made a circuit using an dual opamp, its job is to increse current on a 0 to 10vdc circuit but maintian the incoming signal at the same level as the outgoing, the second opamp just switches a run and fail lamp. it works fine in testing using a resistive circuit but fails when attached to an EC motor 0 to 10vdc speed control signal. you can ramp the incoming signal up just fine and it runs OK but when the incoming signal is varied up and down a couple of times the output will not go above 1.8vdc, you can vary the signal from 0 to 1.8vdc but it will not go higher. once it has been turned off for a bit it will work again. it looks like some sort of interrnal over load kicks in. the output doer not rise above .1Ma

 

It would be helpful if you told us the part number for the opamp. Not many are able to source more than about 25mA.

 

sorry should have said, power supply is 15vdc opamp is LM358, it should handle 45ma but i checked the output whith a bench power supply and got 100uA max

 

LM358 are guaranteed to source 20mA (40mA typical), LM358A are guaranteed to source 10mA (20mA typical).

What are the relay coil resistances? I doubt that they're large enough for an LM358 to drive.

What is the component represented by a circle with an X in it?

Since you use wiring humps, are G and F connected?

 

sorry lm358, 20ma. relays are FRT4H 12vdc coil rated at .15watts. thie circle with X is a lamps which are LED,s. theyu are off the PCB , the letters next to small circles are pads to connect external components, square with numbers in are output terminals. i will disconnect relays and see if it works better

 

OK, this is odd. should have done this before. added probes to look at supply voltage. found when i try to use the circuit even with the LM358 pulled from its socket. thr power supply drops to 6 vdc. can not find a reason for any over load and the regulator does not get warm. the input power to the regulator can be as high as 35vac and i have to use a common ground.

 

finally found the problem, the 7815 was going low because the cheep 24vac output transformer was puting out over 38vac which is over the max voltage the 7815 was rated for.