Issue with battery monitor and solar?

[jviss]

I just purchased a Victron BMV-600 batter monitor, and a Morningstar SS-10-12V charge controller for my 51 Watt solar panel.

In the BMV manual it states:

In case of a 12 V battery, the BMV resets to “fully charged” when the following
“charged parameters” are met: the voltage exceeds 13.2 V and
simultaneously the (tail-) charge current is less than 4.0 % of the total
battery capacity (e.g. 8 A for a 200 Ah battery) during 4 minutes.

What will happen when my solar panel is the sole charging source, and is putting approximately 3.75A into my 300AH house bank, at, say 13.6V. Will the BMV think that the house bank is fully charged?

The BMV seems to assume that the charge current limit is imposed by the sink, i.e., batteries, not the source, a limited capacity solar array.

Comments?

 

[Stu Jackson]

Those are defaults and can be and should be changed.

Try this:

For everyone installing a battery monitor: The "Gotcha Algorithm" thread, a "MUST READ"

http://c34.org/bbs/index.php/topic,4922.0.html

DEFAULTS are factory settings that are made to be modified to suit your setup.

 

[Maine Sail]

I just purchased a Victron BMV-600 batter monitor, and a Morningstar SS-10-12V charge controller for my 51 Watt solar panel.

In the BMV manual it states:



What will happen when my solar panel is the sole charging source, and is putting approximately 3.75A into my 300AH house bank, at, say 13.6V. Will the BMV think that the house bank is fully charged?

The BMV seems to assume that the charge current limit is imposed by the sink, i.e., batteries, not the source, a limited capacity solar array.

Comments?

You can change the 4% to 1% or less if you need to... As always sync the monitor manually when the accepted current is below 2% of bank acceptance.

 

[jviss]

You can change the 4% to 1% or less if you need to... As always sync the monitor manually when the accepted current is below 2% of bank acceptance.

Thanks for the reply. Not sure I get it though. What if the available current, e.g., from a solar panel, is less that what the bank could absorb?

 

[Maine Sail]

Thanks for the reply. Not sure I get it though. What if the available current, e.g., from a solar panel, is less that what the bank could absorb?

You fire up the motor with no loads on and check the accepted current after the initial in-rush current winds back. If that current is below about 2% of bank capacity simply do a manual sync.. Solar panels can trick monitors into re-setting despite the bank not necessarily being full.

 

[jviss]

You fire up the motor with no loads on and check the accepted current after the initial in-rush current winds back. If that current is below about 2% of bank capacity simply do a manual sync.. Solar panels can trick monitors into re-setting despite the bank not necessarily being full.

O.K., got it, thanks. That's a bit disappointing, though. I didn't anticipate that. It means that the there's a built-in assumption, in the design of this kind of battery monitor, that the charging energy available, when charging, will always be more than what the batteries can accept; i.e., that the batteries' acceptance is the limit to charging. So, when you go back to the boat after a few days, you won't know if the batteries are fully charged via solar, and you have to fire up the engine, observe the the current 'tail,' and manually resynch. Bummer.

Thinking more about this, it occurs to me that the setting sun could produce, from the solar panel, just the kind of tapering that the monitor thinks is the result of a large charging source and full batteries.

I guess this could also happen with the engine idling, too. At idle, my alternator isn't spinning fast enough to get the voltage up high enough to charge the batteries well. For example, my recollection is that at idle I generate about 13.5V. I can't recall ever having measured the charging current at idle with varying battery states of charge, but I can imagine that the current might be low enough, i.e., below 4% (or 2%) of capacity, which would fool the monitor into thinking the batteries were fully charged. Here's the scenario: batteries at half capacity. Start engine, idle (to warm up), charging voltage present 13.5V, current below 12 Amps (for a 300AH bank); after 4 minutes of this condition, the monitor decides the batteries are full.

Caveat: I haven't fully studied the monitor manual yet, and I know that the "charged-paramters" (Vc, It, Tcd) are adjustable; so, I may be able to program around these issues.

Here's the monitor manual for those who care to speculate on this:
http://www.victronenergy.com/upload/documents/Manual%20-%20BMV%20-%20600S%20600HS%20602S%20-%20rev%2014%20-%20EN%20NL%20FR%20DE%20ES%20IT%20PT%20SE.pdf

 

[Stu Jackson]

jviss, the reason we sent you the Gotcha is to help you avoid reinventing the wheel. Your issue is exactly what that "premature full" discussion is all about. Many folks have had some difficulty getting their heads around it. The discussion about "do the math" is the key, specially if your fridge is running.

My M25 at idle does what you suggest in terms of alternator output. Raise it up to 1,500 rpm and the voltage goes up.

You might want to install it and try it out instead of over-thinking it.

In addition, Maine Sail has noted many times before (although you may not have been reading those posts because you hadn't gotten a monitor yet) that he recommends resynching anyway when he knows the bank is full.

Since you are not using the monitor to control anything, like I am with my Link 2000 and Freedom 15, it's really less of an issue for you.

All the algorithms are similar, so if your manual is hard to understand, download, as suggested, the Link 2000 manual, which is somewhat better written although, as mentioned in the Gotcha, none of this is really very clear. That's why we wrote the Gotcha and continue to reference it.

Good luck, you'll simply love your monitor.

Had this kinda discussion on another forum:

You wrote: Don't let the poor choice of the Links default values put you off.

I don't at all. I don't think they're a poor choice at all. They are simply a default, mean to be modified based on your (house) bank size and the gadgets you have on your boat. Heck, if we didn't have a fridge, and had a 200 ah house bank, and no Freedom 15 I/C, there wouldn't be a need to modify anything. As I suggested earlier and in the algorithm topic, you simply have to "do the math" to find out what works for you.

Years ago, when programming first became available on mainframe computers (heck, 'member those days?!?) the program used to calculate the air quantities didn't make sense to me, 'cuz they were wrong when i did it by hand. When I talked to the programmer he said: "Oh, those are just the default values." I said, "Sure and they only work in one city in the entire USA, what happens when you are in a different city?" "Oh, you change the parameters." "Right, fella, but where have you bothered to tell anyone about this little gem?!?"

Defaults, the curse of unknowing engineers and sailors!

The issue remains, of course, declaration of prematurely full.

Your boat, your monitor, your choice, but I gotta tell ya that 99% of people installing battery monitors, professionally or personally, don't have a clue about these features.

Thanks for listening.

Stu

 

[jviss]

Stu,

Thanks. I'll read the stuff you reference.

jv

 

[jviss]

I read all the referenced material, Stu, thanks.

I have a question about the refrigerator scenario. Does this happen when you are using the shore power charger? What's the output capacity of that charger?

Thanks,

jv