Voltmeter for vehicle battery to monitor inside of cab

[Sorama]

You claim to be some world class engineer however you lack even basic social skills it is clear.

You can’t be both   
But I’m old enough to know I’m not a world class engineer, on the contrary.
And I do have some decades of automotive experience as a job.

Anyway, good luck trying to find the culprit.
( it’s probably not even car related)

[electroniclearner820327]

A temporary voltmeter hook-up direct to the battery isn't too difficult in most vehicles, and can be done dirt cheap.   Take some low current double-insulated flat twin mains flex, a couple of crimp ring terminals to fit your battery terminals, an inline fuseholder and a pair of 4mm banana plugs, and wire as previously described, leading the wire out from under the hood near the hinge, and in through the passenger door to a cheap DMM (preferably without auto-poweroff) in a cell-phone holder on the dash.   Drill a couple of 4mm holes in a small block of wood or plastic to have something to 'safe' the plugs with if you disconnect the DMM.  Do check where the cable is pinched by the hood and door frequently to make sure it isn't chafing. 

If you want the convenience of a lighter socket voltmeter,  it wont take long to see if it matches the DMM's reading of the voltage at the battery closely enough to be useful.  Note that if a connection goes high resistance, a previously good lighter socket voltmeter may become significantly inaccurate *WITHOUT* *WARNING*, so its best *NOT* used for fault diagnosis but only for monitoring a known working charging system that is slightly inadequate, or monitoring how much 'juice' you've got left when off-grid.  If it gives even slightly unexpected readings, you need to check the actual battery terminal voltage.

One of the things I keep in the electrical toolkit for any vehicle I am responsible for is a spool of hookup wire long enough to reach the length of the vehicle, with a 4mm plug on one end and a large alligator clip on the other.  It is extremely valuable for tracking down mystery voltage drops in the wiring loom as it lets you easily do a binary search - first determining whether the drop is (mostly) in the positive or negative side, then tracing the affected side of the circuit in order of ease of access to localise the fault.

And for the record, last time I had a persistent battery warning light, I traced the problem to a couple of blown diodes in the alternator, and rebuilt it with a new diode plate^* and changed the internal regulator to resolve it, testing the alternator on the bench charging a battery till I was certain it was reliably repaired, so I'm not *just* an armchair theorist!

* The diode plate was reasonably affordable vs individual press-fit diodes, which I didn't have the proper tooling to install + I had peace of mind that the other four diodes that had been significantly stressed were also being replaced.  The regulator was more of a PITA as the original was discontinued and the replacement had a different pinout.

We have yet another one in favour of direct to terminals too. Is this good person an idiot too who doesn't know what they are talking about?

Soon we may even win a majority!

[Sorama]

A temporary voltmeter hook-up direct to the battery isn't too difficult in most vehicles, and can be done dirt cheap.   Take some low current double-insulated flat twin mains flex, a couple of crimp ring terminals to fit your battery terminals, an inline fuseholder and a pair of 4mm banana plugs, and wire as previously described, leading the wire out from under the hood near the hinge, and in through the passenger door to a cheap DMM (preferably without auto-poweroff) in a cell-phone holder on the dash.   Drill a couple of 4mm holes in a small block of wood or plastic to have something to 'safe' the plugs with if you disconnect the DMM.  Do check where the cable is pinched by the hood and door frequently to make sure it isn't chafing. 

If you want the convenience of a lighter socket voltmeter,  it wont take long to see if it matches the DMM's reading of the voltage at the battery closely enough to be useful.  Note that if a connection goes high resistance, a previously good lighter socket voltmeter may become significantly inaccurate *WITHOUT* *WARNING*, so its best *NOT* used for fault diagnosis but only for monitoring a known working charging system that is slightly inadequate, or monitoring how much 'juice' you've got left when off-grid.  If it gives even slightly unexpected readings, you need to check the actual battery terminal voltage.

One of the things I keep in the electrical toolkit for any vehicle I am responsible for is a spool of hookup wire long enough to reach the length of the vehicle, with a 4mm plug on one end and a large alligator clip on the other.  It is extremely valuable for tracking down mystery voltage drops in the wiring loom as it lets you easily do a binary search - first determining whether the drop is (mostly) in the positive or negative side, then tracing the affected side of the circuit in order of ease of access to localise the fault.

And for the record, last time I had a persistent battery warning light, I traced the problem to a couple of blown diodes in the alternator, and rebuilt it with a new diode plate^* and changed the internal regulator to resolve it, testing the alternator on the bench charging a battery till I was certain it was reliably repaired, so I'm not *just* an armchair theorist!

