Power Calculations

[OffGridManc]

Hi I need to work out my power needs and costs.

For example how do I work out how long 3 leisure batteries will run 250watts over x amount of hours and then how long I will need to charge that by a diesel generator.

Sorry if its been asked before.

[bottle]

Hi I need to work out my power needs and costs.

For example how do I work out how long 3 leisure batteries What size, will run 250watts Is that 240v AC or 12v Dc or 24vDC over x amount of hours and then how long I will need to charge that by a diesel generator. Generators do not charge batteries, chargers do, again what size and it will also need to be 'intelligent', ie, three stage charger.

Sorry if its been asked before.

 

See this thread:

 

http://www.canalworld.net/forums/index.php...mp;#entry485812

Edited February 5, 2010 by bottle

[barge sara]

Generators do not charge batteries.....

 

Unless its a DC generator like this

In which case they do.....

Edited February 5, 2010 by barge sara

[WotEver]

Unless its a DC generator like this

In which case they do.....

[pedant mode]

Strictly speaking, those are diesel powered chargers, not generators.

[/pedant mode]

 

Tony

[blackrose]

Has anyone who is good with Eccel knocked up a power audit spreadshhet that they wouldn't mind sharing?

 

Perhaps it could be pinned at the top of one of the forums (Living Afloat or Equipment?) as a useful feature.

Edited February 6, 2010 by blackrose

[Mat B]

Has anyone who is good with Eccel knocked up a power audit spreadshhet that they wouldn't mind sharing?

 

Perhaps it could be pinned at the top of one of the forums (Living Afloat or Equipment?) as a useful feature.

 

How's this?

 

Excell worksheet

 

m@

Edited February 7, 2010 by Mat B

[blackrose]

How's this?

 

Excell worksheet

 

m@

 

Thanks.

 

If I was being really fussy I'd say it could do with a separate column for mains appliances running off the inverter so I don't have to convert the figures

 

Just kidding. Actually I can read the power draw for everything straight off the battery monitor.

 

It's good thanks.

 

Mods: Could this spreadsheet be pinned please? The topic of power audits comes up again and again and this is an easy way to do it. Thanks

Edited February 8, 2010 by blackrose

[capnthommo]

Thanks.

 

If I was being really fussy I'd say it could do with a separate column for mains appliances running off the inverter so I don't have to convert the figures

 

Just kidding. Actually I can read the power draw for everything straight off the battery monitor.

 

It's good thanks.

 

Mods: Could this spreadsheet be pinned please? The topic of power audits comes up again and again and this is an easy way to do it. Thanks

i second the thanks.

i'm pants at spreadsheet design but i can use one so this is a real help. but i could use a pointer or two about what to do re the 240 running off inverter too. do i just use the figures for inverter running at it's continuous max or use the individual appliances? this leccy stuff is hard!

cheers

nigel

ps blackrose, thanks loads for the days cruise - really enjoyable - particularly as i'm not all that familiar with that end of the GU

[WotEver]

i could use a pointer or two about what to do re the 240 running off inverter too. do i just use the figures for inverter running at it's continuous max or use the individual appliances?

Use the power consumption that's stated at the back of the appliance on the boiler plate (in watts) and multiply that by 1.25. This allows a big safety margin for inverter efficiency - 80% - and they're nearly all better than that.

 

Then divide the answer by 12 to give you the current in amps.

 

eg - 250W appliance. Multiply by 1.25 to give you 312.5W. Divide by 12 to give you 26A. (Let's hope you don't have anything that big!)

 

Tony

[capnthommo]

Use the power consumption that's stated at the back of the appliance on the boiler plate (in watts) and multiply that by 1.25. This allows a big safety margin for inverter efficiency - 80% - and they're nearly all better than that.

 

Then divide the answer by 12 to give you the current in amps.

 

eg - 250W appliance. Multiply by 1.25 to give you 312.5W. Divide by 12 to give you 26A. (Let's hope you don't have anything that big!)

 

Tony

 

thanks for that - thats what i wanted

cheers

nigel