Frame grounding - best contact?

[dbsoundman]

I ran a 2/0 DC ground cable from my interior house system to the frame of the bus so I can utilize the bus body as a ground for lighter duty items among other reasons. I’m beginning to wonder if I’m still having some issues with bad contact on the frame as I’m having some intermittent issues losing all DC power in the house system (even the BMS goes dark). I crimped a proper lug on my cable and used a stainless bolt, lock nut, and star washer through an existing hole to connect to the frame. I also used a grinder to try to clean up the frame to bare metal before tightening everything down. Finally, I put a light coat of black spray paint on everything to inhibit rust.

Is there anything else I can do to ensure better ground contact? I know the starter batteries have a welded stud that connects to the frame but that stud is not long enough to accommodate the house battery lug nor is the house battery cable long enough to reach that location. I haven’t had a chance to really troubleshoot my issue physically yet but bad grounding is always the first suspect.

[Rucker]

Ideally the resistance through a chassis as measured by ohms would be near zero however I'm told you can't really use an ohm meter to check your chassis' resistance.

If you're curious, I think you can get an idea of the resistance by subtracting the voltage on the negative side of the device from the voltage on the positive side of the device when it's under load. The difference is voltage drop, which can be equated with resistance on the return path.

Not sure if anyone else has some practical experience in checking chassis resistance.

[Rwnielsen]

You my have to bond your frame to the body. There may be isolation mounts or something causing an intermittent issue. Similar to how cars have a bonding wire from the motor to the frame. Pick up or make a short cable and bolt it to a solid point on the body and the frame, just like you did with the house ground.

[Booyah45828]

The cable you made might be fine, the buses cable from the batteries to the frame might be bad, or it might not be large enough. Often times on commercial vehicles they'll ground the batteries to the starter/engine itself and then jump from that to the frame, as the body/frame uses very little power compared to the engine/starting system.

Use a multimeter and see what the voltage at the device is. If no volts are present, use long leads back to the battery and check each run individually. Resistance with an ohm meter can be used, but sometimes it will only tell you so much. Rucker has the right idea with voltage drop, as once your dealing with large amounts of amps, voltage drop is the way to check for resistance on those large gauge circuits. Youtube it if you want to learn more about voltage drop and how to measure it.

FWIW measuring voltage at the device and subtracting it from the voltage at the battery would give you the voltage drop of both sides of the circuit. To measure only the return, you'd measure volts from neg at battery to neg at device. Same with the supply, you'd measure pos at battery to pos at device.

I'm not sure how your system is designed, but IMO the run between the battery bank and the house system should be as short as possible and ran with direct wires of appropriate size. For instance, I wouldn't have my battery bank in the rear of the bus with the inverter/charger and bms located at the front. Have the bank and system located next to one another, at most separated by a firewall or cabinet.

[ewo1]

Originally Posted by Rwnielsen

You my have to bond your frame to the body. There may be isolation mounts or something causing an intermittent issue. Similar to how cars have a bonding wire from the motor to the frame. Pick up or make a short cable and bolt it to a solid point on the body and the frame, just like you did with the house ground.

This is sound advice.
You could potentially have two ground reference points which might confuse your BMS.
Bus bodies are clamped down to the frame but age, and wear and tear by the constant vibrations between the body and frame could possibly loosen up those clamps and create poor grounding/continuity.

I would but a ground strap from frame to body just to ensure it is done and Eliminated.

[dbsoundman]

Thanks all. The house batteries and BMS are all together in the front of the bus behind the driver's seat, and so the frame ground for the house batteries is actually not far from the starter battery ground - just a couple feet away.

My higher current appliances (diesel heater, vent fan, and I think even my USB charging locations) all have ground wires going right back to the electrical box behind the driver's seat where I do all the distribution. The only body grounded items are interior lights (because I reused the original lighting) and maybe a couple other small things. The other day when I saw there was no power, there was no power ANYWHERE, no matter where it was grounded. Even the BMS was dark. I will definitely work on putting in my own body to frame grounding strap (any recommendations on what to make it out of - battery cable or something else?).

Some more clues I forgot to write down last night: at one point for a couple months I had issues where the system components would work fine at night when we went to bed, then usually right after we got up in the morning, the power would go out (except for the BMS). It took me an embarrassing amount of time to realize that one of the negative post bolts for my house batteries was not actually tightened down. Then, this winter it got super crazy cold outside, like -10 F, and we were trying to keep the interior of the bus warm. For whatever reason our shore power charger wouldn't turn on (or maybe the BMS went dead? I can't remember), so I ended up doing something really weird: I got the trickle charger for the starter batteries to work, and then basically connected the starter batteries to the house batteries through the normal DC-DC charger I use when the bus is running. Basically, I was trying to use the trickle charger THROUGH the starter batteries to charge the house batteries. I was desperate.

All of this is to say I'm wondering if maybe I did some damage to my AGM batteries as well. I can't find a definitive way to test them automatically but I'm wondering if maybe I need to test each battery individually or float charge them or something.

(Side note: kids, don't cheap out on these things. If I could go back in time I would have just bought all Victron stuff like everyone else instead of getting this Bogart BMS and AGM batteries. The Bogart wifi adapter stinks and while the system is simple and fairly intuitive it just doesn't offer that much insight into the system health. And AGM batteries clearly don't offer any reliability benefit over lithium like I had thought.)

