Where are my volts going?

Veloman

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I have a fairly standard electrical set up for the habitation side of my camper. !00Ah battery, a Victron 75/15 mppt controller and a BM1 battery monitor. It works fine and I'm happy with it except that I noticed the BM1 was showing battery voltage at 13.6 volts towards the end of the day. I checked that the Victron was in float mode as expected given that I hadn't used the van that day and that the float voltage in settings was set to 13.8 volts which was the voltage I expected to see on the BM1. I checked the voltage at the battery with a voltmeter and sure enough it was 13.6 volts.
I then increased the float voltage setting in the Victron to 14 volts and both BM1 and measured battery voltage rose to 13.8 volts.
Where is my 0.2 volts going? Should I leave the Victron float voltage set to 14 volts? Does it matter?
 
13.6 to 13.8 is a float, should hit 14.4 when o full charge, either from charger or solar, but all go to sleep at night with solar and can go down to 12.7 ish.
 
The difference between 13.6 and 13.8 is about what I'd expect if there was a diode in one of the measuring circuits.
 
maingate said:
Did you put a test meter over the battery terminals? 0.2V loss in the wiring is not unusual.
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Yes 13.6 volts measured at battery terminals when Victron is set for 13.8 volts. The Victron wiring from battery is about 3 feet of reasonably substantial automotive cable (sorry not sure of diameter etc). I guess my question is - should I adjust the Victron float voltage setting such that I read 13.8 volts at the battery as this seems to be considered to be the optimum float voltage? This would presumably nullify any cable loss? Does it really matter? I just want to make sure my battery is charged to its maximum when I have the opportunity to do so. Thanks for your replies.
 
Anything from about 13.6 to 13.8 is normal, standing battery volts is 12.7 on newish batts, 14.4 on full alt charging but may drop back to 14.2
 
Geek said:
When the battery is full, the alternator should drop back to 13.7 or so.

If the alternator is putting out 14.2 it doesn't think the battery is full yet.
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In 40 odd years of working on cars/vans all stayed at 14.3/4 volts when running, both my van and car do, its the current/amps that drop back.
 
trevskoda said:
In 40 odd years of working on cars/vans all stayed at 14.3/4 volts when running, both my van and car do, its the current/amps that drop back.
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Well, that's not how it should be. Both my car and my motorhome drop the voltage back when the battery is full. Perhaps yours never get to that point: it can take a few hours sometimes
 
Geek said:
Well, that's not how it should be. Both my car and my motorhome drop the voltage back when the battery is full. Perhaps yours never get to that point: it can take a few hours sometimes
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No you have a smart altenator which works that way, older stuff does not, its the current/amps that are cut back.
Voltage of engine batt right, service batts on left.
dash voltage .jpg
 
Smart alternators (which I don't have) don't work that way at all.

That photo suggests that you don't have a b2b charger, so it's very likely that your batteries will never reach fully charged.
 
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