Running a Pressure Washer.

[cuthound]

If you're using it to prove everything is charging as it should then an error of a few percent won't be important. You'll see if the charging source is working or not plus have a pretty close measurement to boot.

If you're using it to check tail current then an error of a few percent won't be important. If it's stopped dropping then it's stopped dropping.

So for the majority of boaters there is absolutely no need to have it calibrated. A cheap meter would probably drift about with temperature anyway.

Exactly. When I was working it was essential that all test instruments and torque wrenches used for commissioning were calibrated annually, not only for accuracy but also to show an audit trail.

 

For fault finding, instruments were calibrated initially and checked every 5 years unless there was reason to suspect they were out of calibration. Even recalibration every 5 years rarely showed errors of more that 2-3%.

 

For casual use it is not necessary have calibrated instruments.

[hounddog]

I reckon it's worth trying. I ran a 1400 watt pressure washer (Karcher K2) from my 1800 watt inverter on Wednesday this week - it needed it because the boat was covered in a thick layer of dust, mainly bitumen, when it came out of the dry dock and the damp overnight had glued it to the paintwork. I ran the engine (Beta 43 with a 175 amp alternator) at 1300 rpm and at the end of a couple of hours work the boat was clean and the batteries were fully charged.

I ran the smallest Karcher from a Honda EU10i until it melted (the Karcher that is). I don't think that was the fault of the generator.

It was picking up water from a bucket on the roof.

The problem with that is 'false alarms' (which are probably on the 'side of safety') as the voltmeter will only read the voltage at the cigarette lighter socket. If it has been wired with 'thin cable' and is a fair distance from the batteries / fuses then it will suffer volt drop and show a low voltage - it will not show the voltage at the batteries.

Taking a measurement with a DVM will not cause any volt drops because the impedance is so high. Voltage drop is a function of current.

[Chewbacka]

I ran the smallest Karcher from a Honda EU10i until it melted (the Karcher that is). I don't think that was the fault of the generator.

It was picking up water from a bucket on the roof.

 

Taking a measurement with a DVM will not cause any volt drops because the impedance is so high. Voltage drop is a function of current.

True, but if there are a number of items running from the same wire then there could be some volt drop at the volt meter.

If in doubt check battery voltage and cigar socket voltage at the same time, and if they are the same then you can use it - assuming you don't for example have 2 sockets on the one cable and then plug in a load.

[hounddog]

True, but if there are a number of items running from the same wire then there could be some volt drop at the volt meter.

If in doubt check battery voltage and cigar socket voltage at the same time, and if they are the same then you can use it - assuming you don't for example have 2 sockets on the one cable and then plug in a load.

As with anything you have to know what you are doing.

 

Even if you take a reading on the battery if someone's using a hairdryer on the inverter it will tell you very little.

 

As with any voltage reading it will only give the SOC with everything else off. At that point a voltmeter will give the same reading whether in a socket halfway down the boat or straight across the batteries. That's why they are useless for tracing dodgy connections (or checking whether your wiring is too thin)

[Horace42]

Exactly. When I was working it was essential that all test instruments and torque wrenches used for commissioning were calibrated annually, not only for accuracy but also to show an audit trail.

 

For fault finding, instruments were calibrated initially and checked every 5 years unless there was reason to suspect they were out of calibration. Even recalibration every 5 years rarely showed errors of more that 2-3%.

 

For casual use it is not necessary have calibrated instruments.

In terms of the need for accuracy, I can't recall a time I needed it. I recall when I did us my DC clamp meter it was to help identify which cable in amongst a bunch of a dozen or more running along the boat I could use to use feed a new !2v socket I was fitting. Oddly enough the cable I needed to find was not carrying any current.

[Tony Brooks]

Reported