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09-26-2012, 05:56 PM
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#1
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Member
Name: Ronnie
Trailer: 2000 Scamp 13, 72 Alpine Sprite
Alabama
Posts: 72
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Advice on using an inverter and Amp usage
I bought an inverter and it came in the mail today. I hooked an old style 13" TV, indoor antenna amp, and a digital converter to it. Testing the amps with everything running, it was right at 1 amp.
In about 30 minutes time I measured the voltage drop on the 12V battery and it went to 12.2 volts from about 12.4 at the start. It's a marine battery rated at 85 amp hours. Theoretically, shouldnt I be able to get 85 hours at 1 amp draw? Also, is it common for voltage to drop that fast?
I know I really need a true deep cycle battery, and I plan to install a solar panel one day, but for now I just need one nights television use on our upcoming boon dock trip. I have already installed LED lights.
Thanks for the help.
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09-26-2012, 07:29 PM
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#3
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Senior Member
Name: Eric
Trailer: Scamp 13
Michigan
Posts: 256
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Tom is asking the right questions. A few points.
Yes the 85 Amp hours theoretically means 1 Amp at battery voltage for 85 hours. Reality of course is different.
12.4 is not a fully charged good battery. Either your battery is getting a little old or it was not fully charged. I generally think of 12.4V as about 80% of full power. 12.2V as about 60% of full power. I would not go below 12V because these batteries do not like going way down as Tom pointed out. Personally, I try to stay above 12.2V
If you were running 1 Amp at 110V for a 1/2 hour that would roughly be 5 Amp hours at 12V (depending on the inefficiency of the inverter and wiring among other things). If your battery is many years old and/or has been cycled too often, and/or deep cycled too far down that would make some sense with what you are seeing (although it seems a little too fast going down for a good battery).
In addition to if the 1 Amp was on the 110 or 12V side, I would want to know everything that was hooked up to 12V and 110V and what was drawing power. If the 1 Amp was the TV and lights and other items were on that would explain why the battery voltage is going down faster.
I hope this helps. Let us know if you have questions.
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09-27-2012, 06:55 AM
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#4
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Member
Name: Ronnie
Trailer: 2000 Scamp 13, 72 Alpine Sprite
Alabama
Posts: 72
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Good question guys! Didnt think about the difference in which side I was getting the reading from. The 1 amp reading was on the 12v side going from the battery to the inverter as it was on and running those 3 devices I mentioned earlier.
The only other thing that runs on 12V in the camper is 2 LED lights, and they were off.
The battery is less than a year old.
I dont know how to take an amp reading on the 110 side. Is that where I should be reading?
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09-27-2012, 07:01 AM
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#5
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Senior Member
Trailer: No Trailer Yet
Posts: 5,112
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Quote:
Originally Posted by bicklebok
Good question guys! Didnt think about the difference in which side I was getting the reading from. The 1 amp reading was on the 12v side going from the battery to the inverter as it was on and running those 3 devices I mentioned earlier.
The only other thing that runs on 12V in the camper is 2 LED lights, and they were off.
The battery is less than a year old.
I dont know how to take an amp reading on the 110 side. Is that where I should be reading?
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What you are interested in is amp hours from the battery, so yes, reading amps from the battery is what you want.
1 amp to run all three of these devices at once is suspiciously low. Especially an older CRT television. After all, that is 12 volts times one amp = 12 watts - almost nothing.
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09-27-2012, 07:13 AM
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#6
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Member
Name: Ronnie
Trailer: 2000 Scamp 13, 72 Alpine Sprite
Alabama
Posts: 72
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Quote:
Originally Posted by ericw
Tom is asking the right questions. A few points.
If you were running 1 Amp at 110V for a 1/2 hour that would roughly be 5 Amp hours at 12V (depending on the inefficiency of the inverter and wiring among other things). If your battery is many years old and/or has been cycled too often, and/or deep cycled too far down that would make some sense with what you are seeing (although it seems a little too fast going down for a good battery).
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Can you explain this calculation for me please. Im still learning.
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09-27-2012, 07:18 AM
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#7
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Senior Member
Trailer: No Trailer Yet
Posts: 5,112
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Quote:
Originally Posted by bicklebok
Can you explain this calculation for me please. Im still learning.
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The power is proportionate on either side of the inverter, neglecting the inverter efficiency.
So, 1 amp at 110 volts is about 10 amps at 12 volts. So pulling 10 amps for 1/2 hour is about 5 amp hours of battery use.
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09-27-2012, 07:22 AM
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#8
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Senior Member
Name: Dave W
Trailer: Trillium 4500 - 1976, 1978, 1979, 1300 - 1977, and a 1973
Alberta
Posts: 6,926
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Volts x Amps = Power
12V x 1A = 12W
This gets more complicated on AC, but still basically applies.
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09-27-2012, 01:18 PM
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#9
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Member
Name: Ronnie
Trailer: 2000 Scamp 13, 72 Alpine Sprite
Alabama
Posts: 72
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I will top the battery back off with the charger when I get home, and then do another test.
