Failure of DC to DC converter

[Doug Wolfe]

All,

Not related to my SBMS0 build, but a lesson learned and a question:

Learned a valuable lesson when doing some testing in full sun, pushed over 30V to my 24V to 12V converter and experienced a failure of the converter.  The failure unfortunately pushed full panel voltage straight through and blew the input cap in my inverter.  Has anyone experiences a similar failure of one of these units?

https://www.amazon.com/gp/product/B01LY8D7U0/ref=ppx_yo_dt_b_search_asin_image?ie=UTF8&psc=1

CAP replacement was luckily an easy 15 minute repair.  The pass through failure however concerns me...on some of my other rigs, I'm running several 12V electronic items directly from the 13.8V of the 24V to 12V converter.  What's the best protection for this?  Victron Battery Protect?

Doug

[Dacian Todea]

Doug,

Something must have been installed incorrectly as inverter is always connected to battery so inverter input voltage can not be higher than battery voltage.

Not sure where you are using that DC-DC converter as is sure not designed to have solar panels as input.  Also even if that failed I do not see how it will affect the inverter with has separate path connected to battery.

[Doug Wolfe]

Dacian,

This was bad on my part, I had no battery hooked at the time, was panel straight to the DC-DC converter, I knew better.  Also, my normal 24V inverters were in use, so I was using a small 300W 12V inverter behind the DC-DC, so that's how the 30V got pushed to it.  Several bad decisions there.

My concern now is that I didn't realize those converters would fail in a manner to pass the higher voltage straight through.  Trying to determine the best safety mechanism to put between DC-DC converter and the 12V distribution blocks to protect 12V DC electronics.

Attached pic is example of ONE of my off grid systems.  This one runs a router and mifi to provide internet for blink cameras at an off-grid location.

My SBMS system is still running in test mode on another system, but will also have a DC-DC converter with the same type of router and other 12V.

[Greg Kowieski]

Wait, what!  I'm actually installing that same converter this weekend.  Are you saying that the converter passes more than 12 volts on the output of the converter?  I mean, that defeats the purpose of the converter!  Ima use it for a paper weight if that's the case.

I'm going to hook my input to the pos and neg bus bars off the battery.  That way I have maintained DC flow to the 24->12 vdc controller.  Also, I noticed on your rig, you have a pre-charge setup.  I'm using the SBMS0 to turn on/off my inverter and have always wondered if I should use a pre-charge resister between the inverter and the battery.  And for that matter, do we really need anything between the panel->DSSR20->battery?

[Dacian Todea]

Greg,

The DC-DC converter will not output more than 12V if used normally and not abused. What happened to Doug is that he basically connected the DC-DC converter to PV panels open circuit voltage way higher than spec 24V and so the converter was damaged and thus it outputs the same voltage as input because of the damage.

He has a switch between the battery and inverter so in that case he will need a precharge circuit before switching that switch ON. If you have the inverter directly connected to battery you only precharge the inverter once when you did the connection.

You will need a circuit breaker or fuse between DSSR20 and battery to protect the cable connecting battery to DSSR20 in case you ever short that wire to GND (battery negative). The fuse or breaker will be close to the battery as that si the source of unlimited current and you need to protect the wire.

[Greg Kowieski]

Thank you.  I just have one question.  Do you ever sleep!   

[Dacian Todea]

Hi Greg,

Apparently I do :) else I will not be alive. My sleep schedule may be offset but I do sleep more in the morning so is all good :)