Voltmeter for vehicle battery to monitor inside of cab

[electroniclearner820327]

Keep in mind that alternator can't or shouldn't cook the battery, for that you need an external charger.
So initial battery voltage can be higher than what it is after regular use of long enough.

No idea what you mean here but I know that the setup is correct according to the dc charger install specifications.

Alternators do fail. It was old. The mechanic who looked at it said they can fail any time. Adding the charger would have put a massive load on an older alternator so makes sense why it would cause it to fail.

[electroniclearner820327]

   Voltmeter is fine idea.   I paid attention when you mentioned a DC to DC converter,  as that presents a load to the 12V system.  Maybe your trouble light indicates that the inverter load is too high ?  Or other speculation maybe related, to having that inverter (??).

Thanks, it is a logical assertion going only from what I wrote however I was using it for a few months already without this issue arising. The light only started coming on consistently recently out of nowhere, which is why it has me stumped. If it happened soon after having installed a new part it would be easier to diagnose that as the likely culprit but it apparently comes out of the blue which is why I have had a hard time finding the root cause.

So a meter is a good idea but I would just do the cigarette lighter and a DMM. It's not worth to wire and mount a panel meter in the van for troubleshooting purpose. Once you have the problem fixed you don't want the meter there do you?

Yes I will always want it or I would have gotten the lighter port one instead.

It was discussed by some other users here they used to be mounted as standard on vehicles on the dashboard until they went out of fashion.

It is always useful to know and see that the voltage goes up when the engine starts. Do you not want a rev counter or speedometer just because there is no malfunction?

[BeBuLamar]

The problem with a panel meter that most of them today are digital and you need power for them to work. So you need the ingition switch to both turn off the power to the meter as well as the power it measures otherwise you may drain your battery.

[electroniclearner820327]

The problem with a panel meter that most of them today are digital and you need power for them to work. So you need the ingition switch to both turn off the power to the meter as well as the power it measures otherwise you may drain your battery.

Ye I get that but I have some spare switches I will just use one of those but someone else also mentioned that elsewhere and it reminded me I had been thinking about adding a starter battery disconnect anyway at some point because as I live in my van the parasitic drain of opening and closing and central locking and whatever else wastes the battery too.

Been looking up disconnects and saw there are even remote control ones which look appealing so then I won't have to open the hood every single time. One big drawback I saw mentioned in reviews was that you could actually trigger it while driving which could cause serious damage to components. If it was on your keyring in your pocket I could see that happening very easily! However would not be too hard to avoid just putting it somewhere like in one of the shelves around the driver's area and could also take the battery out as still easier than going in to the hood each time.

I only drive once a week average and I have checked the battery before setting off before and looking at my notes it uses about 40-50% through the week while stationary. Haven't had any issue starting it so far but seems a horrible waste of battery charge on useless power draining components.

Do you techies have any better ideas to failsafe the remote disconnect beyond what I have suggested above?

It isn't such a big deal to open the hood each time once per week with a manual one when I park. Less to go wrong in this case.

[BeBuLamar]

I wouldn't go for remote disconnect because the remote control circuit need constant power to work so another thing to drain your valuable power. Do everything manually. You have to run long wires but you can have the switch inside the van. However, if I were you and I only use the van once a week I would leave the large disconnect in the engine compartment and manual switch it on when I want to use the van. Once a week isn't all that much work.

[electroniclearner820327]

I wouldn't go for remote disconnect because the remote control circuit need constant power to work so another thing to drain your valuable power. Do everything manually. You have to run long wires but you can have the switch inside the van. However, if I were you and I only use the van once a week I would leave the large disconnect in the engine compartment and manual switch it on when I want to use the van. Once a week isn't all that much work.

It very difficult to lift the lid brother. I need to lay down after.

Btw I was just looking up low voltage disconnects for my leisure battery when I saw some lower price ones built on arduino or whatever smp thing and it looks like those could be used to disconnect the voltmeter once the engine stops. No way I am tapping the ignition line just for this and would be another cheap option if I am understanding those devices correctly. Looking at the reviews indeed it does look like people are using it for similar purposes:

https://www.amazon.co.uk/Battery-Voltage-Disconnect-XH-M609-Protection/dp/B08BCMH1FY

I could set it to shutoff below 13v as that would be when the alternator was off, and of course when the engine is off too.

[m k]

Keep in mind that alternator can't or shouldn't cook the battery, for that you need an external charger.
So initial battery voltage can be higher than what it is after regular use of long enough.