Any suggestions on a good value true deep cycle battery? They are quite expensive!
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09-27-2012, 01:38 PM
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#10
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Senior Member
Name: Dave W
Trailer: Trillium 4500 - 1976, 1978, 1979, 1300 - 1977, and a 1973
Alberta
Posts: 6,926
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Quote:
Originally Posted by bicklebok
Any suggestions on a good value true deep cycle battery? They are quite expensive!
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Costco. I bought two group 24 batteries for about $75 each. The group 27 was about $99.
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09-27-2012, 01:48 PM
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#11
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Senior Member
Trailer: No Trailer Yet
Posts: 5,112
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Yea, Costco or Walmart both sell the so called Marine battery - not true deep cycle, but sort of a hybrid deep cycle / starting battery.
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09-27-2012, 06:04 PM
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#12
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Member
Name: Ronnie
Trailer: 2000 Scamp 13, 72 Alpine Sprite
Alabama
Posts: 72
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Thanks for all the help guys. Im actually using a marine battery now, but would like to get something better. I looked at the specs on my marine battery(cant remember them now) and it's actually pretty good.
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09-27-2012, 06:46 PM
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#13
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Senior Member
Name: Rene
Trailer: Bigfoot 2500 truck camper
British Columbia
Posts: 233
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I would try to figure out what your real loads are first before buying a new battery. Taking a voltage reading on the battery is only a rough guide to the batteries state of charge. Measure the amperage draw of the TV on 110v then measure the 12V current draw. Compare the two according to the formula David provided. Battery maintenance and operation are more important than battery brand or even type. Your battery is not that old unless it was badly abused by drawing it down until dead over and over. Use your head not your wallet.
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09-27-2012, 08:46 PM
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#14
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Senior Member
Trailer: Scamp
Posts: 7,056
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Quote:
Originally Posted by David Tilston
Volts x Amps = Power
12V x 1A = 12W
This gets more complicated on AC, but still basically applies.
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Same thing with AC. The key is power (Watts) stays the same.
120 Volts x 1 Amp = 120 Watts.
12 Volts x 10 Amp = 120 Watts.
__________________
Byron & Anne enjoying the everyday Saturday thing.
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09-28-2012, 06:49 AM
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#15
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Member
Name: Ronnie
Trailer: 2000 Scamp 13, 72 Alpine Sprite
Alabama
Posts: 72
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The battery I have now is in really good shape. It's less than a year old and has never been drained below 12 volts. I trickle charged it last night and it measured 12.9 volts this morning. I will measure it again this afternoon to see if it drops any after sitting all day. Then I will run the amp test with the appliances again.
I should have charged it all the way before I ran the test the first time but I was eager to try out the inverter!
Thank you again everyone for the advice!! I will report back after I hook everything back up this afternoon.
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09-28-2012, 07:02 AM
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#16
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Senior Member
Name: jim
Trailer: 2022 Escape19 pulled by 2014 Dodge Ram Hemi Sport
Pennsylvania
Posts: 6,710
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Just remember, with a 85 a/h battery you only have 34 a/h available to use, not 85. You maybe better off with a newer digital, led, 12v tv which would eliminate the inverter, box, and draw a lot less a/h.
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09-28-2012, 08:45 AM
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#17
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Member
Name: Ronnie
Trailer: 2000 Scamp 13, 72 Alpine Sprite
Alabama
Posts: 72
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Quote:
Originally Posted by cpaharley2008
Just remember, with a 85 a/h battery you only have 34 a/h available to use, not 85. You maybe better off with a newer digital, led, 12v tv which would eliminate the inverter, box, and draw a lot less a/h.
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Thanks. I will look into that. I think I saw another recent thread about 12v televisions.
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09-28-2012, 08:47 AM
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#18
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Senior Member
Trailer: No Trailer Yet
Posts: 5,112
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Quote:
Originally Posted by bicklebok
Thanks. I will look into that. I think I saw another recent thread about 12v televisions.
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Look for a TV that runs off a plug in wall transformer. If that transformer says -Output 12 volts DC - you are golden.
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09-28-2012, 08:50 AM
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#19
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Senior Member
Name: jim
Trailer: 2022 Escape19 pulled by 2014 Dodge Ram Hemi Sport
Pennsylvania
Posts: 6,710
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Here is the one I have, it works great...
JE1512LED - JENSEN 15" 12 Volt LED LCD TV
It has front controls, front speakers and draws 2 amps
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09-28-2012, 10:25 AM
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#20
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Senior Member
Name: Dave W
Trailer: Trillium 4500 - 1976, 1978, 1979, 1300 - 1977, and a 1973
Alberta
Posts: 6,926
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Quote:
Originally Posted by Byron Kinnaman
Same thing with AC. The key is power (Watts) stays the same.
120 Volts x 1 Amp = 120 Watts.
12 Volts x 10 Amp = 120 Watts.
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On AC you need to consider power factor as well. Power factor is the phase relationship between the voltage and the current. It is possible, with a purely capacitive load to have lots of voltage and current, but no power.
120 VAC x 1 A x 0.8 PF = 96 W
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