SSR switching capacitors

So I have the guts to a 10HP RPC I bought at an auction and integrated a lot of part into my larger RPC. The issue is that the potential relay they used is undersized and I would like to add a contactor to have it switch the capacitors indirectly.

I found I have no contactors that are suitable but I have a ton of 50A SSRs (Still have to check the capacitors to make sure they don't pass more than 50A), which would generally be no good for switching capacitors due to the massive surge load capacitors imply, but these only switch on when the voltage crosses 0, and only turn off when the current crosses 0. I can't think of any combination of on/off timing or capacitor voltage that could result in excessive voltage or surge current.


Does anybody see any issue with doing this? Biggest downside is I have to have low voltage control power, so the extra inconvenience may negate the convenience of having all parts on hand, but I figured even if I don't go through with it this way this might be an interesting topic for anyone who wants to switch out/in balancing capacitors in their RPC.

Is this to dynamically switch capacitors to optimize RPC output?

Tom

TDegenhart said:

Is this to dynamically switch capacitors to optimize RPC output?

Tom

Click to expand...

In this case it would just be to for starting. Really the only reason to use it for starting is because I already have the parts.

I'm still asking the question though because it would be really useful for dynamic balancing, even though that's not what I'm doing.

You can safety switch capacitors by putting current limiting resistor in series. As far as switching start to run, the caps should have a bleeder resistor across each one so startup is an non-issue. You are just breaking a circuit.

As to the potential relay, I use a simple mechanical timer to switch the start capacitors out.

Tom

Strostkovy said:

So I have the guts to a 10HP RPC I bought at an auction and integrated a lot of part into my larger RPC. The issue is that the potential relay they used is undersized and I would like to add a contactor to have it switch the capacitors indirectly.

I found I have no contactors that are suitable but I have a ton of 50A SSRs (Still have to check the capacitors to make sure they don't pass more than 50A), which would generally be no good for switching capacitors due to the massive surge load capacitors imply, but these only switch on when the voltage crosses 0, and only turn off when the current crosses 0. I can't think of any combination of on/off timing or capacitor voltage that could result in excessive voltage or surge current.


Does anybody see any issue with doing this? Biggest downside is I have to have low voltage control power, so the extra inconvenience may negate the convenience of having all parts on hand, but I figured even if I don't go through with it this way this might be an interesting topic for anyone who wants to switch out/in balancing capacitors in their RPC.

Click to expand...

I have rather a lot of similar goods, Crydoms exclusively, AC and DC, as I became "attached" to them, early 1970's as all-round problem-solvers.

But I'd not use them HERE.

My "project" the switching in/out of a 10 HP RPC and auxiliary as it is about to gain a 5 HP supplementary idler, rigged to run selectively as 5 HP, 10 HP, 15 HP. Common start cap as basically "don't much care", but the balance caps switched with the active idler(s), not shared when not selected.

The need? "Quartet" mill.

- 5 HP spindle + 3/4 HP knee power in Horizontal mode. No clutch. Tough start, more than a few of them, typical tasking.

- 1 3/4 HP spindle, 3/4 HP knee power in Vertical mode. No clutch, but easier starting.

Common juice pump off-machine, and single-phase, so not a factor. Minor load either way.

The other "consumer" a Kasto PHS, 2 HP or less.

5 HP RPC sometimes, etc. Each 10 HP Phase-Perfect "dedicated" (Cazeneuve 7 HP, Alzmetall 7 HP)

So...

I also have a stash of heavy-current capable Mercury-Displacement Contactors, 3PST 24V actuator coils. You can also find 120 V actuators, probably 220/230/240 as well.

Those are what I'd use where a single-throw was good-enough. (Up to) all three legs for power, ELSE one or two for power, third leg for a hold-in / "mag starter" function. Or wotever.

No external arcing. Perpetually renewed contact surfaces don't change characteristics, nor "wear out" anytime soon.

¡uʍop-ǝpᴉsdn ɯǝɥʇ unɹ ʇ,uop ʇsnſ