No idea what you mean here but I know that the setup is correct according to the dc charger install specifications.

Alternators do fail. It was old. The mechanic who looked at it said they can fail any time. Adding the charger would have put a massive load on an older alternator so makes sense why it would cause it to fail.

It means that battery voltage is not very stable definition.
Like a rest voltage and charge voltage where before charging the voltage is lower, but higher voltage is still not charging.

Cooking means that old lead acid battery was fully loaded after few days of caps open, over a boiling point charge voltage and water added when needed.

Your intermittent problem can be anything along the route of electricity.
It also has a general and special problem situations.

General situation is that you have a situation.
Special situation is that you try to pinpoint it.

Old cars have old fixes.
One of mine was a wire between intake manifold and engine block.
The wire had a voltage, but other way was completely unknown and one spot of plastic was melted away.
That exposed spot was also intermittently shorting to block and killing something vital.
Repair was a new insulation from a cut open wire guide tube.

Pinpointing the problem can be very difficult.

If it is intermittently disconnecting spot you can possibly fix it by adding a ring source.
Means that you add a wire from the beginning to the end.
But finally, if not a wire itself, all connections are away from that ring, somewhere is a T-junction.

If it is an overloading spot you need means to record that short moment of the happening.
You also need at least one control spot where the overloading happens a bit later or not at all.

Third possibility is that you swap parts and finally have a gained trust that the problem is gone.

[MrAl]

I wouldn't go for remote disconnect because the remote control circuit need constant power to work so another thing to drain your valuable power. Do everything manually. You have to run long wires but you can have the switch inside the van. However, if I were you and I only use the van once a week I would leave the large disconnect in the engine compartment and manual switch it on when I want to use the van. Once a week isn't all that much work.

It very difficult to lift the lid brother. I need to lay down after.

Btw I was just looking up low voltage disconnects for my leisure battery when I saw some lower price ones built on arduino or whatever smp thing and it looks like those could be used to disconnect the voltmeter once the engine stops. No way I am tapping the ignition line just for this and would be another cheap option if I am understanding those devices correctly. Looking at the reviews indeed it does look like people are using it for similar purposes:

https://www.amazon.co.uk/Battery-Voltage-Disconnect-XH-M609-Protection/dp/B08BCMH1FY

I could set it to shutoff below 13v as that would be when the alternator was off, and of course when the engine is off too.

The best setup I did was some years back when I owned a Volvo.  It had a problem with charging the battery with low automobile use.
I used a 18 gauge wire pair from the battery to the inside cabin compartment, with fuse right at the positive battery terminal.  I ran it though the firewall which was no easy task on that vehicle.  I used a terminal block so I could use the battery for power as well as charging with a solar panel system.
It was easy to measure the voltage that way inside the car, and I designed a system to measure the voltage once every 10 minutes and transmit that reading to a receiver in the house.  The computer (Windows) monitored the receiver and kept a log of all the voltage readings.  Over time I got a good idea what the battery and charging system was doing as well as not doing.  That led to the solar panel system which took care of all that.  Then I could leave the car sit for weeks and not worry about the battery running down.
It was pretty cool getting voltage readings 24 hour a day 7 days a week.  That gives you a lot of history data to work with.
The measurement system has to draw very little current from the battery however so it does not contribute much to the battery drain, unless of course you pair that with a solar charger system.

When I worked in the industry I worked in the power control field, so none of this was really that new to me.  I do realize that there are nuances to some of this that require close attention and careful and concise explanations.  First and foremost, we have to be able to understand each other as well as possible or else it leads to a lot of misunderstandings and back and forth text posts which can take days in forums like this.  Patience is mandatory.

[paulca]

As an alternative to this, to give the OP ideas maybe.

As soon as the engine starts all you will see on the voltmeter is the output voltage of your alternator/regulator.  Around 14.40V.

If your battery is 25 years old and only has 2% capacity remaining, it will still show as 14.40V

The project I have never started was to place a small very low powered circuit that monitors the battery for "dips" in voltage.  Like when you start the car.

So when you start the car the MCU is woken and begins datalogging the voltage into RAM.  When the voltage returns high or goes up to 14.40V the MCU then provides the "Min Battery Voltage" to a BT app.

There are a lot of "ifs and buts" and unsolved questions, but the idea was that everytime you start the car it records the minimum battery voltage.  You don't need to look if you don't want, if the minimum crank voltage drops below a level like 9V it will notify you that your battery may be weak and consider a replacement before winter.