[rossvtaylor]

Since this is how the electrical wizards at Epic Skoolies attached the main house bank ground in a (very expensive) bus build, it must be the right way to do it.



Okay, back to the serious discussion and real advice...

[dbsoundman]

Originally Posted by rossvtaylor

Since this is how the electrical wizards at Epic Skoolies attached the main house bank ground in a (very expensive) bus build, it must be the right way to do it.

Attachment 71101

Okay, back to the serious discussion and real advice...

That sure is epic...epic-ally bad!

[Rucker]

Originally Posted by dbsoundman

<snip>

(Side note: kids, don't cheap out on these things. If I could go back in time I would have just bought all Victron stuff like everyone else instead of getting this Bogart BMS and AGM batteries. The Bogart wifi adapter stinks and while the system is simple and fairly intuitive it just doesn't offer that much insight into the system health. And AGM batteries clearly don't offer any reliability benefit over lithium like I had thought.)

I've written a few rants about battery management systems already elsewhere in this forum.

I have a Daly BMS so by necessity I've become semi-expert in troubleshooting. Are you able to check continuity between the shunt and the frame? Can you tell whether the BMS is cutting power but not telling you it's doing that? Can you measure voltage at the battery, and check it under load?

[Rwnielsen]

Originally Posted by rossvtaylor

Since this is how the electrical wizards at Epic Skoolies attached the main house bank ground in a (very expensive) bus build, it must be the right way to do it.

Attachment 71101

Okay, back to the serious discussion and real advice...

I don't know how you do it Ross, I'd be tearing my hair out.
Ground screws can't be self tapping and should be green

[Booyah45828]

I see 3 bolts/nuts in the picture that would have been better off utilized as a ground then the cheap self tapping screw that was.......

I'm not sure if that's incompetence or laziness or both, but it's definitely something.

[Tejon7]

Why would the clever folks at Epic spend the extra time to properly attach that lug to the frame when lug and cable are barely holding together? Looks like they crimped that with a pair of channel locks and a healthy dollop of harbor freight electrical tape to hide the evidence.

[mmoore6856]

when dealing with suspected ground issues make a 30 foot jumper wire . hook it directly to the negative post . hook it to your test meter ,turn on your 12 volt appliances then with you meter on dc volts follow every ground connection from the frame to the negative side of every appliance. when you get upstream of a bad connection your voltage will go up on your meter

[Rucker]

Originally Posted by mmoore6856

when dealing with suspected ground issues make a 30 foot jumper wire . hook it directly to the negative post . hook it to your test meter ,turn on your 12 volt appliances then with you meter on dc volts follow every ground connection from the frame to the negative side of every appliance. when you get upstream of a bad connection your voltage will go up on your meter

This is exactly the practical advice needed for our OP. DB, I know I asked a bunch of questions earlier-hoping not to bombard you but I'm still curious about your setup and what kind of troubleshooting you are able to do.

[mmoore6856]

sometimes you got to make your own test tools. i worked on a old mack that had tail/brake issues that the company mech could not figure out. he was grounding his test lite on the frame by the tail lites. i grabbed my 30 foot jumper and went to the battery and found it worked. ended up it was 3 ground issues tail lite to box,box to frame and frame to starter (neg on mount bolt) always remember it must make a complete circle on dc voltage. i also used it on the hot side to see if it was a supply issue. over the last 40 years i have used it many times and loaned it out [and lost a few] but it is a sure way to eliminate the connection laden ground systems.

[dbsoundman]

Originally Posted by Rucker

This is exactly the practical advice needed for our OP. DB, I know I asked a bunch of questions earlier-hoping not to bombard you but I'm still curious about your setup and what kind of troubleshooting you are able to do.

I am definitely experienced with electronics but a full scale DC power system has been more problematic than I expected. I'm used to working with data to troubleshoot issues and find trends and until today I didn't have that data so I was a little lost here.

Today, I went out to the bus, and found that the system had lost power and came back on its own, as it's been doing lately. I knew this because the inverter was off, and usually I leave it on. I turned the inverter back on, and paid close attention to the current/voltage readings I get to my custom Home Assistant dashboard. As of about an hour ago, I saw the inverter current increase, indicating the inverter switched up because the refrigerator kicked on. Typically when this happens the voltage goes down by maybe 0.3 volts; this time, the voltage went down from 12.7 to 11.8, then I haven't gotten a new reading since then. This tells me that I either have a weak ground connection somewhere, or that I might have an inverter issue. DATA, FINALLY!

I have a Xantrex Freedom X 3000w inverter, FWIW.

[Rucker]

Those induction motors need a lot to get going (inrush), and you probably know.

I have heard that damaged batteries may look like they charge, and even hold a charge, but as soon as they are put under load their voltage can sag very quickly. I test my system with a heavy duty electric drill that draws about 20 amps at max power. With a DC amp clamp I'm able to do some load testing. Might be worth considering, especially if you think the batteries are potentially damaged.

edit: or if you are playing around with BMS settings.

[dbsoundman]

I still need to 100% verify my frame grounding, but at this point the problem seems to be the batteries. I unplugged the fridge yesterday and left the inverter on with no load and one of the interior lights on (LED so very low current), by about 9am this morning the system was dead and I saw a very similar ~1V drop in battery voltage right before it went offline. I think it's safe to close out this thread and move on to my next one...