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Inverter/Charger has high voltage at battery terminals?

edited December 2014 in Renewable Energy
I've got a new 12V->220V inverter/charger and it works fine, but I've noticed that whilst its chassis/cabinet is earthed, there is a potential difference of over 100V between either battery terminal and earth.

Is this normal?

Comments

  • It could be that the battery and immediately associated electronics is completely isolated from the AC side and is just “floating” to such a voltage but that there's a very high impedance behind it. I'm imagining capacitive coupling through the transformer so that the DC side is floating to half the AC voltage.

    Try bridging from one of the battery terminals to earth with something like a 470k ohm resistor. Even if there's a full 200 V across it that'll only draw a tiny current and dissipate negligible power but I expect it'll actually drop the voltage quite a lot.
  • Thanks Ed, that sounds like a good thing to try. I was wondering if there was a"half of mains" volts relationship.

    Not having a 470k to hand, would it possibly hurt the inverter if I used a 60W incandescent light bulb?

    Of course, the thing I'm more concerned about is if it would hurt a person - who happened to be touching the chassis whilst they touched a battery lead (with the unit operating).
  • Make and model of inverter? What does the maker say about it?
  • Connecting a bulb across like that really _ought_ not to do any harm but using a higher resistance would be a bit more conservative. An incandescent bulb has a pretty low resistance when it's first turned on; the resistance increases as it heats up. That's why they turn on so quickly. [¹] [²]

    Trying to think of a purely resistive low-power mains device. Difficult. Small soldering iron?


    [¹] It's also something all (ex-)HP employees ought to understand - the company got started making an oscillator which used the positive temperature coefficient of a light bulb for stabilization. A few used in the making of the film Fantasia.

    [²] Also, I think, why they tend to blow when you turn them on.
  • Here's a link to details of it: http://www.voltpolska.pl/produkty/przetwornice-dcac-sinuspro/sinuspro-1000w-12v-230v-7001000w.html

    I have a soldering iron, I'll see what its resistance is, ta.
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