Mechanical Relay Quality

[evilkitty]

Re: Mechanical Relay Quality

Post #6 says you measured "0.67A up to 1A then back down" and now you're saying 32mA ???

I looked at Heil ICP Tempstar PA5536AKA4/PYPA36GA4 heat pump, from your picture. It looks just like an air conditioner but has a reversing valve to pump heat into the home and there's some optional electric heater package.
Power transformer is 24VAC 40VA. Based on pictures, you can figure out the schematic of the Heil control board 1087562/Honeywell 1084-83-100A, if I'm right about the one in your outdoor unit.
The thermostat inputs are low current going to a PIC MCU. There is no usual 24VAC inductive loads the thermostat relays would be seeing, like contactors etc.
So either your wiring is wrong and you are crowbarring something or this is a massive goosechase due to a cheap crappy Songle relay.

i did not use a clamp meter this time, i used a meter that measures the current flowing through the meter with wires

"goosechase due to a cheap crappy Songle relay" is what i have been thinking

the only changes i did on the AC side was moving the wires for the tubes to the relays in the thermostat
https://www.badcaps.net/forum/newrep...eply&p=1105511
I do not think i have a way to measure that

Does this unit have a time delay for the fan to go off when the temperature hits the set point if does they quite often fail open which means they do not turn on the fan or the fan never turn off in auto fan control mode

the fan does have a delay as far as i know, the fan does turn on/off in auto mode

Digital inputs to HVAC (furnace, A/C) control boards are typically a 820R-1k 3W resistor load. So 24-30mA AC typ. which is what I expect.
Like to "O" Heat/Cool, and "Y" Compressor (after loss of charge/pressure switch).

The control board already has 3-4 relays to deal with the higher power stuff. One large one for the outdoor fan, smaller ones for compressor contactor CC, reversing valve RV and what they call Defrost Heater W. What's funny is the control board relays are the same cube size as OP's: Goodsky RWH-SS-124DMF-U rated 15A.

There can be another (indoor) fan motor contactor we don't know about, and a timer board for the electric heater option as well. I suspect there's extra loads like these lurking somewhere that are responsible for the relay wear.

wonder what those relays cost and if i can source them...
as far as i am aware the only fans are in the outdoor unit
the defrost cycle is on a timer cause someone wanted to not pay extra

[sam_sam_sam]

Re: Mechanical Relay Quality

One thing that I always check on these boards are for bad soldering joints I have seen quite a few them with issues at terminals joints and at the relays joints as well and you are better off if the soldering joints looks questionable remove the solder and redo it you are better off in the long run

I have fixed a few them before when they either do not go into defrost or do not want to come out of defrost

Does this unit have a time delay for the fan to go off when the temperature hits the set point if does they quite often fail open which means they do not turn on the fan or the fan never turn off in auto fan control mode

[redwire]

Re: Mechanical Relay Quality

Digital inputs to HVAC (furnace, A/C) control boards are typically a 820R-1k 3W resistor load. So 24-30mA AC typ. which is what I expect.
Like to "O" Heat/Cool, and "Y" Compressor (after loss of charge/pressure switch).

The control board already has 3-4 relays to deal with the higher power stuff. One large one for the outdoor fan, smaller ones for compressor contactor CC, reversing valve RV and what they call Defrost Heater W. What's funny is the control board relays are the same cube size as OP's: Goodsky RWH-SS-124DMF-U rated 15A.

There can be another (indoor) fan motor contactor we don't know about, and a timer board for the electric heater option as well. I suspect there's extra loads like these lurking somewhere that are responsible for the relay wear.

[stj]

Re: Mechanical Relay Quality

32mA hold, but what was the inrush?

[redwire]

Re: Mechanical Relay Quality

Post #6 says you measured "0.67A up to 1A then back down" and now you're saying 32mA ???

I looked at Heil ICP Tempstar PA5536AKA4/PYPA36GA4 heat pump, from your picture. It looks just like an air conditioner but has a reversing valve to pump heat into the home and there's some optional electric heater package.
Power transformer is 24VAC 40VA. Based on pictures, you can figure out the schematic of the Heil control board 1087562/Honeywell 1084-83-100A, if I'm right about the one in your outdoor unit.
The thermostat inputs are low current going to a PIC MCU. There is no usual 24VAC inductive loads the thermostat relays would be seeing, like contactors etc.
So either your wiring is wrong and you are crowbarring something or this is a massive goosechase due to a cheap crappy Songle relay.

[evilkitty]

Re: Mechanical Relay Quality

Using my meter it showed ~32ma at ~27v AC

if i were to use 3 SSRs i would have to redo the pcb layout, but if i can sick with 2 relays it i can just swap them out and garage some wires at the relay for a new pin out/location
maybe i could use this relay: https://www.digikey.com/en/products/...1Z-4-5V/648227

[eccerr0r]

Re: Mechanical Relay Quality

Well, it seems a full amp can be passed through the circuit, so a 1A relay is pushing it.

Hmm... have to see what my thermostat is using now... I'm surprised it's not using a SSR, it too uses 3V logic (uses two AA batteries and probably residual power from the 24V control line)...

