Grounding Cable Sheild

[laingalion]

I have a project which is powered by a 40 V lithium battery. I then use an H-Bridge to turn it into an AC signal to feed a transformer (at around 20 kHz). The transformer steps up the voltage to around 2 kV to power a transducer. It draws a lot of power, approximately 1 kW RMS.

I used a thick shielded cable (maybe 10 ft) from the transformer to the transducer. To where should I bond the cable shield? Should I bond it to the negative terminal of the battery? Should I let it just float? I imagine bonding it to one of the legs of the transformer would defeat the purpose of the shield.

I did a search on the forums and see that bonding to the DC ground is best, but in my case the shield is after a transformer and I am worried about noise being fed back to the circuit. The control side is also powered by the same battery.

Side concern: I am also really worried about interference to the low voltage (5 V) control side. Even though I put in a ground plain, avoided circuit loops, and put capacitors near every chip, I am worried about the 25 amps flowing across the H-Bridge. I have actually built the system and it works fine but it still worries me. Any suggestions or best practices would be very welcome.

[Rerouter]

Te idea of a shielded cable is to prevent external interference from entering your circuit, as such should be tied to the lowest impedance return in your case the negative of the battery, and right at that terminal, if you tie it in with the ground that is supplying your inverter, even though its a high discharge lithium you will have some fluctuation in voltage which can turn your shield into an antenna.

[laingalion]

Te idea of a shielded cable is to prevent external interference from entering your circuit, as such should be tied to the lowest impedance return in your case the negative of the battery, and right at that terminal, if you tie it in with the ground that is supplying your inverter, even though its a high discharge lithium you will have some fluctuation in voltage which can turn your shield into an antenna.

Thanks very much for the reply.

The negative terminal of the battery is the same as the ground supplying the inverter. I am designing this incorrectly? Am I missing a fundamental step? The battery terminal is only a few inches of conductor away from the inverter. I tried to make it as short as possible to reduce any noise.