* The diode plate was reasonably affordable vs individual press-fit diodes, which I didn't have the proper tooling to install + I had peace of mind that the other four diodes that had been significantly stressed were also being replaced.  The regulator was more of a PITA as the original was discontinued and the replacement had a different pinout.

We have yet another one in favour of direct to terminals too. Is this good person an idiot too who doesn't know what they are talking about?

Soon we may even win a majority!

On the contrary ; you should read it again and accept there is a relation between the voltage reading and knowing if there is somehow an issue with either battery or the generator.
Those who are into automotives have that experience , that knowledge.

It seems you have forgotten your own question.

[electroniclearner820327]

Anyway, good luck trying to find the culprit.

Thank you for your kind wishes.

[Analog Kid]

Your just pretentious.

You spend most of your time belittling beginners on this subforum. You have a serious inferiority complex. You claim to be some world class engineer however you lack even basic social skills it is clear.

Um, is it possible that you missed something here? They were responding to @radiolistener (who is definitely not a beginner), not you.

I don't think anyone here has belittled you, have they?

BTW, what do you think about my suggestions above?

[electroniclearner820327]

Your just pretentious.

You spend most of your time belittling beginners on this subforum. You have a serious inferiority complex. You claim to be some world class engineer however you lack even basic social skills it is clear.

Um, is it possible that you missed something here? They were responding to @radiolistener (who is definitely not a beginner), not you.

I don't think anyone here has belittled you, have they?

Yes they have been condescending many times towards me in this post and others.

BTW, what do you think about my suggestions above?

Good suggestions, which is why I thanked you on that post. 

EDIT: Btw I give respect to the moderators in their hands off approach on this forum. They dropped in and despite the wild ride of shittalking they only commented gently to lay off the politics.  If it was reddit the whole thing would have been locked at the first 'micro-aggression'.

[BeBuLamar]

yep   always measure at battery terminals

had problems  with bad contacts on relays,  old cars with mechanicals  on /off  lights switches and others,  because you may have carbon deposits, oxydation  and other factors

now you have so many gadgets who do that, even cheap bluetooth ones ...  they consume very little, and if your car runs at least once a week, no major battery drain occurs


a cigarette lighter can be useful,  but not for real troubleshooting and battery drain problems, they can occur elsewhere

Now we are getting some more support for team battery terminals! 

Could it be we aren't just fringe crazies after all like the 'majority' have made us out to be?

I don't even think there is 1% difference between the battery terminal and the cigarette lighter socket. The DMM has input impedance of 10MOhms how much resistance between the battery terminal and the lighter socket it has to be in order to drop 1%?  About 100KOhms.

[radiolistener]

This entire thread has been distorted, demolished and almost totally destroyed by one poster, @radiolistener.

Not at all. What’s really happening here is an attempt by some to promote dodgy technolgy methods or promote cig-lighter gadgets as the best way to check a battery. That would be one thing, but what’s truly surprising is their persistence in rejecting proper testing approaches and insisting on questionable dodgy methods instead.

Initially, there was pressure claiming that this is the crowd opinion, and now the assertion is that Bosch’s official protocol involves checking charging status via a voltmeter at the cigarette lighter. From my opinion not a smart approach 

Maximum of about 1% voltage drop between battery and lighter socket.

The problem is that this “about 1%” applies only to a specific vehicle under specific conditions. In a different vehicle and different conditions, the voltage difference may be significantly different, and there’s no reliable way to predict exactly what it will be in your case and how it will vary over time.

Do what the poster above did. Measure the voltage at both the battery and cig lighter socket.

If the cig-lighter socket reading is close enough to the battery reading for you, go ahead and use the lighter socket for voltage measurement.

That approach can be used, but only with the understanding that the voltage difference you observed earlier can change at any time due to various factors like corrosion, vibration, etc. Therefore, relying on such measurements isn’t advisable - you should always verify directly at the battery terminals using a proper multimeter.

I use voltage readings from security system via a remote control unit in the same this way, periodically cross-checking them against direct measurements at the battery terminals. This allows me to monitor the voltage remotely. And with periodic check at the battery terminals I can see difference and observe its fluctuations of that difference over time. The difference is usually about ±0.1-0.2 V depending on some factors, probably temperature.

But note, while this method allows you to measure battery voltage and estimate its level of charge, it does not verify whether the battery is being properly charged. Generator components often fail - such as the regulator, windings, or belt, resulting in improper charging that can also quickly lead to fail the battery. Although a voltmeter can sometimes help detect this, it’s not straightforward and not easy. The simplest and most reliable method is to use a clamp meter like UT210 to measure the direction and magnitude of the current while the alternator is running, comparing these results with the battery’s charge level and alternator specification.