It is in fairness a long way to just "listen", the count of cranks, the pitch of the motor, the "readiness" and "eagerness" to start from a fresh battery is very obvious.  The downside is, the only time you notice is when you put a new battery in.

[electroniclearner820327]

As an alternative to this, to give the OP ideas maybe.

As soon as the engine starts all you will see on the voltmeter is the output voltage of your alternator/regulator.  Around 14.40V.

If your battery is 25 years old and only has 2% capacity remaining, it will still show as 14.40V

The project I have never started was to place a small very low powered circuit that monitors the battery for "dips" in voltage.  Like when you start the car.

So when you start the car the MCU is woken and begins datalogging the voltage into RAM.  When the voltage returns high or goes up to 14.40V the MCU then provides the "Min Battery Voltage" to a BT app.

There are a lot of "ifs and buts" and unsolved questions, but the idea was that everytime you start the car it records the minimum battery voltage.  You don't need to look if you don't want, if the minimum crank voltage drops below a level like 9V it will notify you that your battery may be weak and consider a replacement before winter.

It is in fairness a long way to just "listen", the count of cranks, the pitch of the motor, the "readiness" and "eagerness" to start from a fresh battery is very obvious.  The downside is, the only time you notice is when you put a new battery in.

Didn't really understand that but the  battery is new anyway. Within a year old.

The battery was another thing that died when I added the dc-dc charger. I know you guys will say it was my bad setup but I already knew the battery was weak and in need of replacement because it would struggle to start after being left parked for just a week. It finally totally conked out about the same time as the alternator and would no longer accept charge.

The new one is working nicely. No problems starting through winter. The old one would hardly be able to crank. Just a few chugs and give up if not careful about leaving it for too long but the new one on some cold days I recall it would crank happily for near to 5+ seconds before starting up the engine.

[CatalinaWOW]

Just to re-iterate what I think is a simple solution for OP.

1.  Get a USB tap with voltage monitor.

 A link for typical is

https://www.googleadservices.com/pagead/aclk?sa=L&ai=DChsSEwjJ2tLVw86OAxVpF60GHXRhG7UYACICCAEQAxoCcHY&co=1&ase=2&gclid=Cj0KCQjwyvfDBhDYARIsAItzbZGnEwWlFaOZgD_IAeX9i02FM680rVsNUG4lWBIjSC3RaIvEwHPga0EaAr10EALw_wcB&ohost=www.google.com&cid=CAESeOD29Mc41Jep0n25TZGwVUMSIBd83TF5sbWHETNnSuoJQiIvGrkgjDW9TJ7QT3C8MkBdrWhXrCHA_2c6qfd-vqOFGS4MJZFA5p4yQQUjQ5bwy-HRxXocbn1PmdOlXafuI1l7uWB9UYjduGzcLF-x0K-sP9H6cgSVlw&category=acrcp_v1_41&sig=AOD64_1jL2_TYzHZUFopoh9p4GFRzD2gMw&ctype=5&q=&nis=4&ved=2ahUKEwj5iM7Vw86OAxVzBjQIHXF0HSgQ9aACKAB6BAgFEBw&adurl=


This one has a power switch incorporated so you can assure yourself that the parasitic load is not a problem.

2.  Mount same.  Lots of options here, all dependent on the specific vehicle.   Some have plugs in the dash for installing options on high end vehicles that aren't in yours.  Some have blank dash space or space on the console.  A step drill is your friend here.  If nothing of that type presents buy or fabricate an L bracket which can screw to the bottom of the dash or other appropriate location.

3.  Get a schematic for your vehicle.  It will show which circuits are switched and unswitched by the ignition.  I personally would go for a switched circuit to so as to have no worries about parasitic loads, but it is your vehicle and your choice.   With this information you can easily access the appropriate circuit at the fuse block with the fuse taps mentioned before.  If you actually use the USB charging port you will need to think about a circuit that is designed for enough current that this added load won't be an issue, but on most cars virtually all will be suitable.  Just don't use one that has a 3 amp or possibly a 5 amp fuse.  Note that if you can't find a schematic you can make a good choice based on the names and purposes of the fuses in the fuse block.

4.  Start monitoring.  The voltmeter in these taps is not laboratory grade, not calibrated, only one decimal point resolution, but in my experience they are fairly accurate and you are much more interested in changes than in the absolute voltage.

Anyway, good luck to you with your project.