how to use a digital multimeter

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Daydream believer

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I have a pretty standard battery set up on my boat.
2 No. 2 year old 100 amp AGM batteries as domestic. 1 No 35 amp Red Flash battery as a starter. they are connected by a VCR.( forget the make- begings with "V..." & wired as per instruction) The domestics have a single isolator. Te red flash has the same. there is an emergency isolator that would ling all 3 batteries if required.
I have a NASA battery monitor to the domestics only.
I have a Dolphin triple stage charger connected to both domestic & starter batteries. It kicks off at 14.4 volts ( as shown on the NASA) then drops to 13.3 V
The problem is this
I charge the batteries up & they take something like 4.5 amps for some hours. Then this charge drop down to virtually nothing over a 24 hour period. The NASA shows batteries full at 13.3 V.
I turn off shore power & the NASA records a level after a day or two of 12.7 V even though I have the isolators OFF. If I disconnect +ve on all 3 batteries & measure voltage across each one they all read the same. So the starter has charged as it should. Left disconnected they stay at 13V
I suspect that I either have a duff battery drawing the others down, or I have a leak that is running past the isolators- ie can it run back up the battery charger.

So my question is - How do i use the multimeter to check if there is a current discharge on any of the batteries. Where do I put the mutimeter wires & what do I put them to. Do I put them in the circuit or across the circuit somewhere. what do I set the meter to? amps volts ?
I have no idea so guidance would be appreciated please
Thanks
 
Daydream believer said:
I have a pretty standard battery set up on my boat.
2 No. 2 year old 100 amp AGM batteries as domestic. 1 No 35 amp Red Flash battery as a starter. they are connected by a VCR.( forget the make- begings with "V..." & wired as per instruction) The domestics have a single isolator. Te red flash has the same. there is an emergency isolator that would ling all 3 batteries if required.
I have a NASA battery monitor to the domestics only.
I have a Dolphin triple stage charger connected to both domestic & starter batteries. It kicks off at 14.4 volts ( as shown on the NASA) then drops to 13.3 V
The problem is this
I charge the batteries up & they take something like 4.5 amps for some hours. Then this charge drop down to virtually nothing over a 24 hour period. The NASA shows batteries full at 13.3 V.
I turn off shore power & the NASA records a level after a day or two of 12.7 V even though I have the isolators OFF. If I disconnect +ve on all 3 batteries & measure voltage across each one they all read the same. So the starter has charged as it should. Left disconnected they stay at 13V
I suspect that I either have a duff battery drawing the others down, or I have a leak that is running past the isolators- ie can it run back up the battery charger.

So my question is - How do i use the multimeter to check if there is a current discharge on any of the batteries. Where do I put the mutimeter wires & what do I put them to. Do I put them in the circuit or across the circuit somewhere. what do I set the meter to? amps volts ?
I have no idea so guidance would be appreciated please
Thanks
Click to expand...

Meter in series for current, in parallel for voltage. You'd benefit from a bit of private study:

1629658279812.png
 
I think you are measuring the connected batteries with the Nasa monitor and the disconnected batteries with the multimeter. First confirm that both meters read the same by making identical measurements with both meters. They should be the same but at least you can eliminate measurement error. As said above the Nasa monitor is permanently connected and will draw 1.5mA which may be enough to reduce the battery voltage from 13.0V to 12.7V which is still quite a good reading for a resting battery. If you want to measure any leakage current the meter can be connected in series with the negative (or positive) battery connector. Start with a high current setting and reduce it if you don't see a reading. After taking current measurements always put the multimeter leads back in the voltage holes or the next time you go to make a voltage measurement you will blow the internal fuses. (we have all been there)
 
Just to make sure OP understands. Disconnect one battery terminal. Move the positive lead to the meter from "volts ohms" to "current or ma" select amps/milliamps with meter switch to 2000ma (2 amps) Connect one meter lead to battery terminal and one to the wire you have disconnected from the battery. You will probably have no reading ie 0. Move meter switch to 200ma then 20 ma then 2 ma then 200ua. Moving down until you get a useful reading number. That is the current leaving the battery at that time. Do same for other battery. Note you only do this test when you reckon everything is turned off. (as when you leave the boat. ) yes it should show any leakage to battery charger or battery management system. ol'will
 
If you have an Eberspacher or similar type heater thay are often connected direct to the domestic batteries with their own fuse - ie not turned off when isolation switches off. If someone has programmed heat on at set times every day you can easily get flattened batteries if the boat is left for a week or two. Gas detectors also often direct to battery, though a lot less current draw than a heater.
 
jwilson said:
If you have an Eberspacher or similar type heater thay are often connected direct to the domestic batteries with their own fuse - ie not turned off when isolation switches off. If someone has programmed heat on at set times every day you can easily get flattened batteries if the boat is left for a week or two. Gas detectors also often direct to battery, though a lot less current draw than a heater.
Click to expand...
Nothing like that, no independant fridge etc, Only thing permanently connected is the battery charger & the NASA monitor & possibly the alternator, but that should isolate with the positive being shut down.
I just worry that i have 1 duff battery that is pulling the other 2 down or i have something wrong somewhere
 
