Strange B2B behaviour/ power drain

You have a Victron Orion XS DC-DC charger (B2B). In photo 0943 it says it is in the Bulk charge mode. Its input is 13.3V 50A from the alternator, which is the maximum amps for an Orion XS. The power (watts) taken from the alternator is 13.3 x 50.0 = 665W.

The B2B output is 13.8V 47.1A. The B2B pushes out the maximum amps that is capable of, as the battery voltage gradually rises. Here it has reached 13.8V. The power output (watts) from the B2B is 13.8 x 47.1 = 652W. You can see that there is a bit of power lost inside the B2B as it converts the voltage. 665W - 652W = 13W. As a percentage that's (13 / 665) x 100 = 2 percent, so very efficient.

The output voltage should gradually rise as the battery fills up. If it's lithium, when it reaches the 'absorption voltage' it's probably supposed to just stop charging. The voltage will remain at about the absorption voltage (14.1V), and the amps will drop to zero. So the snapshot of photo 0944 is correct.

The 'absorption voltage' and 'float voltage' are not relevant for lithium batteries, they are a relic from lead-acid battery charging profiles. For a lithium battery, the important quantity is the voltage that shows the battery is full, when the charger cuts off. If you had a charger that was designed only for lithium batteries, you would call that voltage the 'Cutoff Voltage'. But since the charger can do both lead-acid and lithium, they keep the old name of 'Absorption voltage'. Even though a lithium battery doesn't require an absorption stage, and doesn't require float charging.
 
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Lenny HB said:
Fogstar recommend 14.2v for charging with Victron equipment (used to be 14.1).
I have mine set at 14.25 as some people have had problems with them not getting to 100% at 14.2v.
Float voltage should be 13.5v as the battery won't take a charge at that voltage and you shouldn't float Lithium's.
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In my case I started off at 14.2v but the B2B was not fully charging the battery, I then went to 14.25 and ultimately ended up at 14.3v before it worked as expected, also remember that the B2B doesn't get actual battery voltage from the shunt so 14.3v output is likely to be a bit less at the battery. In the case of the float voltage I have a CBE battery maintainer for the starter battery and that requires over 13.6v to work, so i'm hoping the extra 0.11v doesn't take too much off the life of the battery.
 
StillGoing said:
Why don’t you use D+ to control the B2B? It’s much more reliable.
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If you got it? Yes that would be my preferred option as well, instead of the engine detection.
 
ChrisL said:
In my case I started off at 14.2v but the B2B was not fully charging the battery, I then went to 14.25 and ultimately ended up at 14.3v before it worked as expected, also remember that the B2B doesn't get actual battery voltage from the shunt so 14.3v output is likely to be a bit less at the battery. In the case of the float voltage I have a CBE battery maintainer for the starter battery and that requires over 13.6v to work, so i'm hoping the extra 0.11v doesn't take too much off the life of the battery.
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My solar chargers are set at 14.05v with 13.5v float. Anything above this you will try to squeeze another 2-3Ah into a 300-500Ah battery. Why? My thinking is, I you have a pretty good large capacity, don't try to push in the last 3-4Ah into the battery, and keep it pinned at high voltage for too long.
Just a thought.

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Here's another question, I have recently fitted this shunt, does the photo suggest that something it draining the engine battery, there is nothing switched on.



IMG_0953.webp
 
Hymerboy said:
Here's another question, I have recently fitted this shunt, does the photo suggest that something it draining the engine battery, there is nothing switched on.



View attachment 1001641
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In most vehicles there will be a small drain on the starter battery from a constant power feed to the stereo, alarm etc. You can measure how much of a drain you have using a DC clamp meter on the starter battery earth lead, in addition to the above items a faulty diode in your alternator can also cause a drain on the battery.
 
12.54v is a bit low two questions, how long since the starter battery had a charge & do you have a smart alternator?
 
The only information that shunt display shows about the starter battery is the voltage. It's 12.54V, which is not quite fully charged but not particularly low. About par for the course if you have a smart alternator that doesn't ever fully charge the starter battery.

The other information (13.66V, -0.13A) is for the leisure battery, which presumably is a lithium, and there is a small drain of 130mA. That's not particularly high for a motorhome, although if it was a car it would be regarded as a drain fault requiring investigation.

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Lenny HB said:
12.54v is a bit low two questions, how long since the starter battery had a charge & do you have a smart alternator?
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I took the van out for a run to York about 1hr 15mins on Tuesday, the shunt reading was over 13 v. I dont think I have a smart alternator although I dont know how to tell. its a 2013 Hymer 680
 
2013 it will be a standard alternator.
Can you put mains on and get the starter battery fully charged then monitor it to see how fast the voltage drops.
Get it fully charged then disconnect the charging and check it after an hour then monitor it daily.

I'm assuming you don't have a DC clamp meter.
 
Lenny HB said:
2013 it will be a standard alternator.
Can you put mains on and get the starter battery fully charged then monitor it to see how fast the voltage drops.
Get it fully charged then disconnect the charging and check it after an hour then monitor it daily.

