Battery Power

Hi Guys,
Can anyone tell me if my electrical calculations are correct.

I have a sleep apnea machine which _Affordable_Storage_Drawers.aspx 1amp at 240v does this mean it will draw 20amps at 12 volts using up a 160 AH battery in 8 hours.

It seems like a lot of power for a little motor.

(I realise I will lose 10% through the inverter and that I will need a 200AH battery to have 160AH on tap).

Thanks
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Reply By: Member - Serg (VIC) - Thursday, May 08, 2008 at 10:46

Thursday, May 08, 2008 at 10:46
Hi Jethro,

I bet that your apnea machine does not operate at 240V internally, but rather on some kind of DC voltage. So getting DC-DC converter in this case will be way more efficient. Your calculations correct for passive load (like tungsten bulb, iron or heater), but can be very deceptive with inductive one like motors. The best way is to hook-up inverter and measure amps directly.

Cheers
Serg
AnswerID: 302652

Reply By: Affordable Batteries & Radiators - Thursday, May 08, 2008 at 10:47

Thursday, May 08, 2008 at 10:47
No it would not draw 20A.

Have you got an inverter or a 12V adaptor for the unit ?

Regards

Derek.
AnswerID: 302653

Follow Up By: Jethro T - Thursday, May 08, 2008 at 12:46

Thursday, May 08, 2008 at 12:46
Thanks Derek,

I've heard of others using their machines so I thought my calculations might be a bit out or that 1amp would also include using the heater element in the machine which I don't use.

I have a 400/900w pure sine wave inverter, and a 90AH bettery which I might have to upgrade because I can't always use a generator.

Where can I cat a gauge to properly show how much power the machiune is drawing.
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FollowupID: 568775

Follow Up By: Affordable Batteries & Radiators - Thursday, May 08, 2008 at 13:30

Thursday, May 08, 2008 at 13:30
Only our NASA BM-1 will allow a load of 900W but it will show all the info you need.

Have you checked if a 12V adaptor is available for your machine ?
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FollowupID: 568782

Reply By: Affordable Batteries & Radiators - Thursday, May 08, 2008 at 10:49

Thursday, May 08, 2008 at 10:49
Here is a good file.

http://www.cpapaustralia.com.au/media_files/powering-with-batteries.pdf

Cpap-battery
AnswerID: 302654

Reply By: Member - Ken R (NSW) - Thursday, May 08, 2008 at 11:13

Thursday, May 08, 2008 at 11:13
I have a cpap machine and run the 12v through a cheap 100kw inverter and works fine. I'm not sure how many a hrs it uses but it doesn't appear to be a heavy user at all.
AnswerID: 302661

Follow Up By: Member - Matt (Perth-WA) - Thursday, May 08, 2008 at 11:52

Thursday, May 08, 2008 at 11:52
Ken you have a 100000W inverter??? Serious? Man I didnt think they came anywhere near that sort of output!!!
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FollowupID: 568766

Follow Up By: Member - Serg (VIC) - Thursday, May 08, 2008 at 12:25

Thursday, May 08, 2008 at 12:25
Furthermore – they came cheap!
:-))))))))
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FollowupID: 568770

Follow Up By: Jethro T - Thursday, May 08, 2008 at 12:51

Thursday, May 08, 2008 at 12:51
Thanks Ken,

Good to hear from someone in the same situation, I'm sleeping with the dingoes if I don't take the machine next time.

Can you get two nights use out of the one battery.

Regards
Jethro
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FollowupID: 568778

Reply By: Member - Olcoolone (S.A) - Thursday, May 08, 2008 at 12:12

Thursday, May 08, 2008 at 12:12
you can get inverters bigger then that....there called "power Stations".

Regards Richard
AnswerID: 302668

Follow Up By: Member - Ken R (NSW) - Thursday, May 08, 2008 at 12:45

Thursday, May 08, 2008 at 12:45
100 watt - sorry
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FollowupID: 568774

Reply By: Member - Ken R (NSW) - Thursday, May 08, 2008 at 16:56

Thursday, May 08, 2008 at 16:56
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This pretty much sums up the alternatives as i am aware.

Hope this works.

Kind regards and good luck

ken
AnswerID: 302721

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