine is producing enough power to fully load the alternator one does wonder if it is in fact getting hot enough to heat the calorifier. 

 

Maybe the answer is to have two calorifiers here. One for the lady and one for the gentleman.

 

Obviously the gentleman, assuming normal societal norms, will take the view that the ladies must be prioritised in terms of basic comforts and perhaps a system could be devised where one would share unequally the fruits of the diesel engine vis a vis the hot water. 

 

Strategic valve placement could enable the lady to disproportionately avail herself of the hot water. 

 

They do it all the time with money so why not the heated water? 

 

It could avoid considerable nuisance around argumentative behaviour.

3 minutes ago, Paul C said:

 

The engine seems to be overcooled; or not being controlled properly with its cooling, than undercooled. My memory is vague but I'm sure on my previous boat, it had 2 circuits and 2 thermostats, it being a Beta thing.

Of course I meant overcooled. The brain was thinking there was a problem and problems usually involve under-something rather than over-something.

 

 

 

[nicknorman]

1 hour ago, Alan de Enfield said:

 

It'll be a very expensive way of heating a calorifier full of water.

 

To Heat 1 litre of water by 10C = 105Wh (.105Kwh)

 

1 litre of water by 60 degrees = 105Wh x 6 = 630Wh 

 

So with your 600 watt heater it will take ~1 hour for each litre you want heating

 

If your engine uses 1 litre of diesel per hour (£1.50 ?) then it is going to cost you ~£1.50 per litre.

 

Assuming your calorifier is plumbed in to the engine circuit you will of course get heat from that, which will reduce the time you need to use the immersion heater.

 

 

Around a factor of 10 out old chap. Gross error check says that our 2kw electric kettle heats 2 litres of water from 10C to boiling in less than 5 minutes. 1 litre 2.5 mins. 1 litre at 600w about 7.5 mins. 1 litre at 600w by 60 deg about 5 mins.

 

 Being precise, specific heat of water is about 4184 joules per kg k. Or 1.16 Wh/kg k. So 600w is going to raise 1 litre by 60C in 7 mins.

 

We sometimes use our 1kw immersion from the batteries, and so far we haven’t turned into frogs nor been burnt at the stake for heresy. Although plenty have tried!

Edited April 9, 2023 by nicknorman

[casper ghost]

13 minutes ago, magnetman said:

 

Of course I meant overcooled. 

 

 

 

The engine is likely over cooled as there's no thermostat.

I could get a 1500w 240v heater and just run a Genny, especially if I plumbed the engine cooling back through the calorifier again. I do have a lever to direct the cooling water just through it and avoid the swim tank.

[magnetman]

10 minutes ago, nicknorman said:

So 600w is going to raise 1 litre by 60C in 7 mins.

 

 

 

So it is still going to take a long time to actually do anything to a ten gallon (45.4 litre) clorifier.