Forum Discussion

Passme's avatar
Passme
Explorer
Apr 18, 2017

Converter power requirements

They say a little information is a dangerous thing so I'm throwing this out there for confirmation/correction, I thank you in advance.
Bought a 1500 watt inverter and figured I could wire it into the control panel 12V feeder leads coming from the battery. Two ft of supplied wire (included in the purchase) and I'm ready to rock
Then I stumbled upon a few rules! AC watts ÷ 10 = DC watts. Is this true? If I demand 5 Amps AC from converter it will draw: Amps(AC) x Volts=Watts, so 5x110=550 Watts. Now the bad news: watts(550)÷10=55 Amps DC. 55 Watts! Is this true? No wonder it suggests you use the heaviest gauge wire run the shortest distance.
My 206 Ahr rated batteries would be ruined in 4 hrs, at 1/3 draw down (suggested to max out battery life) I can power a 5 amp appliance for 1hr, then its fire up the generator and recharge the batteries. If this is accurate I'm returning that 5100 watt inverter or upgrading to 450+ Ahr battery capacity. Even then I might get 2-3 hrs.
I'm considering a 400 watt inverter to power my 3 amp draw LED tv for 2-3 hrs of viewing between charges.
I kinda hope someone tells me this is wrong, I can power the average campground by plugging my inverter at the gate.
Any and all feedback is greatly appreciated.
  • jwandvassie's avatar
    jwandvassie
    Explorer
    Apr 18, 2017
    KD4UPL wrote:
    Watts are watts, AC or DC doesn't matter. The amps change with the voltage. A 1500 watt load at 120v will draw 1500/120 = 12.5 A. BUT, the inverter isn't supplying the power, the battery is, and it's at 12v. So, to supply 1,500 watts from your 12v battery the inverter is drawing 1500/12 = 125 amps. Really, it will be a bit higher because inverters are not 100% efficient. That's why most people just divide the watts by 10 to get a rough idea of the amps from the 12v battery.
    So, yes, if you want to power a 1,500 watt in


    ^^^^Perfect Answer^^^^^
  • Passme's avatar
    Passme
    Explorer
    Apr 18, 2017
    Thanks everyone, and I apologize for the numerous numerical and reference mistakes in my post. Gotta review it before posting. The "watts is watts" reply turned on the light bulb (pun intended) for understanding this massive amp draw when sourcing DC for an AC load. My batteries: 2 Interstate PowerFast Series 6V, PF-GC2-UTL. 107@75A, Ahr 208. Not sure what the 107@75A refers to but yes I have 208 Ahr to play with. So to protect batteries I should draw 1/3 then recharge. 208x.33=68 Ahr. My furnace draws around 10 amps so I can run it 6-7 hrs then it's recharge time. Is this correct understanding of my DC RV power?
    My batteries as they stand will support my LED tv plugged into a 400 watt inverter for 2-3 hrs a nite, then recharge em with generator while brewing that all important pot of morning coffee. Final question if I may, I have a WF-9855 converter onboard, if I limit all RV draws how long would it take to recharge the battery bank with the 55 amp converter output? Thanks everyone who posted, learning so much from you folks!
  • independent_TJ's avatar
    independent_TJ
    Explorer
    Apr 18, 2017
    Bobbo wrote:
    independent_TJ wrote:
    You said "206 ah batterIES" (plural). If your converter is drawing 55amp/hr (aka 550wh @ 10vdc since you used 10v in your post),....then that is being drawn from the total amp/hr of your total battery BANK. If you have 2x 206 amp/hr batteries, then your battery BANK is 412 amp/hr of stored power.

    Unless they are 6v batteries in series, then your amp/hr truly is still 206.


    indeed. I just wanted to be sure the OP is using the TOTAL amp/hr of the TOTAL battery bank. :) I have a minor solar setup as backup power for my home so I have learned: "if you want longer source of battery, you have to have more amp/hrs in your bank....so get more batteries or only use the appliances WHILE the sun is recharging what I am using."
  • Bobbo's avatar
    Bobbo
    Explorer II
    Apr 18, 2017
    independent_TJ wrote:
    You said "206 ah batterIES" (plural). If your converter is drawing 55amp/hr (aka 550wh @ 10vdc since you used 10v in your post),....then that is being drawn from the total amp/hr of your total battery BANK. If you have 2x 206 amp/hr batteries, then your battery BANK is 412 amp/hr of stored power.

    Unless they are 6v batteries in series, then your amp/hr truly is still 206.
  • independent_TJ's avatar
    independent_TJ
    Explorer
    Apr 18, 2017
    Also, as you may have already figured out...a 1500w power inverter should have ALL supply wiring large enough to handle the max DC amp-draw of the inverter....so wiring it to the battery leads of the 12v charger might not be sufficient for the DRAW. That wiring between the charger and the battery is usually smaller because it is used for a lower current.
  • independent_TJ's avatar
    independent_TJ
    Explorer
    Apr 18, 2017
    You said "206 ah batterIES" (plural). If your converter is drawing 55amp/hr (aka 550wh @ 10vdc since you used 10v in your post),....then that is being drawn from the total amp/hr of your total battery BANK. If you have 2x 206 amp/hr batteries, then your battery BANK is 412 amp/hr of stored power.
  • 2oldman's avatar
    2oldman
    Explorer II
    Apr 18, 2017
    It's not wrong. Tell us why you bought a 1500w inverter in the first place.
  • KD4UPL's avatar
    KD4UPL
    Explorer
    Apr 18, 2017
    Watts are watts, AC or DC doesn't matter. The amps change with the voltage. A 1500 watt load at 120v will draw 1500/120 = 12.5 A. BUT, the inverter isn't supplying the power, the battery is, and it's at 12v. So, to supply 1,500 watts from your 12v battery the inverter is drawing 1500/12 = 125 amps. Really, it will be a bit higher because inverters are not 100% efficient. That's why most people just divide the watts by 10 to get a rough idea of the amps from the 12v battery.
    So, yes, if you want to power a 1,500 watt in

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