Protecting transistors in mult-winding multi-transistor systems

[radiant]

Hi

Just thought I'd share some thoughts about making these systems more rugged.

My setup at the moment is running from 48V @ 7.3A into 20 circuits each with doubled up 23AWG wire each (total 41 wires litzed) 2.5ohm DC
resistance each circuit....

Insane charging capability I know....but from time to time, one or two neons will explode and short out CE of the
transistor it was on....causing my solar breakers to trip.

So far I have a circuit breaker on the input to limit current draw to 10A and trip in event a short occurs....
I have also removed the neons now as they were causing more grief than benefit in my setup which has the charging batteries
connected permanently....so no risk of disconnection.

Now, I have tried adding a ballast resistor to each neon in an attempt to save the neon from death, however , the
neons started glowing way before non-resistored ones used to....interesting!

Glowing neons = radiant not going to battery! Can't have that.

What advice beyond overcurrent protection and neons is there for the protection of transistors?

[ZeusZcid]

Do you mean that the neon glow while the setup is connected to a charge source or only when disconnected?? At 48V you probably need to run two or three neons in series to handle the higher voltage spikes. Most neons are only 90V to 110V unless you have higher rated ones.

[radiant]

Yes it glows while the charge bank is connected....but only when a ballasted (series resistor) neon is used....I dare not run the system without a charge
battery connected!!!! That would be instant death to one or more transistors.

Interesting idea, series the neons across each transistor....

Anyone have any ideas about using TVS diodes across the CE of each transistor?

[radiant]

OK problem solved! A 200V bi-directional TVS diode on the output. Trips the breaker perfectly before any transistor damage...and not a neon in sight...

[Tom C]

Hi

Just thought I'd share some thoughts about making these systems more rugged.

My setup at the moment is running from 48V @ 7.3A into 20 circuits each with doubled up 23AWG wire each (total 41 wires litzed) 2.5ohm DC
resistance each circuit....

Insane charging capability I know....but from time to time, one or two neons will explode and short out CE of the
transistor it was on....causing my solar breakers to trip.

So far I have a circuit breaker on the input to limit current draw to 10A and trip in event a short occurs....
I have also removed the neons now as they were causing more grief than benefit in my setup which has the charging batteries
connected permanently....so no risk of disconnection.

Now, I have tried adding a ballast resistor to each neon in an attempt to save the neon from death, however , the
neons started glowing way before non-resistored ones used to....interesting!

Glowing neons = radiant not going to battery! Can't have that.

What advice beyond overcurrent protection and neons is there for the protection of transistors?

IF your neons light up AND everything is working correctly, then the spike is NOT being absorbed by the battery, regardless of the protection, it will be lost as heat somewhere, most likely in those diodes. your charge batteries are either full or just too small or too sulphateed to absorb the spike.

at 12 volts you can get a spike above 200 easily at 1 amp draw, higher draws at 12 volts produce spikes above 700 volts. 7.3 amps at 48 volts primary is somewhere around 30 amps at 12 volts, you have built a brute force pulse charger.

what size batterie are you trying to charge, anything smaller than a forklift battery is too small. your current is just way too hi! even JB's 24 volt rejuvenator never pulls more than 8 amps.

current kills radiant.

pictures please

Tom C