Leisure Battery for Inverter

[BillyBB]

Please check my maths on this. Want to fit a 2000w inverter on a deep cycle battery with split charge relay. Ignoring the 90% efficiency to get 200w out at 230vac I need to put 2000w in at 12vdc, that works out at 167amps.
Do I need a 170amph rated battery to supply this? They weigh more than my generator!
Are those folks who use 100amp batteries on this sort of set up just starving their inverter?

TIA

[BillyBB]

Ooops to get 2000w out I need to put 2000w in

[rccatnap]

Why not give these people a call tomorrow?
http://www.caravantec...om/2000WInverter.aspx

[beso]

Storage battery capacities are rated in AmpHours. This is the energy capacity. Usually set at 10 hours a 170 Ah battery will provide 17 amps for ten hours.

At higher currents the capacity of any battery reduces. Pulling 170 Amps for an inverter will result in a very short run time much less than an hour.

Home lighting batteries are usally rated at 100 hours so be sure understand the rating applied when deciding on the batttery. Also you should not regularly severely discharge a batter as it shortens their life. Below fifty percent the number of discharge cycles drops very rapidly. Long life requires discharging only ten to twenty percent of the full capacity.

Note that your inverter will not pull 167 amps to run a 100 watt load. However an overly large inverter will be less efficient on a small load.

If you are running a large appliance you will need to run the vehicles charging system. These can typically supply 50 amps or more on an idle depending on the vehicle.

Car batteries are rated at Cold Cranking Amps (CCA). This is the maximum current they will supply to a starter motor. They don't do this amperage for very long and the relationship to the energy capacity is not defined.

[BillyBB]

Thanks. I'm probably going to choose a smaller inverter and take the genny for heavier days.
To do what I want I would need a battery bank, 50amp charging is not enough. Don't want to kill the alternator.

[regulo]

Not sure your calculations are right here.

For ease of thought assume 200W at 240v. Current required I =W/V, which gives 0.83Amps. On the input side at 12v you will need 240/12 x 0.83 roughly 16.7 Amps.
All excluding losses and inefficiencies, and not strictly accurate. Still a huge draw on a 110 A/hr battery, and only likely to give you a couple of hours useful capacity. As well as knackering your battery in pretty short order!

[BillyBB]

2000 not 200 see my first reply

so 167 not 16.7

actual rating of drill is 1200W so load would 'only' be 100amp at 12v (and 100% efficiency)

don't fancy boiling sulphuric acid in my van

so not worth doing when I already have a lovely 2.5Kva genny, perhaps I'll put wheels on her.

thanks all

[regulo]

Oops, sorry BillyBB, missed that.

In that case, you are right. Keep that genny running sweet!! I jumped in quick 'cos I know folks use their laptops thru inverters on their boats, and can get away with a good 3 hours from a 110A/Hr battery.

Regards, Ray.