converting shore kwh to battery amp hrs

[Paul C]

Quite possible immersion thermostat isn't being satisfied, result with 1kw immersion = 24 kwh per day

 

My back-of-envelope maths suggested that its on most/the majority of the time:

 

eg 168 hours in a week, 1kWh, usage was 100kWh/week

[ditchcrawler]

I'd say its plausible, given the calorifier was effectively heating the engine via thermosyphon effect so its going to be very inefficient/uninsulated as a system. The figures mean that the immersion element would have been on for most of the time.

 

I'd say:

 

1. Fit a one way valve to prevent this happening

2. "Double up" the insulation around the calorifier

3. Put the immersion heater on a timer, eg 1 1/2 hours in the early morning; 1 hour in the afternoon/evening if needs be. If there's going to be a greater need for hot water, override the timer to turn it on (but then turn it back to timer).

The one way valve will only work if the thermosyphon flow is the opposite way to which the engine pumps the water round

[Paul C]

The one way valve will only work if the thermosyphon flow is the opposite way to which the engine pumps the water round

 

True - so its worth getting this aspect 100% right. It might mean swapping the connections on the engine coolant coil of the calorifier.

[ditchcrawler]

 

True - so its worth getting this aspect 100% right. It might mean swapping the connections on the engine coolant coil of the calorifier.

And that alone may cure the problem

[Blazeaway]

Having read some articles on the net it seems that inserting a low lying loop in the feed hoses to and from the engine should stop the thermo syphon. Fyi currently hoses go from engine straight to the calorifier on a slight downward incline.

I've also bought a timer that I'll install.

 

So now back to the original post, eliminating the immersion I'm using 2 kwh per day.

 

Am I right that I will therefore need 2000÷10=200 amp hours from my battery bank ?

 

So what would be

1. ideal number of trojans T105's?

2. How many hours of 70 amp altetnator to put 200 amp hours back. Is it 200÷35 = 5.7 hrs ?

[Paul C]

A normal power consumption is typically in the range 50-150 Ah/day, so your 200Ah per day is high but not unbelievably so. Do you know approximately how it splits up? For example is there one item (possibly a heater of some kind, or a non-essential item) which could be met by gas use, or not needed while cruising?

 

If not then your maths is right.

 

The size of the battery bank is determined by: usable capacity, ie the range in between the lowest discharge you'd ever want and the state of charge once fully charged (which you'd hope to be 100% but pragmatically might fall a bit short of this). For example everyone recommends 50% State of charge (also 50% depth of discharge) and charging to 100%.

 

And the other measure is time between charging. Lets assume its a daily charge but obviously you could plan on every other day; or weekly.

 

So 200Ah/day, for daily charge from 50% to 100% would be met by a 400Ah battery bank.

 

Charge time - at the latter stages of charge, current is limited by the battery's acceptance of it, not how big the charger is - so it would take longer than your simple calculation. I'm not sure how much longer though......maybe someone else knows a formula?

 

Also bear in mind that for a proportion of the day the engine is running, during this the alternator should be able to supply the load at the time AND charge the battery (since it will have excess power most of the time....because the battery limits the charge, not the size of the alternator) so you only need to consider the power usage for when the engine isn't running, ie it might be 18 hours, and 150Ah. It might not be though because if cruising you probably (for example) don't watch telly at the same time. But you could maximise efficiency for (for example) charging laptops and phones while cruising.

[Iain_S]

 

True - so its worth getting this aspect 100% right. It might mean swapping the connections on the engine coolant coil of the calorifier.

 

Good idea; The engine's water pump will usually quie happily pump water "the wrong way" through a calorifier coil.

Might take a bit longer to heat the water from the engine, though, due to slightly reduced flow, and hottest part of the heating water hitting the coolest part of the calorifier first, and the hottest part when it's cooled down a bit.