Main battery ammeter

[nick_the_fish]

Right, i'll start this in a new thread so I don't take over Chris' thread.

I need an ammeter/ voltmeter in the cab to monitor the main battery. I'll stick a Victron type battery monitor on the leisure battery but it seems like overkill to stick this on the main battery.

The plan is to put a shunt next to the battery which everything will run through apart from the winch. This will then allow an ammeter to be safely installed to monitor current.

The question is, how big does the shunt need to be - 50A / 100 A and which ammeter to go for........

(thanks to all the contributions so far from the other thread)

N

 

[Crispin]

How much do you plan on drawing? Once you work that out, then add 20% and you're in good ground. Not sure if putting a shunt on the main down to the starter though. That could be many more amps.

I have a number of battery / inverter setups at home, one has a 10A shunt, one a 50A and one a 300A shunt. They all get used to around 80/90% of rated. If you go too big then you lose resolution. Putting a 300A shunt on when you only needed a 20A and you'll probably not see low-draw readinsg.

I buy the shunts off fleabay - http://www.ebay.co.uk/sch/i.html?_f....H0.X100A+shunt.TRS0&_nkw=100A+shunt&_sacat=0
Never had a problem with them, the ones that I have managed to test are pretty accurate to within reason.

 

[Chris]

Well hating to state the obvious but the Victron is expandable and you can get a kit that monitors the second battery.

 

[StarCruiser]

It's a bit chicken and egg to see how much current is drawn, you need an ammeter in circuit (or measure with a DC clamp meter). I would say to avoid putting the shunt in series with the starter and that 100A sounds the smallest I would fit. However, I would want to measure it first to make sure the shunt is oversized. I dare say they will take a short time overload anyway. Is yours 12v start or 24v?

 

[Crispin]

It's a bit chicken and egg to see how much current is drawn

What's the main fuse in the distribution box? Get the next highest one to that.

 

[StarCruiser]

What's the main fuse in the distribution box? Get the next highest one to that.

That would be a good easy way but sometimes there are several main fuses, or like the 80s, fusible links.

 

[Crispin]

Out of interest - do you know if a cheap(ish) tong-tester which works on DC? I know they're out there but often cost the earth...

 

[Chris]

The 80 has a sub fuse box drawn directly from the battery supply. Would that work?

 

[nick_the_fish]

Thanks guys - Loads of really great advise as normal. It really is very much appreciated.

Its worth noting electrical stuff its my strong point so bear with me.....

Its a 105 series so 12v.

My understanding of what needs to happen is:

1. Winch and starter both connected directly to battery
2. Fuse box and alternator through the shunt
3. Shunt to be sized appropriately

at which point I hit a wall. How do I calculate how much current i'm going to draw? I've got all the extras (fridge/ lighting etc) off the aux battery so only the vehicle stuff off the main battery - headlights/ wipers/ blowers/ stereo etc but none of them have power ratings.

There is a main fuse box in the engine bay and a sub-fuse box in the least accessible place on earth by the passenger feet. Presumable the fuse-box comes off a larger fuse in the main fuse box (?). I'lll have a look at the largest fuse in there and make sure the shunt is larger than that.

Then is on to e-bay for a shunt.

Now will a cheap ammeter (there are loads on e-bay) be accurate do you think? are they particularly sophisticated bits of kit?

N

 

[StarCruiser]

Sounds fine, though I'm not sure on the wiring for a 105. The ammeters on eBay should all be reasonable, after all you're not after laboratory precision, if you're worried about longevity, buy a couple of them- they're cheap enough.