I'm assuming you don't have a DC clamp meter.
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Will do thanks, I do have a new DC clamp meter, just need to work out how to use it.
 
autorouter said:
You have a Victron Orion XS DC-DC charger (B2B). In photo 0943 it says it is in the Bulk charge mode. Its input is 13.3V 50A from the alternator, which is the maximum amps for an Orion XS. The power (watts) taken from the alternator is 13.3 x 50.0 = 665W.

The B2B output is 13.8V 47.1A. The B2B pushes out the maximum amps that is capable of, as the battery voltage gradually rises. Here it has reached 13.8V. The power output (watts) from the B2B is 13.8 x 47.1 = 652W. You can see that there is a bit of power lost inside the B2B as it converts the voltage. 665W - 652W = 13W. As a percentage that's (13 / 665) x 100 = 2 percent, so very efficient.

The output voltage should gradually rise as the battery fills up. If it's lithium, when it reaches the 'absorption voltage' it's probably supposed to just stop charging. The voltage will remain at about the absorption voltage (14.1V), and the amps will drop to zero. So the snapshot of photo 0944 is correct.

The 'absorption voltage' and 'float voltage' are not relevant for lithium batteries, they are a relic from lead-acid battery charging profiles. For a lithium battery, the important quantity is the voltage that shows the battery is full, when the charger cuts off. If you had a charger that was designed only for lithium batteries, you would call that voltage the 'Cutoff Voltage'. But since the charger can do both lead-acid and lithium, they keep the old name of 'Absorption voltage'. Even though a lithium battery doesn't require an absorption stage, and doesn't require float charging.
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Hi Autorouter, I have just read your answer, My B2B only seems to go to bulk so it seems that it is doing ok ?
 
ChrisL said:
Why do they seem odd? the B2B is putting out 47 amps, the shunt is telling you that 36 amps are going into the battery, the difference is being consumed by something else, most likely the fridge I would think? Depending on how your system is wired.
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Hi ChrisL
Last night my engine battery reading was 13.86v and this morning it was 12v does this indicate a drain or is it normal ?
Jack.

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Hymerboy said:
Hi ChrisL
Last night my engine battery reading was 13.86v and this morning it was 12v does this indicate a drain or is it normal ?
Jack.
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No that's not normal unless something is draining the battery or it is on its last legs.
 
ChrisL said:
No that's not normal unless something is draining the battery or it is on its last legs.
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Hi Chrisl,
I have just taken two readings with the multimeter on the mppt, one with the solar fuse removed from the EBL and one with it in, :- fuse in Batt 12.77, Pv 17.6. Fuse out + 14.30, PV 1.00.
It's now 3.30 pm I've just taken a reading from the shunt as, follows Leisure Battery 12.74, Engine Battery 12.28 and we've had full sun all day on the solar panel, obviously something amiss, I need to find out how to tell whether it's the battery or a drain.
Jack
 
Hymerboy said:
Hi Chrisl,
I have just taken two readings with the multimeter on the mppt, one with the solar fuse removed from the EBL and one with it in, :- fuse in Batt 12.77, Pv 17.6. Fuse out + 14.30, PV 1.00.
It's now 3.30 pm I've just taken a reading from the shunt as, follows Leisure Battery 12.74, Engine Battery 12.28 and we've had full sun all day on the solar panel, obviously something amiss, I need to find out how to tell whether it's the battery or a drain.
Jack
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You need to use a DC clamp meter on the earth lead of the engine battery to measure the current being discharged, with everything turned off, on a modern vehicle it may be between 50 and 85 milliamps on an older vehicle less then 50 milliamps, you need to make sure the clamp meter can measure DC amps in the milliamps range. The meter will also tell you if your starter battery is being charged when a charging source is in operation.
 
ChrisL said:
You need to use a DC clamp meter on the earth lead of the engine battery to measure the current being discharged, with everything turned off, on a modern vehicle it may be between 50 and 85 milliamps on an older vehicle less then 50 milliamps, you need to make sure the clamp meter can measure DC amps in the milliamps range. The meter will also tell you if your starter battery is being charged when a charging source is in operation.
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Just one more thing if you don't mind, what setting should the clamp meter be on to see if it is being charged
 
Hymerboy said:
Just one more thing if you don't mind, what setting should the clamp meter be on to see if it is being charged
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If you're checking for charging I would set it as below, or maybe on the 20 amp range, if you're checking for parasitic drain with everything turned off I would set it at the 2 amp range, my meter can measure a/c and dc amps so as well as the range setting I have to set it to dc with the blue button.

20250417_190233.webp

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ChrisL said:
If you're checking for charging I would set it as below, or maybe on the 20 amp range, if you're checking for parasitic drain with everything turned off I would set it at the 2 amp range, my meter can measure a/c and dc amps so as well as the range setting I have to set it to dc with the blue button.

View attachment 1044949
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Im ever so gratefull for your help thanks.
Jack.
 
Hymerboy said:
Im ever so gratefull for your help thanks.
Jack.
Click to expand...
No worries, this video may help although the meter he uses is not reliable at very low current, mine is, several of us use the meter in my photo as they are reliable and quite accurate at a reasonable cost.

 

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