Strange Battery Monitor reading

[Gezzer]

I recently installed a BEP battery monitor, it reads everything ok until I press transmit on the VHF, then something strange happens /forums/images/graemlins/confused.gif

For instance this morning i was running the Eberspacher, cabin lights, fridge, nav, and stereo, reading about 7.5 amps discharge, nothing strange there, press transmit on VHF it reads 180 Amps CHARGE current, stop transmit all returns to normal.

I am thinking it is inductance from the VHF into the (shielded) battery monitor cabling, they are all within 6 inches of each other, any other ideas,

 

[alan]

Sounds like it is R.F. leakage, as you say, from your VHF cable into the battery monitor cable. It could be due to a poorly made connector on the coax cable at the radio or else it could be a poor grade of cable and it is leaking R.F.
I know from experience that the isolation of RG58 is not particularly good and that RG223 is much better.

You could try wrapping tin foil (bakofoil) around the VHF cable where the two cables are close together unless it is a long length then this is not practical. The best solution is to re-route one of the cables, keeping at least a metre of separation between them.

 

[markdj]

The shunt of the BEP monitor has two screws which they recommend using shielded cable to connect to so I'd check that first and if the cable is not shielded then get some microphone cable or similar and use that.

 

[CSFenwick]

[ QUOTE ]
For instance this morning i was running the Eberspacher, cabin lights, fridge, nav, and stereo, reading about 7.5 amps discharge, nothing strange there,

[/ QUOTE ]

Sounds pretty strange to me! If I was running that lot I'd expect at least double your 7.5 Amps. The Eber alone takes 7 Amps once it's chugging along (15-20A whilst firing up) and the fridge about 4A although that's not on all the time of course. No idea if this is connected to your problem but that reading sounds low to me.

 

[VicS]

If I was presented with this out of the blue I would very carefully check that the monitor was installed and connected to the shunt exactly as prescribed in the installation instructions, making sure the two twisted wires are connected to the terminals on the monitor and the shunt that they should be, that the screen was connected to the terminals it should be and that there was no interconnection between the screen and either of the twisted wires other than at the shunt.

Assuming that's OK I would be looking at how the power is supplied to the VHF. In days of olde it was usually recommended that the VHF was fed directly from the battery. With a battery monitor fitted that would mean connecting the negative to the opposite end of the shunt to the battery connection if its power use is to be monitored.

I would not like to comment on the RF radiation theory but I would have thought if it was a possibility there would be some warning in the monitor instructions about it. They do make a bit of point about the screen but as far as I can remember the BM1 supplied by Nasa and others does not require screened cable.

If the power to the radio can be disconnected close to it I would feel inclined to try a similar sized load connected in place of the radio. A car headlamp bulb perhaps. If that produces a similar odd effect then it's something wrong with the wiring but if it doesn't then OK it is an RF problem.