sailorman
Well-Known Member
The Nasa will register .01 amps. i doubt a clamp meter will be that sensitive
How do I measure amps?
- Thread starter Rivers & creeks
- Start date
Bru
Well-Known Member
Exactly
The clamp meters aren't particularly accurate and in a permanent installation it isn't a particularly big deal to install a proper shunt and a couple of wires
I'm suspicious of those incredibly cheap meters off Ebay, I'm really not sure I want a dirt cheap shunt in my domestic battery circuit. Given that around a third or more of the cost of a decent monitor is in the shunt that whole unit is about a third of the price of a good quality shunt on its own
A bargain is a bargain but something that looks way too cheap usually turns out to be a piece of ****!
That's c r a p (a word that is not a swear word in either American English or proper English for crying out loud)
Spyro
Well-Known Member
40amps!!! It shouldn't be.
sailorman
Well-Known Member
Thomas Crapper ( that ok then )
abraxus
Well-Known Member
Personally I don't need accuracy down to a hundredth of an amp. Tenths would be fine, in fact I could even live with rounded up whole amps.
Nor am I concerned about incredibly cheap, just something quick and easy to fit., and so I still don't understand why the cost and bother of a shunt is needed if a clamp ammeter manages without one. Like I said, I have something simillar on my 240v shorepower supply, that took 5 minutes to fit, and so ideally would like something for the dc side, if such a thing exists.
prv
Well-Known Member
It's believable as a fuse spec - a powerful electric ram shoving hard against a wave could probably draw that much briefly - but obviously it won't be pulling anything like that in calm conditions when the OP's crawling around measuring stuff.
(A quick check of the Raymarine manual shows that 40 amps is the recommended fuse for a Type 2 Linear Drive at 12v)
Pete
sailorman
Well-Known Member
Sorry the nasa reads 0ne decimal place
Spyro
Well-Known Member
Ok I take it back then but 40 amps seemed like a very big fuse.
AngusMcDoon
Well-Known Member
It will just be needed by the motor's high starting load which will very quickly drop.
prv
Well-Known Member
Think how hard you sometimes have to shove the helm in a big sea, then imagine you were only given an eight inch tiller to do it with - you'd want 40amp muscles too
Pete
guernseyman
Well-Known Member
A clamp ammeter works like a transformer, treating the clamped wiring as the primary and measuring the current in its own secondary.
halcyon
Well-Known Member
Hall effect, allows measuring DC current and flow.
One thing to consider with a resistance shunt, 500 amp is now commonly used to allow for engine start current, result 500 amp= 50 mV or 0.05 volt, so 1 amp = 0.0001, so 0.1 amp = 0.00001 volt. Now think about contact resistance, inductance from passing power cables, production tolerance and then the problem to convert to a reading.
Brian
JumbleDuck
Well-Known Member
Both. Old and cheap clamp ammeters are the transformer type and measure AC currents only, while the modern sort use Hall effect sensors and do DC as well. Hall effect is much better.
Ten microvolts is tricky. I used to work with a nanovoltmeter, and you can imagine how much worse it gets when you are trying to measure 0.000000001V
JumbleDuck
Well-Known Member
OK, I'll bite. What makes a shunt so expensive?
BERT T
Well-Known Member
The clamp on meter from Maplin is very reasonably priced for one that will measure DC current (my Fluke is around £500) and will be a lot more use around the boat for fault finding.
TQA
Well-Known Member
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Just to complicate matters there is nothing to stop you having more than one ammeter.
I do.
One in the circuit from the solar panels leading into the batteries. Digital - not that it matters.
One in the circuit from the batteries to the domestic items lights fridge A/P etc.
If I relied on the engine for charging much I would add a third in the alternator connection to the battery.
Always good to know what is going on.
I do.
One in the circuit from the solar panels leading into the batteries. Digital - not that it matters.
One in the circuit from the batteries to the domestic items lights fridge A/P etc.
If I relied on the engine for charging much I would add a third in the alternator connection to the battery.
Always good to know what is going on.
Bru
Well-Known Member
Quality!
And accuracy but that's not a major issue in this application
My concerns about a cheap shunt would be the durability of the insulating base and the materials used for the studs and resistor
I doubt it is possible even for the Chinese to make a shunt out of materials that will stand many years of exposure to the atmosphere in the average yacht battery box for £3 :/
Jabs
Well-Known Member
The shunt needs to be hand tweaked to get exactly the correct resistance.
If you look, you will see a saw cut in the 'leaf' that connects the two poles.
This needs to be just right. Too deep and it's scrap!
Tony.
If you look, you will see a saw cut in the 'leaf' that connects the two poles.
This needs to be just right. Too deep and it's scrap!
Tony.
Daydream believer
Well-Known Member
I have a Nasa unit but it is the early version which I am told does 100 amp batteries OK- but might not do 2 connected in parallel
So if I fitted the RS online unit & put the shunt for that in series with the NASA shunt would i be able to still get a reading from both
i could then compare accuracy of both & put one where I can see it on deck
So if I fitted the RS online unit & put the shunt for that in series with the NASA shunt would i be able to still get a reading from both
i could then compare accuracy of both & put one where I can see it on deck
sailorman
Well-Known Member
Its the power that the shunt can handle passing through it, not battery capacity
