colind3782
Well-known member
Just make sure the clamp meter you order does DC current as well as AC. It’s often not immediately obvious.
battery dimensioning basics....
- Thread starter vasant
- Start date
Refueler
Well-known member
Be wary of many Clamp meters ... as I have found out to my cost and checking with others who have bought other brands ............ The clamp part works fine with AC ... but the DC needs leads attached and works like a normal multi-meter .... clamps don't work.
KompetentKrew
Well-known member
Perhaps that's why I found mine to be rubbish.
lustyd
Well-known member
clamps work fine with DC as long as you get a DC capable one.
Refueler
Well-known member
That's what I thought .... [aid out on a Clamp Meter advertised to do DC via clamp ..... arrived .... no way.
Spoke to others with clamps and 3 out of the 5 asked said they found the same ...
They needed the leads plugged and use as a multi-meter.
I have been looking for a real deal since ...
rogerthebodger
Well-known member
DC current clamp meters also need to be zeroed out and can and drift when measuring DC current with a clamp meter
PaulRainbow
Well-known member
lustyd
Well-known member
unfortunately you fell for the same "scam" I did. Yes, it's a clamp meter and yes it's a DC meter, but it's not a DC Clamp Meter. Unfortunately you have to be more careful when ordering these as others have said.
Here's the one I have https://www.amazon.co.uk/UNI-T-Resistance-Capacitance-Multimeter-Temperature/dp/B00O1Q2HOQ
PaulRainbow
Well-known member
This is all too often the case with el cheapo ones on the likes of Ebay.
lustyd
Well-known member
I should probably clarify that I put scam in quotes as they do exactly what they say and seem accurate enough so for the lower price they're probably great for some folk. I felt tricked but in theory it was my fault
colind3782
Well-known member
Don’t ask me how I know!
andsarkit
Well-known member
Clamp meters are not good for measuring just a few amps and usually have a range a several hundred amps. You can get low range ones from the likes of Fluke but they also measure the earth's magnetic field quite well. You have to zero them in the orientation of the measurement and take the reading without moving the clamp angle to the earths field. It is possible to read down to tens of milliamps with these meters. I have found standard DC clamp meters very useful especially if they have a peak hold function to catch a short duration peak current
Back to the original question. The compressor motor can momentarily draw five to ten times the running current when starting up. The combination of battery internal resistance. cable resistance, switch resistance, fuse resistance and connection resistance could be enough to drop the voltage to the drop out value and prevent the motor ever starting. Oversize cables and clean connections might just be enough to get the motor through the the starting surge current.
Back to the original question. The compressor motor can momentarily draw five to ten times the running current when starting up. The combination of battery internal resistance. cable resistance, switch resistance, fuse resistance and connection resistance could be enough to drop the voltage to the drop out value and prevent the motor ever starting. Oversize cables and clean connections might just be enough to get the motor through the the starting surge current.
ChromeDome
Well-known member
I only have one. Works fine for my needs (boat, cars, house). BTW not el cheapo.
PaulRainbow
Well-known member
Both of mine have 40a and 400a ranges and will measure down to fractions of an amp.
Zing
Well-known member
Actually most clamp on meters don’t measure low currents well, typically a few tens of milliamperes and lower, so if you have a very low current mysterious parasitic type loss to diagnose you will need to use a regular in-series ammeter.
vasant
Member
Hi there i am back after some time.
So i did today a more seroius test. Battery fully charged (was one month idle with 50W solar panel connected) showed 13.8.
All other pplianced shut off.
So the fridge ran for more than an hour and then voltage was still 12.5 (with some help from the panel).
Eventually i switched off before it stopped.
So leasson learned is that probabaly the other appliances play some role (i suspect the car radio) and the charging needs to be more sriously taken, Eventually even if voltage is high maybe the charging is not perfect.
Thanks all for your valuable comments.
So i did today a more seroius test. Battery fully charged (was one month idle with 50W solar panel connected) showed 13.8.
All other pplianced shut off.
So the fridge ran for more than an hour and then voltage was still 12.5 (with some help from the panel).
Eventually i switched off before it stopped.
So leasson learned is that probabaly the other appliances play some role (i suspect the car radio) and the charging needs to be more sriously taken, Eventually even if voltage is high maybe the charging is not perfect.
Thanks all for your valuable comments.
Refueler
Well-known member
Radios ..... many of todays radios even though more solid state than the older .. demand some serious power. We all like a decent sub woofer and speakers ... that adds up very quickly.
Its so bad now - that if I sit in car and listen to music - I have engine running if more than just a few minutes .. I have in past had my car fail to start because of sitting listening to radio ....
Its so bad now - that if I sit in car and listen to music - I have engine running if more than just a few minutes .. I have in past had my car fail to start because of sitting listening to radio ....
vas
Well-known member
I'd still check voltage at battery vs voltage at the fridge controller input terminals while running. If you find there's a decent discrepancy, I'd start investigating all connections and fuse/breakers for losses.
I have the Uni-T linked in post #28 and has helped me in numerous occasions, well worth the investment.
The first one I bought was AC ampclamp only, donated to a friend...
Having said all that, on a 24V@220Ah bank I had before lifepo4, I could get a fridge up and running for a few days wihtout solar. 12V@80Ah is not much if anything else is runing (say VHF, big amp radio, normal lights, etc)
I have the Uni-T linked in post #28 and has helped me in numerous occasions, well worth the investment.
The first one I bought was AC ampclamp only, donated to a friend...
Having said all that, on a 24V@220Ah bank I had before lifepo4, I could get a fridge up and running for a few days wihtout solar. 12V@80Ah is not much if anything else is runing (say VHF, big amp radio, normal lights, etc)
Boater Sam
Well-known member
The wire to the fridge may well be 6mm but how long is the run? Volts drop in the cable is the usual problem with 12v fridges.
Rule of thumb, for every metre of cable between the battery and the fridge you need 1mmSq of copper, So your 6mm will run a fridge on cables 6m long.
Rule of thumb, for every metre of cable between the battery and the fridge you need 1mmSq of copper, So your 6mm will run a fridge on cables 6m long.
vasant
Member
thanks but cables were replaced 3 months ago. Indeed 80Ah is very little but as said fully charged it should provide the needed 3 AMps for some hrs