The most problematic situation is that a faulty alternator can damage a new battery, and conversely, a failing battery can cause alternator failure. Therefore, it’s important to check both components together.

I know of cases among acquaintances where they frequently replaced the battery without realizing the underlying issue was the alternator. There was even an instance where someone replaced the alternator but kept the old battery that had existing problems, which ultimately led to the failure of both the new alternator and the old battery.

Just so you know, there's nothing that mysterious about car electrical wiring: all devices in the car are connected together to the 12-volt source (the battery). No in-line resistors or anything like that to drop the voltage.

I would not agree, this information is not accurate. Automotive wiring is quite complex, even for experienced professional electricians. Every wire has inherent resistance, it’s not a superconductor, so there will always be some voltage drop depending on the current flowing through it. Moreover, modern vehicles have thousands of wires interconnected in complex network, making it quite challenging to trace and analyze voltage drops accurately, even for seasoned specialists.

The situation is further complicated by the fact that automotive wires and contacts are exposed to harsh environmental conditions and strong vibrations, which negatively affect contact reliability and increase resistance, including leakage currents through insulation damaged by vibration.

I am quite confident that even the most skilled wiring technician cannot instantly identify all connection details without consulting the technical documentation specific to that vehicle.

Yes, yes: as @radiolistener has been obsessively pointing out, the best place to measure battery voltage is at the battery. However, that is a problematic way to measure it; as others have pointed out, if your meter draws any significant current and it's permanently connected to the battery, it can drain it over time. (Plus the problem of a much longer connection if you want the meter to be inside the car.)

I disagree that this is problematic. It’s quite simple - just place a DMM in the trunk. You already need to open the hood periodically to check fluid and oil levels, so measuring voltage directly at the battery terminals is no more complicated.

If you have doubts about alternator and charging, get a clamp meter like the UT210, diagnostics will take only a couple of minutes. There’s no need to connect any dodgy technology gadgets that would constantly and unnecessarily drain the battery.

I perform this check regularly and have no need for additional gadgets.

[Analog Kid]

This entire thread has been distorted, demolished and almost totally destroyed by one poster, @radiolistener.

Not at all. What’s really happening here is an attempt by some to promote dodgy technolgy methods or promote cig-lighter gadgets as the best way to check a battery.

No.

That's your misrepresentation of the issue here.

Nobody has said, nor would they say, that using the lighter socket is the best way to check a battery. Nobody.

What we're saying is that in most cases, absent any significant wiring deficiencies, checking the battery voltage at the lighter socket is good enough for most purposes (and evidently for the OP's purposes, which is the important thing here, as we're dealing with their question). As in within 1%.

You're the one with the anal fixation on only ever using a test directly at the battery terminals as acceptable.

It's up to the OP now. If they follow my (and others') suggestions, they'll do some measurements of their own; if they're really curious they can test both at the battery terminals and at the lighter socket. If the latter is within 1% of the former, then Bob's your uncle, as they say.

[Simon]

You made it painfully clear you’re not able to accept others knowledge nor experience. 

You even think you’re smarter than your own dealership.
They surely had a good time when you were trying to counter them.
Have fun explaining TS what and how to proceed.

 

I did not ask for your opinion about my knowledge or your judgment of me. I posed a straightforward question: is it your personal opinion that verifying proper battery charging should be done by measuring voltage at the cigarette lighter instead of using current clamp meter near the battery terminal, or is this an official Bosch company protocol?

I’m starting to get the impression that you’re deliberately misleading people and damaging the company’s reputation by attributing such questionable practices to them. Fortunately, verifying this is simple - we can submit an official inquiry and see how Bosch responds on the matter. Let’s see then who’s actually writing bullshit.

I’m waiting for your confirmation: if you insist that this is truly Bosch’s official protocol, I will submit a formal inquiry to Bosch on this matter and share their response here. 


PS: By the way, it appears that I’ve previously contacted Bosch regarding a battery-related issue, so I already have their official contact information.

Then just contact Bosch instead of using it as a threat that you are right, maybe while you wait for the answer you will stop derailing the thread!

[radiolistener]

No.

That's your misrepresentation of the issue here.

Nobody has said, nor would they say, that using the lighter socket is the best way to check a battery. Nobody.

No, there is no misrepresentation, I'm talking about these claims:

I knew someone would bring this up, but I think it only complicates things. He just needs some idea of if and when the battery is being charged. That's why I suggested the cigarette lighter socket. It will be more than sufficient to do the job.

I have been analyzing car electronics and car battery issues for more than 20 years.
You can reliably measure the battery voltage at any point in the car.

