I’ve read some concerning posts here about the relay outputs on Cerbos getting welded or otherwise ruined by trying to use them to drive relay coils without adequate flyback protection. In my case, I’m trying to control about 10A to 15A of heat tape load (battery heaters) @ 12VDC. I’m an experienced EE, but I generally work with digital and low-power analog.
While I can certainly use relays with internal diodes, my tolerance for a blown Cerbo is less than zero.
Other options:
Drive the LED side of an opto isolator with the Cerbo relay, then use the opto output to drive the relay coil. If a Cerbo relay can be blown by 3 to 5V and a few mA of current, that would be amazingly bad.
Drive a FET with the relay output (power connected to FET gate through relay, pulldown/up to hold FET off when not energized). Load through FET source/drain. Very simple and reliable, or should be. But the Cerbo manual only talks about relays and optocouplers.
Replace the relay in the #1 with a FET.
Use the Victron S104. Expensive, still needs another relay to carry the load.
Relays are nice and cheap and require nothing more than wires to quick connects, so that’s very attractive. But a blown Cerbo is not worth it.
Anyone with experience in the specific case of driving moderate (>10A, <100A) DC loads from the Cerbo relays?
I have indeed read that people had defective Cerbo Gx relays due to certain (over)loading. Most likely, the Cerbo GX relays are somewhat more fragile than the specified specifications say, or they cannot withstand current peaks that well.
In my case, I switch a second relay with the Cerbo relay, because of the high load.
It’s a Bosch 12V/10A automotive relay, with suppressor diode, and that works ok for about a year now.
The amp rating for the Cerbo GX relays were below what I needed so I implemented an external relay that could handle the load. I needed a relay that worked with a 48 volt system that I could put in my breaker box on DIN rail.
The Cerbo relays are only rated to a maximum of 6A at up to 30vDC, and 1A above that, so you’d need an external relay in any case for your stated load.
Thanks, yeah, I understand that. I was asking about what the relays in the Cerbo can tolerate since apparently they are welding with moderate loads that are within the rated limits.
They usually fail because people do not understand start up loads or shut down voltage spikes, they connect a power supply rated at 4A but do not understand the input capacitors will take many times that on start up, or a motor or relay. I expect you have seen the FAQ