bobxyz
Plastic
- Joined
- Mar 30, 2019
- Location
- Boulder CO
I've been having problems with blown start caps in a 10 year old RPC.
[Sorry in advance if this is too long of a post, I didn't want to miss anything important. I hope the pictures keep it more interesting. If you're bored, please skip to the questions at the end.]
Almost 10 years ago, I put together a 10HP RPC for my brother using an ebay kit, plus some upgraded parts and added caps for better balance. The RPC runs a woodworking shop with a 5HP table saw, a 5HP shaper, a bigger 9HP saw, plus a couple other similar machines. Mostly one machine at a time.
For the last 9 1/2 years, it's been working fine with zero maintenance. A few months ago, a surplus 5HP dust collector (high starting load) was added and it didn't want to run right. Within maybe 15 minutes?, one of the start caps (200uF 220VAC) smoked.
At the time, it was setup with (see above picture for details):
- Start caps: 900uF total
- Primary Run caps: 240uF total
- Seconary Run caps: 102uF total
- PFC: 25uF total
The original set of 3x 200uF 220VAC start caps, or should I say 2x caps and one blown cap, was swapped for new higher voltage surplus 200uF 330VAC start caps, and the RPC was working again, but without trying to use the new 5HP dust collector. This lasted a couple months and then another start cap blew, this time, a 100uF 330VAC one that had been in use for 10 years. When it blew, the RPC had been on for ~10 minutes and table saw was cutting 1/4" ply, so not a big load.
The remaining original 3x 100uF 330VAC start caps were then replaced with a couple more new surplus 200uF 330VAC start caps, giving 5x 200uF or ~1000uF of total start capacitance (a bit high for a 10HP idler, but I wanted a fast startup to help eliminate issues). It's all running again but I'm worried that the potential relay is occasionally sticking and causing the start caps to blow up.
The measured voltages VAC are (L3 is generated leg):
Here's oscilloscope graphs of the current setup running just the idler motor and running the 5HP table saw with the power feeder on high rate (but soft wood). Seems reasonable to me, but I'm far from a RPC expert. Note: L1,L2 (blue,magenta) are 50V/div scale while L3 (green) is 100V/div scale.
The potential relay is mis-mounted with "This Side Up" to the left.
I couldn't find an original datasheet for the White Rodgers #128306-2965AB potential relay, but one of the surplus sites listed it as:
PICK-UP:245-275V. DROP-OUT:140V CONTINUOUS
COIL VOLTAGE: 420V. 10,000 OHMS NOM.
RESISTANCE 5-VA NOMINAL; 10 VA INRUSH
Oh, and here's a graph of the generated leg at initial startup (10HP idler). Mighty fast, and maybe too fast?
Questions:
1) How often do potential relays "stick"?
2) Will mounting the potential relay in the wrong orientation cause it to "stick"?
3) How do I select a replacement potential relay? Is there something I can measure when trying to start the problematic dust collector to help select good pick-up and drop-out voltages?
4) If the potential relay "sticks", how long until the start capacitors blow? Seconds? Minutes? Hours?
5) Does anything seem off in the RPC setup or measurements?
Thanks,
Bob
[Sorry in advance if this is too long of a post, I didn't want to miss anything important. I hope the pictures keep it more interesting. If you're bored, please skip to the questions at the end.]
Almost 10 years ago, I put together a 10HP RPC for my brother using an ebay kit, plus some upgraded parts and added caps for better balance. The RPC runs a woodworking shop with a 5HP table saw, a 5HP shaper, a bigger 9HP saw, plus a couple other similar machines. Mostly one machine at a time.
For the last 9 1/2 years, it's been working fine with zero maintenance. A few months ago, a surplus 5HP dust collector (high starting load) was added and it didn't want to run right. Within maybe 15 minutes?, one of the start caps (200uF 220VAC) smoked.
At the time, it was setup with (see above picture for details):
- Start caps: 900uF total
- Primary Run caps: 240uF total
- Seconary Run caps: 102uF total
- PFC: 25uF total
The original set of 3x 200uF 220VAC start caps, or should I say 2x caps and one blown cap, was swapped for new higher voltage surplus 200uF 330VAC start caps, and the RPC was working again, but without trying to use the new 5HP dust collector. This lasted a couple months and then another start cap blew, this time, a 100uF 330VAC one that had been in use for 10 years. When it blew, the RPC had been on for ~10 minutes and table saw was cutting 1/4" ply, so not a big load.
The remaining original 3x 100uF 330VAC start caps were then replaced with a couple more new surplus 200uF 330VAC start caps, giving 5x 200uF or ~1000uF of total start capacitance (a bit high for a 10HP idler, but I wanted a fast startup to help eliminate issues). It's all running again but I'm worried that the potential relay is occasionally sticking and causing the start caps to blow up.
The measured voltages VAC are (L3 is generated leg):
L1-L2 | L1-L3 | L2-L3 | |
Idler Only | 242.9 | 255.1 | 254.6 |
Idler + Idle Table Saw | 242.2 | 246.8 | 244.4 |
Idler + Sawing w/ fast feeder | 240 | 239 | 243 |
Here's oscilloscope graphs of the current setup running just the idler motor and running the 5HP table saw with the power feeder on high rate (but soft wood). Seems reasonable to me, but I'm far from a RPC expert. Note: L1,L2 (blue,magenta) are 50V/div scale while L3 (green) is 100V/div scale.
The potential relay is mis-mounted with "This Side Up" to the left.
I couldn't find an original datasheet for the White Rodgers #128306-2965AB potential relay, but one of the surplus sites listed it as:
PICK-UP:245-275V. DROP-OUT:140V CONTINUOUS
COIL VOLTAGE: 420V. 10,000 OHMS NOM.
RESISTANCE 5-VA NOMINAL; 10 VA INRUSH
Oh, and here's a graph of the generated leg at initial startup (10HP idler). Mighty fast, and maybe too fast?
Questions:
1) How often do potential relays "stick"?
2) Will mounting the potential relay in the wrong orientation cause it to "stick"?
3) How do I select a replacement potential relay? Is there something I can measure when trying to start the problematic dust collector to help select good pick-up and drop-out voltages?
4) If the potential relay "sticks", how long until the start capacitors blow? Seconds? Minutes? Hours?
5) Does anything seem off in the RPC setup or measurements?
Thanks,
Bob