Been working on a 1950s Hotpoint dishwasher. This one came in missing parts of the gravity drain mechanism and with a bad water fill valve. I spent considerable time adapting a drain pump and installing a new water fill valve. I discovered it had an incorrect but working timer; and a spare timer. I spent quite a bit of time getting it working with the original timer, which failed with an open-circuit in the timer motor winding. The motor is soldered together and I was not able to get it apart to access the coil for any possible rewinding. The spare timer worked initially; then, while sitting unused that timer motor went open circuit as well.
This has been here for over a year and several have been looking for possible working timer motors. None have turned up and I need to get this project done. The Hotpoint manual shows the exact operation sequence of the timer. The dishwasher has four working parts that need to be controlled; the fill valve, drain pump, heater, and main motor. I got a 4-channel micro PLC to use to replace the timer. The Hotpoint manual shows the operation sequence of the timer, very clearly. I was able to write a program which emulates the mechanical timer; plus some enhancements based on what others have said were limitations on these dishwashers. The factory timer used a mechanism to break the cycle down into 45 second "clicks" of the timer cams. The contacts on the timer change state during the click from one step to the next. The PLC program emulates this by incrementing a cycle position counter every 45 seconds. The logic transitions the outputs of the PLC based on the position of the cycle, using information from the Hotpoint manual as a guide.
The original timer only had OFF and ON marked on the knob. You would manually advance the timer beyond OFF, and it would go through the cycle. There were no markings as to what part of the cycle were in effect at any knob position. Once the knob had rotated 360° back to OFF, the cycle ended. The PLC can't rotate the knob mechanically, so it instead uses a momentary switch. The original knob* is retained, but it is spring-loaded and can be turned to the right, making contact with a switch. When released, it springs back to OFF position. This signals the cycle to start. The same knob can be momentarily turned to signal the PLC to pause and restart, or to cancel the cycle and drain the water. In summary, the only external modification is that the knob does not rotate by its self during the cycle. *Note that the knob is not original to the dishwasher, because that was missing. The white knob is original to this project, but it would function the same even with the original Hotpoint knob in place.
I got it working, with very few outward modifications when the dishwasher is fully assembled. Hopefully this isn't considered a "horrible" thing to do to this dishwasher, but there was not really any other way at my disposal, to make this happen. In order to prevent the flood of comments asking this - the Micro810 module is a roughly $100 part, and the optional display attached to it is about another $60 but it is not necessary for this to function. Programming is written in a combination of function block and ladder logic.
By the way, there is a much earlier thread on this dishwasher, located here.
One of the limitations on this model was that it had two short wash cycles, with no way to add detergent between them. The later models had a detergent dispenser which allowed this to work and have detergent with each wash; but this model does not have this feature. I combined the two short wash cycles into one long wash, so that the detergent will be fully utilized. I also have an idea for a detergent dispenser which will shield the detergent from the initial fill and drain water spray, but allow it to be washed into the tub during the main wash cycle. I have an idea to test, which would keep water falling from above from the fill spray from hitting the detergent, but water spraying up from below from the impeller would be able to strike the detergent.
I have uploaded several still pictures here, and linked a YouTube video below.
Link for video, click this line of text!
Link for video, click this line of text!
Sincerely,
David
This has been here for over a year and several have been looking for possible working timer motors. None have turned up and I need to get this project done. The Hotpoint manual shows the exact operation sequence of the timer. The dishwasher has four working parts that need to be controlled; the fill valve, drain pump, heater, and main motor. I got a 4-channel micro PLC to use to replace the timer. The Hotpoint manual shows the operation sequence of the timer, very clearly. I was able to write a program which emulates the mechanical timer; plus some enhancements based on what others have said were limitations on these dishwashers. The factory timer used a mechanism to break the cycle down into 45 second "clicks" of the timer cams. The contacts on the timer change state during the click from one step to the next. The PLC program emulates this by incrementing a cycle position counter every 45 seconds. The logic transitions the outputs of the PLC based on the position of the cycle, using information from the Hotpoint manual as a guide.
The original timer only had OFF and ON marked on the knob. You would manually advance the timer beyond OFF, and it would go through the cycle. There were no markings as to what part of the cycle were in effect at any knob position. Once the knob had rotated 360° back to OFF, the cycle ended. The PLC can't rotate the knob mechanically, so it instead uses a momentary switch. The original knob* is retained, but it is spring-loaded and can be turned to the right, making contact with a switch. When released, it springs back to OFF position. This signals the cycle to start. The same knob can be momentarily turned to signal the PLC to pause and restart, or to cancel the cycle and drain the water. In summary, the only external modification is that the knob does not rotate by its self during the cycle. *Note that the knob is not original to the dishwasher, because that was missing. The white knob is original to this project, but it would function the same even with the original Hotpoint knob in place.
I got it working, with very few outward modifications when the dishwasher is fully assembled. Hopefully this isn't considered a "horrible" thing to do to this dishwasher, but there was not really any other way at my disposal, to make this happen. In order to prevent the flood of comments asking this - the Micro810 module is a roughly $100 part, and the optional display attached to it is about another $60 but it is not necessary for this to function. Programming is written in a combination of function block and ladder logic.
By the way, there is a much earlier thread on this dishwasher, located here.
One of the limitations on this model was that it had two short wash cycles, with no way to add detergent between them. The later models had a detergent dispenser which allowed this to work and have detergent with each wash; but this model does not have this feature. I combined the two short wash cycles into one long wash, so that the detergent will be fully utilized. I also have an idea for a detergent dispenser which will shield the detergent from the initial fill and drain water spray, but allow it to be washed into the tub during the main wash cycle. I have an idea to test, which would keep water falling from above from the fill spray from hitting the detergent, but water spraying up from below from the impeller would be able to strike the detergent.
I have uploaded several still pictures here, and linked a YouTube video below.
Link for video, click this line of text!
Link for video, click this line of text!
Sincerely,
David
