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RiversToTheSea
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Joined: June 22, 2022
Posts: 69
Location: PNW
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 Posted: Fri Jun 13, 2025 6:27 pm Post subject: Re: Two nights, three day trip: what worked, what didnt |
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Thanks, that's very helpful. I'm now a bit frustrated that the Victron manuals are online only and I didn't discover that one.
This weekend's plan is to open up the Winnebago interior to run wiring for a backup camera, so it will be a good time to run a heavier gauge wire for the DC charger (and maybe swap it out for the smaller 18A charger as someone else suggested). |
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RiversToTheSea
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Joined: June 22, 2022
Posts: 69
Location: PNW
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| Posted: Fri Jun 13, 2025 6:30 pm Post subject: Re: Two nights, three day trip: what worked, what didnt |
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| xEVC wrote: |
I think, with the DC DC charger in circuit, there's no need for the relay any longer, because it can sense the starter circuit voltage and stay OFF when the engine is not running. |
Yeah, I went back-and-forth on removing it, and opted to keep it in for the redundancy in case the Victron starter sense didn't work right for some reason. I also suspect its switch contacts may be very dirty after thirty years of service. I'll do a bit of testing but will probably remove it. |
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RiversToTheSea
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Joined: June 22, 2022
Posts: 69
Location: PNW
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| Posted: Fri Jun 13, 2025 6:35 pm Post subject: Re: Two nights, three day trip: what worked, what didn't |
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| Stripped66 wrote: |
Regarding the 9VDC measurement, there's some details not posted here, including the actual voltage and the duration only 9VDC was being detected. I'm inventing a scenario here, so feel free to challenge its plausibility: if the alternator's voltage regulator cut the voltage output (perhaps at high combined load during idle, or maybe the voltage regulator is going south) leaving the starter battery alone to supply this load, the resulting voltage drop at the starter battery, plus the voltage drop across 20' of wiring, could put the detected voltage at the charge controller below 10VDC.
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Yeah I should have added more details to my original post. What we observed was this: Victron app open, DC/DC charger screen up, the charger would report charging at 5A or so. Then after about fifteen seconds report off due to low battery voltage. Then about five seconds later would report charging again. Switching to the BVM screen would report substantially the same. DC/DC charger providing +5A at 13-ish volts, then would drop down to 9V and shut off, and after a few seconds would recover back to 13V and turn on again. |
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xEVC
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Joined: March 23, 2017
Posts: 130
Location: California
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| Posted: Fri Jun 13, 2025 7:04 pm Post subject: Re: Two nights, three day trip: what worked, what didn't |
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| RiversToTheSea wrote: |
... the charger would report charging at 5A or so. Then after about fifteen seconds report off due to low battery voltage. Then about five seconds later would report charging again. Switching to the BVM screen would report substantially the same. DC/DC charger providing +5A at 13-ish volts, then would drop down to 9V and shut off, and after a few seconds would recover back to 13V and turn on again. |
That's very interesting - First, the 5A value is what you thought it should be (due to your cooler).
But the on/off resetting is weird: if this were on my van (2000) I would suspect that the 40A auto-reset breakers were tripping then resetting (there are two in the house battery circuit). But your 1995 doesn't have these auto-reset breakers at all, right?
However, a high resistance relay might also behave this way: the DC DC charger starts charging, but as it ramps up the amperage, the high-resistance connection causes a larger and larger voltage drop; eventually it goes below the "low voltage cutoff" and resets.
Perhaps it tries again a few seconds later, only to repeat the pattern?
If you clean up the bad connection(s), I thihk you might be able to keep the current DC DC charger, as long as you turn down the charging voltage a bit. LFPs can happily take 14.4V or 14.6V bulk charging, but will gobble a ton of current.
I bet if you turn the charging voltage down quite a bit (14.0, maybe as low as 13.6) you would still get a solid LFP charge, but it won't be doing it at 30 to 40Amps.
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2000 Eurovan Camper (Winnebago)
Upgraded with 16" wheels |
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dsh1705 
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Joined: June 11, 2014
Posts: 130
Location: Seattle, WA
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| Posted: Fri Jun 13, 2025 7:12 pm Post subject: Re: Two nights, three day trip: what worked, what didn't |
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| 1995 doesn't have these auto-reset breakers at all |
The 95 has (2) 40 amp breakers in the line to the house battery (firewall and on the battery box).
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David
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95 EVC
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Stripped66
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Joined: May 31, 2005
Posts: 3508
Location: Charleston, SC
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| Posted: Fri Jun 13, 2025 8:34 pm Post subject: Re: Two nights, three day trip: what worked, what didnt |
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| RiversToTheSea wrote: |
| My wife was driving and I was adjusting the settings in the DC/DC charger to try to diagnose the problem. At idle and when cold I get 14A out of the alternator, and I had the Engine Start Sense feature turned on, with the lower limit at 13.2V or so. But after a couple of hours driving when the DC/DC charger was dropping out I set the starter sense voltage lower to see if that helped. I knew when I set it to 12V and the DC/DC charger was still dropping out something was amiss. I set it to 9V just to see how low the supply voltage was going, I didn't expect that this was normal at all. At that point I turned the DC/DC charger off. |
I missed this earlier.
"starter sense voltage"...do you mean the Shutdown Voltage? The Shutdown Voltage should be less than the Start Voltage, so I suspect this is what you mean by "lower limit". (but, you could also be referring to the Input Voltage Lockout)
Was your Shutdown Voltage initially set to 13.2V, and then you lowered it to 12V, and then you lowered it to 9V? This would explain most of the issues you've described...
