Need help with inverter

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System
System Posts: 2,511 admin
in Advanced Solar Electric Technical Forum #1
Web site seems to be very informed so hoping forum members can help or staff. I am just the ride along person in this auto but the other half isn't inclined to ask questions just try till it comes out right.
In a VW bus have 3 batteries. 1 auto for bus, one auto + 1 semi truck size just for lights, radio etc, wired separate and have dash cut off. Yes, I know 'a semi size?', the semi size has good charge and was not being used so bright idea-hook together for more capacity(?). Not my idea.
The 2 are charged while driving, shut off when sitting.
Installed Cobra 1500 continuous inverter. Properly hooked up etc., turned on shows 12.3 input. plug in laptop appears to work fine.
Plug in 1500W ceramic heater (has 2 settings) set on low, 10 seconds and inverter beeping that has Low input.
Plug in dremel works.
Am I just expecting too much to run the heater or is there a problem.
Thanks to all
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  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    #2
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    Re: Need help with inverter

    Welcome to the forum.

    You've actually answered your own question: Yes, you are expecting too much to run the heater.

    1500 Watts is the limit of the (probably MSW) inverter. At that point it is drawing roughly 125 Amps (or more - could be 150 as the battery goes down). Lots of loss in wiring there, and the net result is the inverter "sees" low battery Voltage at its input.

    Electricity is a very poor way to heat things. A Dremel draws almost nothing by comparison.

    I don't know what you're using to charge the inverter battery, but 12.3 Volts is a tad low. If you've got this wired in to your VW's electrical system your probably over-taxing the alternator, especially with the two other batteries. The mis-matched set, btw, is also a bad idea as they will not charge evenly. Nothing wrong with dual batteries, but they should be identical and the charging system must be able to handle the increased capacity.
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  • icarus
    icarus Solar Expert Posts: 5,436 ✭✭✭✭
    #3
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    Re: Need help with inverter

    The whole thing is simply a bad idea. Carting around an extra hundred pounds of battery is silly especially if you are going to use it for heat.

    Consider a Espar or Webasto heater instead.

    The ideal of charging a huge battery bank on the ~ 60 amp alternator in a VW is also crazy.

    Ceramic heater draws 1500 watts or~! 125 amps. Dremel probably draws under 50 watt or ~ 4 amp. No wonder you are getting low voltage shut down.

    T
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  • waynefromnscanada
    waynefromnscanada Solar Expert Posts: 3,009 ✭✭✭✭
    #4
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    Re: Need help with inverter

    There's just no way the average automotive alternator could ever begin to keep up with the load of such a heater. Sorry. How long would you expect to continuously crank the engine using the starter without running down the battery? The 1500 watt electric heater is basically the same thing, only it turns out heat instead of cranking the engine.
    You're definitely not alone in not realizing the heater is such a huge load on a 12 volt system, most people don't realize until they've tried it. But hey, it's a learning experience ;)
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  • BB.
    BB. Super Moderators, Administrators Posts: 33,440 admin
    #5
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    Re: Need help with inverter

    You will also find that a vehicle alternator is usually charging around 14.1-14.2 volts--Which will be around 10-20 amps for a mid sized battery.

    For every hour you run the heater, it would take ~5-10+ hours of running your van engine (1,200 watts / 12 volts = 100 amps; * 1 hours = 100 AH)

    You can get marine alternators that can be setup to charge at 14.5-14.8+ volts and really crank the amps into the battery--It still is better to not run a heater, or use a real genset and AC battery charger instead--Generally will save you a bunch of fuel and wear&tear on your vehicle engine.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
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  • vcallaway
    vcallaway Solar Expert Posts: 157 ✭✭✭✭✭
    #6
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    Re: Need help with inverter

    Also, your battery is probably not capable of kicking out 100+ Amps. I also suspect your severely under wired for that amperage.
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  • BB.
    BB. Super Moderators, Administrators Posts: 33,440 admin
    #7
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    Re: Need help with inverter

    Also, you should look at the Truck Battery and see if it an "automotive" style--Weighted to giving high starting currents (typically thinner plates and not liking going below 85% state of charge) or a Deep Cycle battery designed to go to 50% or even 20% state of charge.

    A deep cycle battery will last much longer than a "starter" type battery.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
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  • System2
    System2 Posts: 6,290 admin
    #8
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    Re: Need help with inverter

    thank you all for your help.
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