On Tuesday, October 20, 2020 at 1:26:30 AM UTC-5, wrote:
On Sunday, October 18, 2020 at 9:50:21 PM UTC-4, dtga... wrote:
I have a Harbor Freight Cen-Tech Battery charger SKU 60653. I was attempting to charge my riding mower battery when it fried. I inspected the insides and found that the thermal fuse was melted and a relay had burned out.

I replaced the relay with the same Songle Relay SRU-06VDC-SL-C type. The thermal fuse was different. I used a 50A Auto Automatic Reset Stud Type Circuit Breaker for the thermal fuse.

When I plugged it in and attached it to my mower battery it lite up and seemed to be in a cycle of charging. I had it set to 2 amps. I assumed by the noise it was making, buzzing followed by silence. Only thing was the analog meter wasn't moving, it was stuck at 100%. After a few cycles it popped and started smoking. The SRU-06VDC-SL-C relay went out in the same spot the original did. There is a metal leg? in between 2 others and this continues to blow out. I resoldered a 3rd one and it blew the same spot.

Can anyone suggest what I should be test/measuring and why the relay keeps going out? I'm not giving up on the charger just yet.

I didn't test any of the diodes. Not sure how yet.
Harbor Freight, like other companies that sell battery chargers don't release service data. You can only test the common failures like shorted diodes, or other components. Do you have a meter to read resistance? Diodes connect in one direction. If they show zero resistance in both directions, they are definately shorted. That relay is intended to protect the charger and battery from being connected backwards. These 'intelligent' chargers sense the polarity and a minimum voltage to stop you from using it on a six volt battery. Since the relay was damaged, I would look for a short on the area between it and the battery clips, first.
Diodes with zero, check. Look for short circuit, check. I replaced this with a Stanley Charger but I still want to try and salvage it and learn more. I'm pretty sure I blew this charger by overusing the 50a engine starter on my mower. I do have a multimeter. I bought a 10 pack of the relays on ebay for cheap so I have many left over. Thanks for the info you provided..