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| 66brm wrote: |
| Bodacious wrote: |
| Why not just make a custom set of wires with a Y splice in them. Then you could just run one distributor. |
I don't think electrickery works that way |
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RiversToTheSea
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Joined: June 22, 2022
Posts: 69
Location: PNW
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| Posted: Sat Jun 14, 2025 12:20 pm Post subject: Re: Two nights, three day trip: what worked, what didn't |
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| dsh1705 wrote: |
| Quote: |
| 1995 doesn't have these auto-reset breakers at all |
The 95 has (2) 40 amp breakers in the line to the house battery (firewall and on the battery box). |
Mine has neither of these. The wiring is a bit non-standard. There's no DC + isolation post in the left rear compartment, no 40A breaker on the firewall next to the isolation relay, and no breaker in the rear compartment that I've found.
This weekend's project is running wiring for a backup camera, so I'll be taking most of the passenger-side panels off/out to run that. I'll investigate further. |
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RiversToTheSea
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Joined: June 22, 2022
Posts: 69
Location: PNW
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| Posted: Sat Jun 14, 2025 12:24 pm Post subject: Re: Two nights, three day trip: what worked, what didnt |
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| Stripped66 wrote: |
| RiversToTheSea wrote: |
| My wife was driving and I was adjusting the settings in the DC/DC charger to try to diagnose the problem. At idle and when cold I get 14A out of the alternator, and I had the Engine Start Sense feature turned on, with the lower limit at 13.2V or so. But after a couple of hours driving when the DC/DC charger was dropping out I set the starter sense voltage lower to see if that helped. I knew when I set it to 12V and the DC/DC charger was still dropping out something was amiss. I set it to 9V just to see how low the supply voltage was going, I didn't expect that this was normal at all. At that point I turned the DC/DC charger off. |
I missed this earlier.
"starter sense voltage"...do you mean the Shutdown Voltage? The Shutdown Voltage should be less than the Start Voltage, so I suspect this is what you mean by "lower limit". (but, you could also be referring to the Input Voltage Lockout)
Was your Shutdown Voltage initially set to 13.2V, and then you lowered it to 12V, and then you lowered it to 9V? This would explain most of the issues you've described... |
I'm probably misremembering it, and it's a little frustrating that the Victron app for the DC charger won't see it unless the DC charger is running. Anyway, to answer your question: Yes, the 'turn on' voltage is set higher than the 'turn off' voltage, and when I noticed that the voltage reading for the starter battery kept dropping below the 'turn off' voltage, I kept lowering the 'turn off' voltage. And of course once it got below 12V I knew something was wrong, it should not be that low when driving/alternator on. I kept lowering it to see how low it had to be just to get that data point, once I got to 9V I turned the DC charger off completely. |
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Stripped66
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Joined: May 31, 2005
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Location: Charleston, SC
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| Posted: Sat Jun 14, 2025 1:13 pm Post subject: Re: Two nights, three day trip: what worked, what didnt |
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| RiversToTheSea wrote: |
I'm probably misremembering it, and it's a little frustrating that the Victron app for the DC charger won't see it unless the DC charger is running. Anyway, to answer your question: Yes, the 'turn on' voltage is set higher than the 'turn off' voltage, and when I noticed that the voltage reading for the starter battery kept dropping below the 'turn off' voltage, I kept lowering the 'turn off' voltage. And of course once it got below 12V I knew something was wrong, it should not be that low when driving/alternator on. I kept lowering it to see how low it had to be just to get that data point, once I got to 9V I turned the DC charger off completely. |
You really need to review section 5 of the manual until you understand the charging behavior depicted in Figure 8.
Here's what's going on:
Any time the starter battery voltage is above the Shutdown Voltage, the charger is trying to charge the house battery at 30A.
Consider xEVC's estimate of voltage-drop along your undersized wiring from the starter battery to your charger...1.25V @ 40amps. This is reasonable, IMO. If your alternator is putting out 14v, and there is a 1.25V drop between the starter battery to your charger, your charger is seeing only 12.75V once it begins pulling 30-40A. Best case scenario.
When your Shutdown Voltage is set to 13.2V, the charger tries to pull 30-40 amps, voltage immediately dips below the Shutdown Voltage, and the charger begins to throttle back current. That's probably the 5A of charging current you've seen. But, because the charger isn't seeing at least 13.2V, it shuts off. After a period of time, it cycles back on, and repeats the process. And/or, the input voltage dips below the Input Voltage Lockout Value, and the charger shuts off.
I suspect that under the demand of all accessories pulling on the starter battery/alternator (cooling fans, ECU, headlights, HVAC, etc) that even when you dropped the Shutdown Voltage to 12V, the additional 30-40A load caused a voltage drop that led to charger throttling current and eventually cycling off.
Perhaps this is also the case for when you lowered the Shutdown Voltage to 9V, but I question what the setting of the Input Voltage Lock-Out value is under this scenario (and the 12V Shutdown Voltage scenario above...as either setting would be below the default Input Voltage Lock-Out value, and should cause the charger to stop charging).
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| 66brm wrote: |
| Bodacious wrote: |
| Why not just make a custom set of wires with a Y splice in them. Then you could just run one distributor. |
I don't think electrickery works that way |
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