Power Consumption using a 12v 5 amp battery - Fiberglass RV


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Old 07-17-2017, 07:19 PM   #1
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Name: Peg
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Power Consumption using a 12v 5 amp battery

Calling on all amperage experts. I need help calculating power usage.

I have a small 12v, 5 amp battery that I charge at my camp site with a solar panel (13 watt). I use a Power on Board 400 watt inverter with it. The inverter has a no load draw of 0.3 amps.

I want to power a classic RCA Victrola 45rpm player (model 45-EY-2) which is rated at 50 watts. How long should I expect to provide music before the battery falls below 10 amps, which is when the inverter shuts down?

I also have a small electric fan, 23 watts, .35 amps. How can I calculate run time on this and other similar electrical components?

Peg
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Old 07-17-2017, 08:19 PM   #2
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Something just doesn't seem right here. If it's a 5 amp battery, then it's already below 10 amps. Do you mean 5 amp hours?

You shouldn't pull a battery below 50% of it's capacity. Doing so regularly will shorten battery life. On a 12 volt battery, that's 12.06 volts. Generally speaking, if you have a 5 amp hour battery, you shouldn't pull more than 2.5 amp hours from it.

Since you are using an inverter, which by the way will only give you 80% efficiency or thereabout, I'm assuming the player is 120 volts. to get watts to amps you divide the watts divided by the voltage; 50 watts/120 volts=.42 amps. So, 2.5 amp hours divided by .42 gives you about 5.9 hours, but remember there are losses in the inverter. At 80% inverter efficiency, that would give you 4.7 hours.

Is the fan 12 volts? If so, the wattage is probably the continuous draw and the amps list is the max amps on startup.

My I suggest that you go here: The 12volt Side of Life (Part 1)

It is a basic and good primer on 12 volt systems and will serve you well.

Are you powering an amp for the music as well, or does the player have an audio amp built in?

I am working from the information you provided. If the data I used is not correct, let us know.
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Old 07-17-2017, 08:21 PM   #3
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Watts=voltsxamps. Batteries
are rated as amp/hours and reserve cap. Or "rc" which is the number of minutes the battery will suppy 25 amps before dead. Add up your demand in watts x time of use in min.s and you have a start toward the answer.
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Old 07-18-2017, 05:48 AM   #4
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I meant to say that the inverter shuts off when the 12 volt battery falls to 10.6 volts. Sorry for the confusion.

The record player has its own amp. So that will save some juice!

Thanks for the math primer. It's very helpful information.

Peg


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Originally Posted by The Minimalist View Post
Something just doesn't seem right here. If it's a 5 amp battery, then it's already below 10 amps. Do you mean 5 amp hours?

You shouldn't pull a battery below 50% of it's capacity. Doing so regularly will shorten battery life. On a 12 volt battery, that's 12.06 volts. Generally speaking, if you have a 5 amp hour battery, you shouldn't pull more than 2.5 amp hours from it.

Since you are using an inverter, which by the way will only give you 80% efficiency or thereabout, I'm assuming the player is 120 volts. to get watts to amps you divide the watts divided by the voltage; 50 watts/120 volts=.42 amps. So, 2.5 amp hours divided by .42 gives you about 5.9 hours, but remember there are losses in the inverter. At 80% inverter efficiency, that would give you 4.7 hours.

Is the fan 12 volts? If so, the wattage is probably the continuous draw and the amps list is the max amps on startup.

My I suggest that you go here: The 12volt Side of Life (Part 1)

It is a basic and good primer on 12 volt systems and will serve you well.

Are you powering an amp for the music as well, or does the player have an audio amp built in?

I am working from the information you provided. If the data I used is not correct, let us know.
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Old 07-18-2017, 09:07 AM   #5
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Quote:
Originally Posted by The Minimalist View Post
Something just doesn't seem right here. If it's a 5 amp battery, then it's already below 10 amps. Do you mean 5 amp hours?

You shouldn't pull a battery below 50% of it's capacity. Doing so regularly will shorten battery life. On a 12 volt battery, that's 12.06 volts. Generally speaking, if you have a 5 amp hour battery, you shouldn't pull more than 2.5 amp hours from it.

