Help Understanding House Batteries Charging/Compartment

OK, next "mystery" electrical item.

When I took the access panel off for the charger, mounted just above it, is what appears to be a shunt.

There are two small wires, that from past experience, I would think would run to a monitor to display amps going into, and out of, the battery bank. A much better fuel gauge for batteries then voltage. And, with the shunt already installed, seems trivial to add one, which is great.

Obviously this monitor is not "stock" in the westy, so I am very curious as to what this is attached to, and why the shunt is even installed (but glad it is).....


onemanvan: Once my DC meter arrives I should be able to find the AC charger line and will confirm which one it is.

oldwest: Thanks for the link to those photos, a great addition to this thread. I see only three cables attached to the battery switch. One is from the batteries, one must go to the fuse panel, not sure about the third. Anyone know? As that third cable is even more worrisome if it has no fuse on it. It means an even longer run of unprotected wiring.

Yes - it is that very same shunt that I used for my ammeter ( actually millivolt meter ) to monitor current flowing into/out of the battery bank.

Based on observations and the presence of the shunt I believe the Central Electronics bar graph display is not simply a graphical representation of voltage but 'state of charge'.

Indeed it is not as sophisticated as some state of charge meters. I think it uses some little software algorithm that samples voltage decay with respect to elapsed time given a quantifiable load as determined by the shunt.

I wanted a meter that could measure current into and out of bat's using existing shunt.

Only problem with my solution is one must divide readout by 2 - Westfalia OEM shunt generates 2mv per amp - typical shunt generates 1mv per amp.

The meter I went with is very small and easy to mount - just drill a 7/32" hole and secure with nut from backside.

http://www.amazon.com/Lascar-Electronics-1025S-01-Voltmeter-Digital/dp/B00DDGGDCM

The meter needs an isolated 5v power supply - I chose this one.

http://www.alliedelec.com/recom-power-inc-rs-1205s/70052030/

Since it's so small you can mount it just about anywhere - I mounted mine on the metal plate that the BIG RED switch is mounted on.

John...

Thanks. I agree that the central computer must be using it for the graphs, as nothing else makes much sense. Pretty impressive to be honest in an RV. Typically all you get is a voltage "graph" which is helpful, but not as accurate.

Unlike other James Cook photo linked earlier, this photo of house batteries of a James Cook 4x4 has the same big fat cable with big fuse (now identified by posters as charging from isolator to alternator).

https://4x4westfaliajamescook.files.wordpress.com/2014/11/2007-03-3111-57-34img_2640.jpg

Other wires are for inverter and solar.

One more question.

From what I read online, shunts are normally rated at 50mv, 75mv, or 100mv.

What am I not quite understanding?

I think "typical" 1mv/amp would be 50mv shunt? So what you are saying is the one installed is 100mv shunt?

It would be nice to get a meter that matches the shunt. I'm bad at math .

Maybe it's more complicated then this.

A link I was referencing: http://www.ebay.com/gds/A-Guide-To-Current-Shunts-/10000000001675505/g.html

Quote:

oldwest: Thanks for the link to those photos, a great addition to this thread. I see only three cables attached to the battery switch. One is from the batteries, one must go to the fuse panel, not sure about the third. Anyone know? As that third cable is even more worrisome if it has no fuse on it. It means an even longer run of unprotected wiring.

End Quote.

OneManVan said in other postings that power switch had two terminals, one from batteries and one for loads.

Just guessing: Maybe the two thinner cables on the one terminal both go to the fuseblock. Sometimes, things can't take a big wire or terminal, but can take multiple thinner wires and terminals.

Can't think of any significant 12v loads which bypass the fuseblock (and also turned off by power switch).

Never tried, but can one start generator with 12v power switch off?

Also, with 12v power switch off, does plugged-into shorepower Westy battery charger work to charge batteries?

OldWest said:

Just guessing: Maybe the two thinner cables on the one terminal both go to the fuseblock. Sometimes, things can't take a big wire or terminal, but can take multiple thinner wires and terminals.

Click to expand...

Could be as I don't know of anything else needing a thicker cable either.....

OldWest said:

Never tried, but can one start generator with 12v power switch off?

Click to expand...

For me, yes. Not sure everyone is wired the way mine is though with the generator start cable run directly to the battery.

OldWest said:

Also, with 12v power switch off, does plugged-into shorepower Westy battery charger work to charge batteries?

Click to expand...

Not sure. onemanvan thinks so based on his wiring thoughts. I plan on testing once I get my voltmeter. This might be the third cable on the battery switch also, but it seems a bit thick for a 10A load.

Example:
Let’s say a current shunt is rated at 50 amps, 50mV. This means that when 50 amps is flowing through the shunt, the voltage drop across the shunt will be 50mV. Since the voltage drop is linear in relationship to the current flowing through the shunt, half the current will result in half the voltage drop (at 25 amps, the voltage drop would be 25mV).

However:
The shunt installed in the Westy is not 1mv/amp - I don't know what it's current rating is but let's assume it's 100 amps - as that's what the fuse is rated at. In which case it would be a 100 amp 200mv shunt.

Therefore:
If you don't want to do the math - IE: divide by two - then you'll need to install a 'standard' shunt in series with the existing one...

The meter I installed is - Meter Function: DC Millivolts Meter Range: 0mV to 200mV

John...

Thanks. So I understand that part now.

How do I know what the shunt installed in the Westy is rated at so I can buy an ammeter that registers correctly based on the voltage drop spec?

The meter you had a link for is a volt meter, and you stated there is 2mV difference per amp. This would imply a 100A shunt with 50mv, right?

You wrote: However:
The shunt installed in the Westy is not 1mv/amp - I don't know what it's current rating is but let's assume it's 100 amps - as that's what the fuse is rated at. In which case it would be a 100 amp 200mv shunt.

But that would imply .5mv per amp, no? Confused

And, what fuse? The only 100A fuse I know about is for the combiner/alternator....?

If you put a 5 amp load on the house battery and measure the voltage drop across our shunt you'll get a reading of 10mv. That's how I came up with 2mv/amp.
Ammeters are a combination of a shunt and a volt meter. They're all that way.
We have the shunt - so all we need in addition to that is a properly scaled voltmeter.
The meter I chose is scaled correctly for serving as an ammeter - ie: 0 to 200mv
This combination should work correctly up to 100 amps.
I doubt the flimsy little shunt in our westy's can carry much more than that...

To complete my information on the battery compartment, there were three additional wires bundled with the main cable that goes to the battery switch.

Two are quite small. One a bit bigger.

Not sure what the two small ones are for. Do not appear to be the voltage sensor for the computer as that worked with both disconnected (both wires are attached to same ring terminal so can only remove both at the same time). Also, AC charger worked OK as well, so I don't think they are for that either to detect voltage. Still unknown at this time.

The thicker one (not very thick), is for the AC batter charger. It will charge the batteries regardless of the battery switch since the charged goes direct to the batteries. Since the max is 10A, it being small is not an issue. However it should also have a fuse installed at the battery.

Attached updated photo.

Thank you for all the helpful posts and pictures Kiltym. I hit the road for 5 weeks so have not revisited this issue yet, but will when I return home and address the growing number of maintenance issues.

Robert,

I'd love to see some pictures and a writeup of your van project when you have a chance. I expect it looks quite different than any Westy we're used to.