[sam_sam_sam]

Re: Mechanical Relay Quality

https://www.mouser.com/ProductDetail/817-SY-4.5-K

You can buy 3.3 volt solid state relays that run at this low of voltage you just have to search for them and if I was doing this I would highly recommend going this route

[evilkitty]

Re: Mechanical Relay Quality

https://www.mouser.com/ProductDetail/817-SY-4.5-K

[sam_sam_sam]

Re: Mechanical Relay Quality

Those relays ( if they are 24 ac ones ) are cheaply made in the first place and if your thermostat cycle to many times will wear them out in 3 to 5 years of use any way unless you get the heavy duty ones ( cost a lot more money ) which are hard to find only some Air Conditioning Supply House carry them and most of them require a journeymen license to buy from in the first place

These relays are mostly used to control fan speed between heating and cooling and sometimes used for heating element relays that are made for switching the heating element on and off if there is more than one heating element bank

[eccerr0r]

Re: Mechanical Relay Quality

404

[evilkitty]

Re: Mechanical Relay Quality

What about using this relay, it calls for 4.5v and says it will work as low as 3.2v
https://www.mouser.com/ProductDetail/817-SY-4.5-K

If this issue is the TIP120 would you expect both sides to wear like this? the NC (coil on state) wouldn't that one not look like this assuming the spring was not worn out, this contact does not look good, but it was not dead

i do not know for sure how much voltage the contacts are dealing with, i just know it is low amps based on wire gauge

[eccerr0r]

Re: Mechanical Relay Quality

The NO contacts get a weak make but the break works fine due to the spring.
The NC contacts get a weak break but the make works fine due to the spring.

Well it's something to consider in any case. You could use 2/6 of a 74HCT04 to make a buffer so the RPi output isn't as loaded to drive something you can use as a saturated switch. Or even drive a logic level MOSFET,... Would be nice to direct drive a MOSFET but a 3.3V signal limits the number of MOSFETs available without some sort of buffer.

I really think that TIP120 is a bad idea for this situation, if you were using a 12V relay and supply then the TIP120 may do much better.

[evilkitty]

Re: Mechanical Relay Quality

Actually using a TIP120?! This might explain the failure.

How much drive current can a rpi source/sink? If it can drive more, you're better off not using a Darlington there, at least for 5V. Maybe a 2N4401 would be better.

The old relay contacts are not pitted from arcing, but the plating has vanished and gone somewhere. There is no black soot so I'm puzzled what is going on. It might be chinesium plating.
Songle SRD-05VDC-SL-C coil is 70R or 71mA and they offer three different contact platings and current ratings 7,10,15A 250VAC as well as basic 10,000 cycle lifetime into resistive loads.
UL/CSA rate them only 3A 125VAC inductive loads, and there is a secret long life 100,000 cycle model. Thne specs are a bit deceptive and I've seen plenty of Songle knockoffs too.

Driving the relay with a TIP120, the base resistor is large 6k8 so the TIP120 sees about 0.2mA drive with hFE 500 so it is on a bit weak.
Changing to 2k gives 1mA drive from the RPi. The TIP120 loses at least a volt so the relay at best will see 4V.
If you drive the relay "weak" it pulls in slow and wimpy which would wear the N.O. contact only. The N.C. relies on the spring for force.

This is why I think the software might extra pulse the relay, or the snubber is simply too small for whatever the load is, or the relay quality is poor.

i got 10 of these relays in 2015 for $3.92 on ebay, so about 0.40 each, not sure if that is a realistic price for them

I have some 2N2222A NPN and 2N3906 PNP transistors on hand and a wide assortment of 1% 0.25W metal film resistors

rpi gpio is specked at 16ma max, however there is also a shared total max as well, i think that is 50ma, not sure if sinking and outputting both count towards this total
my LCD panel uses alot of pins, but the total ma should be silly low as i was trying to make the led a bit dim
front panel:

edit: i checked the voltage across the coil and got 4.14v on the bottom relay and 4.13 on the top relay
EDIT: took some pictures of the labels on the outdoor unit: https://imgur.com/a/809clTp they are not in great shape, but here they are

[evilkitty]

Re: Mechanical Relay Quality

you dont need a transistor for an ssr, they use an optoisolator and take under 5mA usually.

if it uses a 5v control i do need a transistor, my GPIO pins run at 3.3v

[stj]

Re: Mechanical Relay Quality

you dont need a transistor for an ssr, they use an optoisolator and take under 5mA usually.

[redwire]

Re: Mechanical Relay Quality

The old relay contacts are not pitted from arcing, but the plating has vanished and gone somewhere. There is no black soot so I'm puzzled what is going on. It might be chinesium plating.
Songle SRD-05VDC-SL-C coil is 70R or 71mA and they offer three different contact platings and current ratings 7,10,15A 250VAC as well as basic 10,000 cycle lifetime into resistive loads.
UL/CSA rate them only 3A 125VAC inductive loads, and there is a secret long life 100,000 cycle model. Thne specs are a bit deceptive and I've seen plenty of Songle knockoffs too.

Driving the relay with a TIP120, the base resistor is large 6k8 so the TIP120 sees about 0.2mA drive with hFE 500 so it is on a bit weak.
Changing to 2k gives 1mA drive from the RPi. The TIP120 loses at least a volt so the relay at best will see 4V.
If you drive the relay "weak" it pulls in slow and wimpy which would wear the N.O. contact only. The N.C. relies on the spring for force.

This is why I think the software might extra pulse the relay, or the snubber is simply too small for whatever the load is, or the relay quality is poor.

[eccerr0r]

Re: Mechanical Relay Quality

Actually using a TIP120?! This might explain the failure.

How much drive current can a rpi source/sink? If it can drive more, you're better off not using a Darlington there, at least for 5V. Maybe a 2N4401 would be better.

[evilkitty]

Re: Mechanical Relay Quality

i guess i could use a NPN and a PNP transistor and control them both with the same gpio pin each getting there own resistor, guess i should make use new pcb for this design, id need to take some parts off the old pcb, but they are easy ones to remove

[stj]

Re: Mechanical Relay Quality

no - atleast i dont think so.
using 2 and inverting the control signal on the second will work though.