I am troubleshooting why our Victron Buck-Boost DC-DC converter is not charging our LiFePO4 house batteries in our camper van. We recently went on a trip from NY to Vermont. Since it was cloudy the solar panels did not keep up with our demand, so our house bank got down to about 70% state of charge. In the past, the buck-boost would kick in while we were driving and top up the house bank. However, not so on this trip.
Configuration: The buck-boost input (IN) terminal is wired to the van starter battery terminal. The output (OUT) and ground (GND) terminals are wired to the house battery bank positive and negative bus bars, respectively. I’ve checked out all the connections and they are good.
I’ve tested the connections with a multitool, and here are some results:
Buck-boost output terminal to batteries: 13.7 V. This voltage is the same as at the house battery terminals. The batteries are charged to ~100%. The output light is blinking green, which according to the instructions “Green: converter off, battery voltage normal.” This all looks good to me.
Buck-boost Input terminal to van starter battery, with van running: ~1V. The van ran for 20 minutes or so and this did not change. I don’t know if this is a normal voltage at this terminal when the house batteries don’t need a charge. The blue light at this terminal is flashing, about once a second. The instructions read “Blue, quick flash: engine running, converter will start after preset delay. Blue, slow flash: the converter is OFF and activation is blocked due to low input voltage.” Does anyone know what a quick vs. slow flash is? And what is the low input voltage?
Cable from van starter battery to buck boost terminal: I disconnected the cable from the buck boost and tested it. 12.9 - 13.0 V (with van running). This suggests to me I’m getting good power from the van starter battery to the buck-boost.
The above conclusion is wrong.
When you disconnect the cable there is no load on it so even with a very poor connection you read the battery voltage because a multimeter takes little current. Once you have the device connected to the buck boost there is a load the voltage collapses.
You most likely have a loose terminal, partially blown fuse or isolation switch that is making poor contact. This could also be on the negative cable but more likely the positive. When the buck boost is connected use your multimeter on each connection, fuse or switch to find where 12V turns to 1V.
I have retested the connection from the starter battery to the buck-boost by connecting a test lead extension to the starter battery negative and then testing at the positive input terminal on the buck boost. With the van off I’m getting 12.5V and with it running 14.7V. I also looked at the terminal connections and wires on both ends and they look OK.
The TSConfig software that is connected to the buck boost is showing 1.1V input voltage and is showing a yellow status. (Setting 1 on the software). The software’s instructions say: “Converter input voltage.To convert, the input voltage must be higher than the undervoltage threshold (setting 24). When the input voltage drops below the undervoltage threshold, the LED (at the input) is yellow to indicate that converting is blocked.” The undervoltage threshold (setting 24) is at 11.9V.
I suspect there is a problem with the unit itself, but appreciate any additional input you may have.
I replaced the buck-boost and still getting <1 volt reading on the TSConfig software and no charging of the house bank. I have checked all the connections again from the starter battery to the buck boost and to the house bank (note, I’ve pulled apart my camper van to do this!). They all look fine. I can’t find any chafing or cuts in the wire, but part of it runs through a tube under the van so I can’t see it.
My multi-tool testiing shows no voltage drop from the starter battery to the end of the wire connecting to the buck boost input. The wire is 8 Gauge Powerflex Pure Copper Ultra Flexible Welding & Battery Cable from WindyNation. It’s rated to 55 amps. The buck boost is the 50 amp version.
I’m now a bit frustrated and looking for some suggestions!
All I can suggest is disconnect the wires from buck-boost and connect them to a 12V load and then check the voltage again under load to see if there is voltage drop or not. The larger the load, the better the test, but something like a headlight bulb at 60W would pull 5A and give you some indication as that should show negligible voltage drop. The other thing I have done in the past is get a long length of wire with crocodile clips / banana plugs on to check resistance along a cable section using your multimeter so you can connect to a long cable in different parts of a vehicle / boat.
Do you have any resettable breakers in the circuit of the type shown below. These have a bad reputation as there are lots of cheap ones available that often have poor switch contact and high resistance. Use reputable ones such as Blue Sea, but again make sure they are actual Blue Sea and not fakes.
Mystery solved. The buck boost ground wire is connected to the house system negative bus bar, and it turns out that is not grounded to the chassis, so the loop from the starter battery to the buck boost is incomplete. Using a long test lead I connected the buck boost ground terminal to the starter battery negative terminal and I get a good reading of 12.4V on the TSConfig software.
Now, I just have to figure out how to ground the negative bus bar to the chassis…
Glad you found it, it had all the symptoms of a lack of continuity but I could not have diagnosed the house batteries were not connected to chassis ground from the voltages. I will remember that for the future. Thank you for confirming.
