Sola Ups 520 Fault

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OogieBoogie

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Aug 3, 2014
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Hello Folks,

I'm having issue with Sola Ups 520, with grounding. I'm trying to fault find, during the process I measured Voltage difference between the battery ground and chassis ground to be 8v. Does this sound normal? Is it not suppose to be near 0 volts not necessarily 0. Your opinion on this would be greatly appreciated.

I have looked through the PCB components and I cannot find any lead on how the voltage is leaking to chassis.


Thanks for your help :)
 
Solution
InvalidError
Depending on the UPS' design, there may be no direct connection between either battery terminal and ground... the low-voltage side could be almost fully isolated from the mains side except maybe for a MOV tying the low-voltage DC and high-voltage AC grounds together to prevent excessive float voltage.

So the 8V difference could be normal.
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Titan
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May 18, 2007
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Depending on the UPS' design, there may be no direct connection between either battery terminal and ground... the low-voltage side could be almost fully isolated from the mains side except maybe for a MOV tying the low-voltage DC and high-voltage AC grounds together to prevent excessive float voltage.

So the 8V difference could be normal.
 
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Solution
O

OogieBoogie

Reputable
Aug 3, 2014
2
0
4,510


If 8V is supposed to be there then, What seems puzzling to me is, there is a NPN transistor where base signal is provided by processor and collector is connected to fan with 24V and the emitter side is connected to chassis/AC ground. Whilst chassis Voltage aka emitter is more positive than base there is no current flowing, which the FAN never turns ON and This is part of the error the UPS is giving " FAN Fault", plus this ground is connected to other parts of the circuitry in PCB.

Also these two grounds 'DC ground to chassis' resistance measure to be roughly 15 - 17 kOhms, which seems reasonable i think.
I find it really hard to comprehend why this could be.
Any thought on this, why it could be designed this way?
 
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InvalidError

Titan
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May 18, 2007
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If your fan-control NPN connects to AC ground, that would be a violation of electrical safety regulations in most developed countries.

I tried measuring resistance between battery +/- and live/ground/neutral. They all read open as far as my DMM can tell.
 
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