Current Shunt - What size?

[GordMay]

The shunt current rating indicates the current that produces a full scale reading on the associated meter.
Continuous currents should not exceed 80% of the shunt rating.
However, short term currents that occur in motor-starting or engine-cranking can exceed the shunt rating by a factor of 2 or more without damage to the shunt or meter.

[john61ct]

If all you want to do is measure small loads, then just put the shunt from a small inexpensive AH counter in between the bank and the loads you want to measure, bypassing the larger loads.

You only need the larger shunt if you are metering all in- and output for the bank as a whole, trying to track SoC.

[a64pilot]

Originally Posted by Jim Cate

IMO, certainly OK. Realistically, short term overcurrents will not hurt anything at all, so don't fret about it. Having the higher resolution measurements available with a lower range shunt on the other hand will be useful in tracking individual consumers.

Jim

Smaller shunt for higher resolution is certainly logical. Always taught to use any measuring device where the measurement was in the middle third of its scale.
However to my amazement, my 500 amp shunt will accurately measure currents to less than an amp. It’s important to me cause I use the shunt to determine when to trip the charger to float, which is when the bank is accepting less than 3 amps.
I have verified the accuracy with my calibrated Fluke multimeter.

However I think keeping the connections to the shunt clean and absolutely corrosion free is most important.

[Bill Seal]

Most of the cheap panel ammeters on Ebay do not measure negative current flow (charging). I haven't figured out how to tell which ones do.

[john61ct]

eBay guarantee is great for buyers, message the sellar and ask.

If not as represented, you get a full refund, and since they also have to pay the return shipping, they'll often say just keep it free.

[john61ct]

Also sometimes you can find a user manual online; this one is commonly used by RC hobbyists

https://m.ebay.com/itm/G-T-POWER-Wat...W/222720679665

[smac999]

Originally Posted by Bill Seal

Most of the cheap panel ammeters on Ebay do not measure negative current flow (charging). I haven't figured out how to tell which ones do.

you can measure the pos or neg wire. the current will obviosly be the same in both wires. it makes no difference. if pos you then have to fuse the 2 data cables though as well leaving the shunt. it's just safer measuring the neg which is why it's more common.

[john61ct]

No he means some meters only measure current "flow" in one direction. Have to choose either loads or charging with a single unit, or use two in the same spot.

While the more sophisticated ones like proper battery SoC monitors are "two way" show the net result when +charging and -loads are concurrent, when loads > charging displays a negative amps reading.

[smac999]

ah. some analog gauges will have 0 in middle and go both ways.

for ~$200 I'd just buy a victon 700 and forget the cheap stuff.

[john61ct]

Yes as a full BM, 712 for me, after a SmartGauge.

https://www.victronenergy.com/blog/2...ooth-built-in/

But the cheap **AH counting** ones are good for metering specific devices or circuits in isolation for troubleshooting. Andersons can basically make any such into a portable tool.

[CatNewBee]

You have to chose your shunt according to your expected max power consumption. A good indicator is your used fuse rating of the batteries.
Let's say you have 3 12V batteries in parallel and each has a füse of 100A on its terminal, the maximum current from / to the battery will be limited to 300A, so a shunt with 500A is more than sufficient. (This is the standard shunt supplied by Victron with their BMV monitors)

If you have large inverter/charger and LFP batteries, where the inverter alone can draw up to 500A, you can install a higher rated shunt (e.g. 1000A), if you have a small bank (1 or 2 12V AGM batteries, small or no inverter), a much smaller shunt could be appropriate, so you will get a higher resolution on small currents.

The shunt should match your installation load design. It makes no sense to go too big, but the shunt should be able to handle the maximum allowed load easily.

[Zil]

I installed a victron monitor. My choice was either 50 or 500 amp shunt. Charger is 60 amps, microwave draws 150 amps.

[jbinbi]

To the OP, I am not sure if you have an inverter. I have a Lagoon, same manuf parts as Beneteau. It has 3 160AH house bank, and was just told that the shunt is 100A 50mv. See this thread for pics.

http://www.cruisersforum.com/forums/...-a-200569.html

[john61ct]

Originally Posted by Zil

I installed a victron monitor. My choice was either 50 or 500 amp shunt. Charger is 60 amps, microwave draws 150 amps.

My understanding is that modern Victron BMs are adjustable enough so that they can be used with just about any shunt.

Other brands even if you can adjust the size in amps, require a certain mV spec.

[CatNewBee]

Originally Posted by jbinbi

To the OP, I am not sure if you have an inverter. I have a Lagoon, same manuf parts as Beneteau. It has 3 160AH house bank, and was just told that the shunt is 100A 50mv. See this thread for pics.

http://www.cruisersforum.com/forums/...-a-200569.html

Actually, the newer Lagoons have often two shunts, the shunt for the switch panel (measures 12V consumption of the on-board electronics only, Voltage and Amps display) and a master shunt with panel (Mastervolt, 250A), that measures the battery bank, the currents in and out, the SOC and violations (deep discharge, overcharge, over-current) on the batteries for warranty claims.

Some Lagoons have an inverter pre-installed (in the L400 it is in the port aft cabin behind the wall panel on the right, the remote switch for it is located next to the shore power selector switch port hull midships ).