How much electric do i need !

Jody

Member
So how do I work this out.

Basically I have 12v Leisure battery and my current inverter is toast.

I want to be able to run....

Slow cooker when driving

Lap top (for a couple hours) when parked

12v TV when parked.

What is the calculation (once I've checked the power packs on each for ratings) for working out what size inverter I need. I figure the smaller (lower wattage) it is, the longer it will last off the battery but it's no good to me if it can't handle the slow cooker even when engine running.


Side note. Just before setting off on a 13 hour drive I prepped a chilli and stuck it in the slow cooker. 9 hours in I was able to stop for a lovely smelling warm chilli, and at my journeys end I was able to finish it. Thoroughly recommended.
 

d_bertko

Active member
Your stated needs are very simple.

Get a 12v car adapter for the laptop and charge it while driving. (Won't the laptop run off its battery for 4 hours on its own battery?)

Use a 12v slow cooker instead of your ac version.

Look at the tv power rating---you'd like twice the battery amp-hours than you'd use for your stationary needs.

Any other needs?

Plenty of advice available for a more extensive and complicated solution. But my general advice is either to go cheap or go expensive---too much compromise in the middle ground.

Dan
 
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autostaretx

Erratic Member
What i do for my laptops is buy a 12v to laptop adapter... instead of going up to 110vac and then back down to the laptop's ~18v

As for inverter ratings, it's good to have at least a 30% excess of inverter power.
If your slow cooker was rated at 700 watts, i'd go for a 1000 watt inverter.
Inverters are fairly efficient, so an excess rating doesn't cost much (in terms of battery drain).
Running an inverter at its full rating can lead to premature "toasting".

There are two common styles of inverter: "modified sine" and "sine wave".
The "modified" are (far) cheaper, but can damage/confuse various charger technologies (such as a power drill's charger) that you might plug into them.

That said, i fully agree with Dan Bertko: if you can get a 12v slow cooker: do so.

How many amp-hours is your leisure battery's rating?

--dick
 
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Midwestdrifter

Engineer In Residence
If you are only running the slow cooker when driving, I would try to get everything else running on 12V except the cooker. Then get an inverter which matches or exceeds your slow cookers watt rating. A 12v slow cooker is probably expensive, and I doubt it would be able to run from a standard 12v outlet due to the high current draw.

The TV and and laptops could be easily run for a day or two (of regular usage) from a aux battery in the 80-100AH range. But just working out the amp (or watt usage) of your 12v devices and converting to AH is a better method than just guessing. I would double whatver your AH needs are though.
 

jmoller99

Own a DAD ODB2 Unit.
1000 watt inverter running at full capacity will draw over 120 amps at 12 volts. I upgraded to a 150 amp alternator so i could run a 1000 watt sine wave inverter while i drove. 120 amps will suck a battery down very quickly, use it only when the engine is running.
 

autostaretx

Erratic Member
One slow cooker i have is only 200 watts, which would still be 200w/12v = 16 amps
... which would totally flatten a 67 amp-hour battery in 4 hours.

Your cooker may vary...
--dick
 

calbiker

Well-known member
You could toast the new inverter again. The 12V cables from inverter to battery need to be big.

You can probably get by with a 500W inverter.

Watching tv on only 1 battery is sketchy. It's best to monitor battery voltage and shut down power when battery gets to 12.1V.
 

Jody

Member
Right change of plan!!

the 12v fridge I currently have is rubbish so the plan is to replace it with an under counter fridge freezer than will be powered from the invertor when engine is running. When stopped with no power the firdge will have to gradually get warm but it's rare for me to stop more than 18 hours.
I have a built in charger so when I can plug in I will either run the charger from the mains OR figure a relay that'll auto switch the power when plugged in :)
 

Jody

Member
Right change of plan!!

the 12v fridge I currently have is rubbish so the plan is to replace it with an under counter fridge freezer than will be powered from the invertor when engine is running. When stopped with no power the firdge will have to gradually get warm but it's rare for me to stop more than 18 hours.
I have a built in charger so when I can plug in I will either run the charger from the mains OR figure a relay that'll auto switch the power when plugged in :)
 

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