Since you are using an inverter, which by the way will only give you 80% efficiency or thereabout, I'm assuming the player is 120 volts. to get watts to amps you divide the watts divided by the voltage; 50 watts/120 volts=.42 amps. So, 2.5 amp hours divided by .42 gives you about 5.9 hours, but remember there are losses in the inverter. At 80% inverter efficiency, that would give you 4.7 hours.

Is the fan 12 volts? If so, the wattage is probably the continuous draw and the amps list is the max amps on startup.

My I suggest that you go here: The 12volt Side of Life (Part 1)

It is a basic and good primer on 12 volt systems and will serve you well.

Are you powering an amp for the music as well, or does the player have an audio amp built in?

I am working from the information you provided. If the data I used is not correct, let us know.
While the player draws .42 amps at 120v, the input to the inverter is going to be around 10 times that. Wattage is the same, so if the voltage is less, the current must increase. 50 watts @ 12v is going to be around 4.2 amps plus any losses. A 5 amp hour battery is not going to power this very long. Amp hours are specified at a 20 hour rate, i.e. the battery load is such that the battery will last 20 hours before going dead. You are putting a heavier load than that; the actual amp hours will be considerably less than specified.

If you plan to run it more than a couple of minutes, I'd look for a larger battery.
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Old 07-18-2017, 09:52 AM   #6
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Originally Posted by Jon Vermilye View Post
While the player draws .42 amps at 120v, the input to the inverter is going to be around 10 times that. Wattage is the same, so if the voltage is less, the current must increase. 50 watts @ 12v is going to be around 4.2 amps plus any losses. A 5 amp hour battery is not going to power this very long. Amp hours are specified at a 20 hour rate, i.e. the battery load is such that the battery will last 20 hours before going dead. You are putting a heavier load than that; the actual amp hours will be considerably less than specified.

If you plan to run it more than a couple of minutes, I'd look for a larger battery.
Thanks John. Yeah, a failed to do the conversion to 12 volts. I shouldn't have had that second glass of wine.

Sorry to mislead you, Peg. At 4.2 amps, you might get a half an hour of good power, and probably less, as the faster you draw amperage from the battery, the less total amps can be drawn, and then there are losses from the inverter itself.

You never want to completely discharge a battery. The reason the inverter shuts off at 10.6 volts is that the battery is dead.

I'm with John. You need to get a bigger battery. I'd think at least a Group 24 deep cycle. That would give you about 80-85 amp hours, which at would give you about 8 hours or so before you reach the 50% charge level, allowing for losses in the inverter.
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Old 07-18-2017, 10:51 AM   #7
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Quote:
Originally Posted by The Minimalist View Post

You never want to completely discharge a battery. The reason the inverter shuts off at 10.6 volts is that the battery is dead.

I'm with John. You need to get a bigger battery. I'd think at least a Group 24 deep cycle. That would give you about 80-85 amp hours, which at would give you about 8 hours or so before you reach the 50% charge level, allowing for losses in the inverter.
It's tough planning an oldies sock hop while boondocking! So here's the plan: use the Group 24 battery (on board the Scamp) for the record player and use the smaller 5amp 12v battery for pink flamingo string lights. This is going to be a party! Thanks, all, for weighing in.
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Old 07-18-2017, 02:33 PM   #8
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A 5 amp per hour battery is almost like not having a battery if you plan to use any power at all. I would find someone that is qualified to help you size your battery bank and charging needs.
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Old 07-18-2017, 02:55 PM   #9
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Quote:
Originally Posted by herons View Post
I meant to say that the inverter shuts off when the 12 volt battery falls to 10.6 volts. Sorry for the confusion.

The record player has its own amp. So that will save some juice!

Thanks for the math primer. It's very helpful information.

Peg

The amp in the record play is Amplifier, amplifies electrical signals, takes power to do that. the Amp in current is Ampere a measure of current.
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Old 07-18-2017, 03:52 PM   #10
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Peg, sounds like a small generator would be the easiest fix.
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Old 07-18-2017, 04:19 PM   #11
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I have a AC fridge in my Boler (Fridge: 70W 0.8 Amp), a Motomaster Nautilus 24 AGM (79 AH) and a 40 W solar panel charger. I'm testing it today, here is the measured voltages:
Start: 12.92 V
2 hours later: 12.68 V
3 hours later: 12.51 V
5 hours later: 12.27 V (the solar panel was mostly under shade)
6 hours later: 12.45 V (the solar panel is under direct sunshine)
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