DCDC low voltage issue

Adrob

New Member
Hi Everyone,
I'm new to the forum and have my first question... I bought a T6 camper about a month ago. It's come with a few teething problems, one of which was the split charge system being a VSR... So after reading through the forum I've swapped it (and the dead leisure battery) for a victron 12:12 30.... All seems great until the charger goes into Bulk mode.

When it's in bulk mode I'm seeing voltages as low as 6v (engine side, with engine running), which clearly triggers the low voltage lockout but also switches the unit off. This makes the sargent unit start beeping and means the leisure battery isn't charging.

Any ideas of what I need to do next? Anyone seen this before? Is it volt drop over the cable?

Any help is appreciated. Thanks Al
 
Where and how are you measuring that input voltage ?
It does sound like a poor connection to the point where that voltage is being measured - can you trace it back through the wiring ?
Some photos might help.

Pete
 
Post some pics.

I'm assuming cables are too thin.?

Poor connection.?

Bad ground.?

All of the above will cause, volt drop.
 
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This is my 12.12.30.

30A DC-DC with the 12v IGN H terminal connected so it switches ON when engine running. (well BCM Engine RUN signal)

Full rate 30A charge... No volt drop on. Starter side or Leisure side.

Lithium profile into a Poweroad 100A LB.

20210811_183736.jpg20210811_183724.jpgScreenshot_20210812-062353_Poweroad.jpgScreenshot_20210812-062705.jpg
 
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It gets HOT when running at full rate !!!! (All lithium battery s will pull 100% from the charger till battery full)
 
Ok, thanks will get some photos today..

I've measured from two points:

1) a dodgy Amazon 12v circuit breaker (measured input as 14v output was fluctuating when I move it slightly) - new one arrives today..

2) so directly connected charger to battery (held it on) and the victron app showed the input voltage droping when it tries to bulk charge.

The dcdc is located in the back of the van (where the old VSR was) next to the leisure battery..

Would fitting the dcdc nearer the engine battery be better?
 
The dcdc is located in the back of the van (where the old VSR was) next to the leisure battery..

Would fitting the dcdc nearer the engine battery be better?
It still sounds like a poor connection somewhere, but larger cables will improve the volts drop over a long length.
So if you move the dc-dc closer to the source you will improve the volts drop and perhaps beef up the cable going from the new location to the rear.
 
Ok, so an update. I've rewired the dcdc with bigger cables (what a nightmare feeding that through the van was!).

Sad bit, I still have the issue much less but it's still occuring.

Video of what I see in the app is here

Any advice appreciate thanks

16296458988612124811829778315550.jpg

16296459398231312324308462129323.jpg
 
The output and ground cable look way to small to handle 30A.


How long is each of those cables?

Use a jump lead as a new temporary ground.

And retest.

And replace the output cable for same thickness as input.

Post a pic of the LB connection, and the ground connection.
 
Thanks Dell, I bought those off Amazon claiming they were for 30a and when they arrived was surprised.

I've got some of bigger cable prep'd will try that later.

Ta
 
Hi, Tried the bigger cables still dropping out. I use the rear door latch as an earth and I'm wondering if that made it slightly better... Is there a particularly good earth point in the right rear corner? Might try that next.
 
This still sounds like a volt drop issue and you mention that the DCDC is in the rear corner of the van.

For a 12 volt system a cable run carrying 30 amps would need to be:
For 1 metre length:
For 1% loss 10 sqmm
For 5% loss 4 sq mm

For 6 metres:
For 1% loss 70 sq mm. (Clearly massive and fairly impractical, but it demonstrates the issue.)
For 5% loss
16 sq mm.

This shows the massive effect of problems caused by cable length and i am fairly sure this is your issue.

incidentally what have you set your engine shutdown parameters at?
C1514F79-4DAA-43A0-A768-FFFAB703AEAD.png
 
Ah not sure I could stomach swapping the cables again but at least I could join them together and pull them through but there's not much space in there.

In terms of engine off detection, I've turned the original battery cable into an ignition feed and wired in as per Dell's advice (h terminal from memory) - it's just out of shot from the image I used some left over cable to test it out....
Works perfectly, no longer worried it's stayed on after engine stopped, though it was pretty good.
 
So, the saga continues. After rewiring everything, hooking up a new earth to the underside of the vehicle I'm still getting the issue.

Suppose the only option now is to test the victron connected next to the engine battery (must remove all possibility of volt drop engine side but I get that it reduces my LB charge efficiency).

I guess my questions are:

Anyone see a problem mounting the dcdc in the engine bay?
And before I do this is there any chance the victron unit is faulty?

Thanks for the help!
 
Measure the actual voltage drop, i.e. measure voltage at the start and end of the cable run whilst charging in bulk mode to see if you have a problem. If voltage drop is the issue, shifting the victron may not help - will just switch the issue from input to output…
 
the DC-DC is supposed to go closer to the LB.

its not waterproof . . . and the heatsink can get very hot . . so ifd be cautious about fitting in engine bay.

im still sure volt drop is the issues over the link cables.

try running a temp FAT heavy duty cable outside the van to the battery fuse.

NOTE: most people fit the unit MID WAY ie under the drivers seat.

can you use a set of jump leads as a temp test? - just for the starter POS link?
 
for a 5m cable run, drawing 30A @ 12v nominal, we are looking at a 10m2 cable (for under 5% volt drop)

what size cables are you using? - what printed on the side of the cable? - got a pic?

1630232995638.png








+++
 
for a 5m cable run, drawing 30A @ 12v nominal, we are looking at a 10m2 cable (for under 5% volt drop)

what size cables are you using? - what printed on the side of the cable? - got a pic?

View attachment 128635








+++

That’s a two way run, i.e. 10m. Should be less than that assuming chassis ground is decent. Ground could be an issue though, like everything else, it needs measuring.
 
this cable looks good.

10m2 - (70A) £3.50 pm



1630233174300.png



though i would prob go for 16m2


1630233238240.png




or even 25m2 . . .


1630233267722.png
 
So, the saga continues. After rewiring everything, hooking up a new earth to the underside of the vehicle I'm still getting the issue.

Suppose the only option now is to test the victron connected next to the engine battery (must remove all possibility of volt drop engine side but I get that it reduces my LB charge efficiency).

I guess my questions are:

Anyone see a problem mounting the dcdc in the engine bay?
And before I do this is there any chance the victron unit is faulty?

Thanks for the help!
post some new pics of the cables,

connections on dc-dc,

connection to ground,

connection to starter battery,

connection to LB,


what size cable are you using for each bit of the run.

also that ebay trip switch in engine bay is not advised ( they get very hot and add a large resistance to cable) - try swapping out for a MIDI fuse & holder. (thr proper marine grade ones are ok, just not the ebay cloans)

.
 
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