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SCR Rectifier Dayton Speed Control Need cross reference No one can find


Guest TheButcher69

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Guest TheButcher69

I have a Dayton 5amp Speed Control that the Rectifier shorted between the cathode & anode. The part # is: 66497 RCA Date code C-7613. I've called & searched everywhere & no one has any info. I've tried to replace it with: "S8040R-ND" & "S4010LS2-ND" but on variable speed the motor just hums. Any help would be appreciate! Here are some pictures.

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Guest TheButcher69

No I'm not sure at all. I was just going by a Digikey rep. & Dayton/Grainger rep said about it not being a triac but I'm having second thoughts that these guys are wrong because on another forum someone said the same thing as you & I tried 2 SCR's both did the same thing. The other person on the other forum suggested doubling the voltage & going off of the motor draw & try a random triac & will be using this on different motors such as a bench grinder dremmel ect.

I'm in the USA so voltage would be 110v & the circuit is rated for 5amp so I was thinking anything at 240v to 400v & atleast 10amps in a triac. Would my thoughts be correct?

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Guest TheButcher69

The unit plugs into a 110 outlet & then any 110 device plugs into it. There is a rocker switch "Off" in the middle" right "Full" speed left "Variable"

On the inside there is a 1k 1/2 watt resistor attach to the switch which runs to the "cathode" & attaches to the "Gate" a "Diode" then connect to the "Gate" & runs to the "Wiper" on the pot. The right end of the pot connects other "Diode" & runs to the top pots "Wiper" & finally the top pots right end connects the "Neutral" AC wires that run from the cord of the unit & runs to the receptacle of the unit. The "Black" wires run to the switch & the fuse & receptacle.

There is another 4k resistor that runs from the switch to the "anode" & then runs to the pots left end

Here is a picture of the outside & inside of the unit.

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Guest TheButcher69

I'm really not sure it's not a triac. I'm only going by digi-key rep & a guy on youtube. They said the K A G represent an SCR. I have limited knowledge. I know a triac is basically 2 SCR's put together that allow current to flow each way. But I don't know how to test for a bad one. I know I had resistances between the cathode & gate & a short between the cathode & anode & I think there was resistance between the anode & gate but I can't say for sure I'd had to retest it.

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Yes K, A G does normally mean SCR.

But the socket seems to indicate it uses the whole waveform and there are only two diodes, rather than the four expected in a full wave rectifier.

You really should try to draw the schematic, even if you're not sure of the components. Just draw the TRIAC/SCR as a box with the pins numbered from left to right (front view).

Another thing you could do is consider stripping out the original circuit and replacing it entirely with a standard phase controller circuit.

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Guest TheButcher69

I REALLY appreciate your help! But when it comes to schematics I'm really lost. I'm a machinist by trade & have no troubles reading them but electrical is a bit beyond me. I'll have to do research on the standard phase controller circuit too.

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