Help with split-charge setup and ammeter DC


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Old 02-01-16, 12:31 PM
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Help with split-charge setup and ammeter DC

Hi I hope there are people who can point me in the right direction. Im planning a small project and want to be sure Im not making any stupid mistakes.

I have a window cleaning van and would like to beef up & tidy the aux electrics.
It has a new 110ah budget hancock leisure battery and a decent VSR.

Part of this project is to install a dual voltmeter and ammeter to measure the current voltage level and amps being drawn from the aux battery. Ive bought the volt/amp meter and 100A 75mv shunt.

I have bodged in into the current setup and all seems to be working, the current setup is..
- voltmeter/ammeter display powered by a 9v battery
- Shunt between aux battery neg and a common ground post which most aux devices are connected to.
The only issue ive noticed is the ammeter reads 0 when the van is running and split charge relay is open. (Not an issue)

I cant help scratching my head and thinking ive got it wrong though, my main concern is where to put the shunt and can I ground devices served by the aux battery straight to the chassis and still see a true reading of amps being drawn from the aux battery? . Any wisdom would be appreciated.


on a side note, i would like to supply the display using a dc-dc isolated contraption, but can only seem to find board-mount chip like devices. My fat fingers will do nothing but crush such a thing so could someone point me towards a dc-dc isolated supply contraption with either screw or spade terminals?
 
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Old 02-01-16, 05:41 PM
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Welcome to the forums.

can I ground devices served by the aux battery straight to the chassis and still see a true reading of amps being drawn from the aux battery?
Yes.....as long as the aux battery is connected to chassis ground.

my main concern is where to put the shunt
The shunt and ammeter are ALWAYS connected together in parallel. The shunt can go in the positive or negative line..... it doesn't make a difference as long as you get the meter polarity correct. The meter has polarity. The shunt does not.

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I'm guessing these meters are those digital ones that require a separate DC supply to run them ?
I bought a case of the LED voltmeters for vehicles but dumped them as they also required a DC/DC supply.

You better sit down when you see the cost for a 12vdc to 12vdc isolated supply. Part # ZUW251212 is one that I've used in the past. ZUW251212 Cosel | Mouser
 
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Old 02-02-16, 12:32 PM
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Thank you for your reply.

I should have posted the link originally... I bought one of these

Not technically an ammeter but a voltmeter which converts to amps (apparently) Does that make a difference to where it should be installed?



re the isolated supply for the display.. would this do the job?

This is all a bit over my head


edit: is worth saying its installed in current setup and working (seemingly) perfectly. It reads 4-7 amps with 2 pumps running which is exactly what I would expect.


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Last edited by WindowCleanBill; 02-02-16 at 01:01 PM.
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Old 02-02-16, 01:54 PM
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OR, buy the Blue Seas M-ACR.

If I get the gist of this mission, it's to allow you to supply lots of 12V energy without leaving the van with a dead starting battery??

There are lots of frills with the system diagram. Who is watching the ammeter/voltmeter? What is the time delay relay for? I see no real need for the DC to DC converter, especially an isolated one.

This same kind of system is used on zillions of boats that want a house battery, but have only a single engine.
 
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Old 02-02-16, 03:03 PM
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There is no real need for the frills, but I want it to be as good as it can be.

The timer... is actually a programmable timer switch, the main purpose is to shut the aux circuits down at night in case anything has been left on.

The Display... 99% of the time no-one will be watching it! but I like it and for the price why not?

The dc-dc converter... Apparently required for the readings to be accurate. I can confirm that as powering it from either battery gives silly readings. Powered by a 9v square battery it works perfectly.
 
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Old 02-02-16, 04:56 PM
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This line of digital monitors require an isolated 12VDC supply to run the electronics. It makes for a lower cost (ie:cheap) meter up front but the DC-DC supply is costly.

I mentioned I dumped a whole box of voltmeters for just that reason.

The supply you linked to will not work. That supply requires 18vdc minimum which you don't have.
 
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Old 02-03-16, 12:48 AM
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Sorry about that PJ, I was going to link to one like this . There are loads of them on ebay but the price difference from what you suggested tells me Im looking at the wrong things. Please let me know whether something like that would work (using a jumper ribbon or solder to connect).

Thanks again
 
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Old 02-03-16, 10:10 AM
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I think im happy with how and where to install the shunt. The only benefit I can see having it on the positive side, is that the meter also needs a link to positive side for voltage measuring so would keep cables tidy.

The dc-dc converter is the loose end now. The display/meter doesn't require 12v from what I can see. it requires 4-30v and draws next to nothing... would one of the cheap board mount converters (10-16v in / 5v 1w out) work? (link in prev post)
Would like to get one ordered asap if all looks right
 
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Old 02-03-16, 10:29 AM
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That should work. You won't know for sure until you try it. It's maximum output is 200ma. Not sure what the meter requires.
 
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Old 02-07-16, 11:00 AM
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I found a dc-dc converter that puts out a bit more power and am just waiting for that to arrive. Other than that all done(display still on 9v battery).
For your approval / flaming...
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Im quite happy with it.. better than the bodge that was there before!
 
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Old 02-07-16, 11:13 AM
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Flames aren't tolerated here.

Looks pretty neat. Can't see much detail in the wiring.
I had expected to see at least #8 to the shunt and fuse panel.
 
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Old 02-07-16, 11:22 AM
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The wire going to the fuse box is huge! no idea what guage though. The neg side wire is rated 30a but when I fit the converter Ill double/triple it up while im there. I dont yet understand wire gauge numbers but everything (bar that particular section!) should be overkill.

Most that'll ever be drawn in current system is 2 x water pumps, 2 x recovery beacons, 2 x internal lights and 2 fans. so about 20 amps? but yes that section of the circuit (around shunt) wants beefing up
 
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Old 02-07-16, 11:47 AM
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Just to touch on a couple of points. One of my specialties was/is automotive electronics and when I had my store I'd see many melted wiring problems as well as a few fires because people don't realize the power of a battery.... and two batteries in parallel is well over 1000amps.

The hot wire between your aux system and the vehicle must be protected at both ends by a fuse. A short anywhere on that wire with no fuses would be catastrophic.

In auto use.....
#18 = +/-5A
#16 = +/-10A
#14 = +/-15A
#12 = +/-20A
#10 = +/-25A
#8 = +/-40A
 
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Old 02-07-16, 12:34 PM
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All understood, its fused at the van battery end so will add a decent fuse in the box. The cable is rated 40a and fuse is 20a (i believe). The cable between van battery and vsr is routed internally and in its own conduit all the way.

Thanks for all advice, ill update when converter arrives and ive made the few changes discussed.
 
 

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