Daydream believer said:
I have a pretty standard battery set up on my boat.
2 No. 2 year old 100 amp AGM batteries as domestic. 1 No 35 amp Red Flash battery as a starter. they are connected by a VCR.( forget the make- begings with "V..." & wired as per instruction) The domestics have a single isolator. Te red flash has the same. there is an emergency isolator that would ling all 3 batteries if required.
I have a NASA battery monitor to the domestics only.
I have a Dolphin triple stage charger connected to both domestic & starter batteries. It kicks off at 14.4 volts ( as shown on the NASA) then drops to 13.3 V
The problem is this
I charge the batteries up & they take something like 4.5 amps for some hours. Then this charge drop down to virtually nothing over a 24 hour period. The NASA shows batteries full at 13.3 V.
I turn off shore power & the NASA records a level after a day or two of 12.7 V even though I have the isolators OFF. If I disconnect +ve on all 3 batteries & measure voltage across each one they all read the same. So the starter has charged as it should. Left disconnected they stay at 13V
I suspect that I either have a duff battery drawing the others down, or I have a leak that is running past the isolators- ie can it run back up the battery charger.

So my question is - How do i use the multimeter to check if there is a current discharge on any of the batteries. Where do I put the mutimeter wires & what do I put them to. Do I put them in the circuit or across the circuit somewhere. what do I set the meter to? amps volts ?
I have no idea so guidance would be appreciated please
Thanks
Click to expand...

Have you tried checking battery voltage against NASA voltage with mains charger running or engine ? if you have the same voltage difference it's meter error.

Brian
 
William_H said:
Just to make sure OP understands. Disconnect one battery terminal. Move the positive lead to the meter from "volts ohms" to "current or ma" select amps/milliamps with meter switch to 2000ma (2 amps) Connect one meter lead to battery terminal and one to the wire you have disconnected from the battery. You will probably have no reading ie 0. Move meter switch to 200ma then 20 ma then 2 ma then 200ua. Moving down until you get a useful reading number. That is the current leaving the battery at that time. Do same for other battery. Note you only do this test when you reckon everything is turned off. (as when you leave the boat. ) yes it should show any leakage to battery charger or battery management system. ol'will
Click to expand...
Thankyou. That is the sort of guidance I was looking for. I will try later today when on the boat.
halcyon said:
Have you tried checking battery voltage against NASA voltage with mains charger running or engine ? if you have the same voltage difference it's meter error.

Brian
Click to expand...
Readings pretty much the same. A NASA has to be properly set, temp etc to be exact, so can show incorrect charge/discharge figs if very slightly out. That is why I want to use a meter.
 
gordmac said:
Is 12.7v not what a fully charged battery rested for a few days would read?
Click to expand...
Possibly but as soon as plug the charger into shore power it starts punching in amps at a high rate for several hours, as if the batteries are low. The NASA monitor has a battery level indicator that shows that they are only 80% full.
So why are the batteries needing so much of a charge after a few ( 3-4) days when the isolators have been switched to off?
 
The Nasa calculates the remaining capacity from the discharge current and time. If it has lost 20% of 200Ah that is 40 Ah over 80 hrs (3-4 days) or an average of 0.5A. I don't know if it somehow calculates self discharge but if you can't measure any discharge current then perhaps you should check that the Nasa has been set up with the correct battery capacity. The 3 stage charger will first go into bulk charge mode and so would be expected to deliver a reasonable charge until it detects that the batteries are charged and it goes into float mode. This will happen even with fully charged batteries.
 
andsarkit said:
The Nasa calculates the remaining capacity from the discharge current and time. If it has lost 20% of 200Ah that is 40 Ah over 80 hrs (3-4 days) or an average of 0.5A. I don't know if it somehow calculates self discharge but if you can't measure any discharge current then perhaps you should check that the Nasa has been set up with the correct battery capacity. The 3 stage charger will first go into bulk charge mode and so would be expected to deliver a reasonable charge until it detects that the batteries are charged and it goes into float mode. This will happen even with fully charged batteries.
Click to expand...
I agree. The NASA needs to ‘learn’ the batteries and needs to be set up properly in the first place. Try reading the NASA instructions and doing a reset? I fitted a NASA battery monitor to our daughters boat when I did a complete rewire and the zero current reading needed to be adjusted. It’s all in the manual.
IIRC they do two sorts. One monitors one battery and the more advanced one monitors two.
 
john_morris_uk said:
I agree. The NASA needs to ‘learn’ the batteries and needs to be set up properly in the first place. Try reading the NASA instructions and doing a reset? I fitted a NASA battery monitor to our daughters boat when I did a complete rewire and the zero current reading needed to be adjusted. It’s all in the manual.
IIRC they do two sorts. One monitors one battery and the more advanced one monitors two.
Click to expand...
I have done that & had the unit for 16 years so I feel confident it has been set up Ok. It is the single version that monitors the domestic bank, not the starter as well
 
Can't see anything wrong. 12.7V/12.8V is a normal rested voltage, no problem there.

Most chargers, when first turned on will run on bulk/Absorption for a while, even if the batteries are more or less charged.
 
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