And try to understand why I’m telling its better to measure somewhere down the road instead of next to the battery.
It seems I have to explain some basics too.

Reviewing the discussion from the beginning, I am increasingly convinced that all these claims about measuring through the cigarette lighter are part of a coordinated marketing campaign by trolls, apparently aimed at promoting questionable gadgets designed for the cigarette lighter socket. 

[Analog Kid]

No.

That's your misrepresentation of the issue here.

Nobody has said, nor would they say, that using the lighter socket is the best way to check a battery. Nobody.

No, there is no misrepresentation, I'm talking about these claims:

I knew someone would bring this up, but I think it only complicates things. He just needs some idea of if and when the battery is being charged. That's why I suggested the cigarette lighter socket. It will be more than sufficient to do the job.

"More than sufficient" ≠ "better".

So far as those other two go, they were saying that it's better to measure at the lighter socket not because it's more accurate but because it's more practical to the OP's purpose and would be accurate enough.

You seem to completely lack an understanding of the concept "accurate enough for my purposes".

[radiolistener]

Then just contact Bosch instead of using it as a threat that you are right, maybe while you wait for the answer you will stop derailing the thread!

Yes, I intend to contact Bosch, but first I would appreciate clarification on whether the claim about measuring via the cigarette lighter reflects Sorama’s personal opinion, which may not align with Bosch’s official protocol, or if it is indeed a practice genuinely followed by Bosch engineers. The scope and nature of my inquiry will depend on this distinction.

[langwadt]

the cigarette lighter is is rated for 10-15A, if it doesn't show battery voltage something else is seriously wrong

[radiolistener]

"More than sufficient" ≠ "better".

So far as those other two go, they were saying that it's better to measure at the lighter socket not because it's more accurate but because it's more practical to the OP's purpose and would be accurate enough.

You seem to completely lack an understanding of the concept "accurate enough for my purposes".

The phrase "accurate enough" applies only when the chosen measurement method is technically appropriate for the diagnostic goal. In this case, the TS asked how to verify whether the battery is being charged correctly - not merely whether some voltage is present in the system or whether the alternator activation causes a shift in potential distribution across the vehicle’s wiring.

Voltage measurements alone, particularly at auxiliary points such as the cigarette lighter socket, cannot provide reliable or meaningful information about the charging process. Without direct assessment of the actual charging current flowing into the battery, voltage readings are insufficient and potentially misleading when evaluating charging quality.

Presenting such indirect measurements as "sufficient" risks misinforming users and promoting incorrect diagnostic practices.

[SteveThackery]

Not at all. What’s really happening here is an attempt by some to promote dodgy technolgy methods or promote cig-lighter gadgets as the best way to check a battery.

Hey, wait, wait! Nobody said it was the best way! I, and others, have said it's a perfectly adequate way - and probably the easiest - to check for a correlation between a lower battery voltage and the battery light coming on.

I stand by that.

[SteveThackery]

The phrase "accurate enough" applies only when the chosen measurement method is technically appropriate for the diagnostic goal. In this case, the TS asked how to verify whether the battery is being charged correctly - not merely whether some voltage is present in the system or whether the alternator activation causes a shift in potential distribution across the vehicle’s wiring.

Voltage measurements alone, particularly at auxiliary points such as the cigarette lighter socket, cannot provide reliable or meaningful information about the charging process. Without direct assessment of the actual charging current flowing into the battery, voltage readings are insufficient and potentially misleading when evaluating charging quality.

Presenting such indirect measurements as "sufficient" risks misinforming users and promoting incorrect diagnostic practices.

Good grief! 

[Analog Kid]

The phrase "accurate enough" applies only when the chosen measurement method is technically appropriate for the diagnostic goal. In this case, the TS asked how to verify whether the battery is being charged correctly - not merely whether some voltage is present in the system or whether the alternator activation causes a shift in potential distribution across the vehicle’s wiring.

Voltage measurements alone, particularly at auxiliary points such as the cigarette lighter socket, cannot provide reliable or meaningful information about the charging process. Without direct assessment of the actual charging current flowing into the battery, voltage readings are insufficient and potentially misleading when evaluating charging quality.

Presenting such indirect measurements as "sufficient" risks misinforming users and promoting incorrect diagnostic practices.

Good grief! 

Obviously he'd only be satisfied with a dedicated, permanently-installed voltage monitor (7.5 DMM?) and a shunt in line with the battery to measure current, accurate to 0.01%.

Something the OP never remotely asked for, BTW.

Talk about missing the point ...

[radiolistener]

the cigarette lighter is is rated for 10-15A, if it doesn't show battery voltage something else is seriously wrong

If you're specifically interested in measuring the battery voltage itself, even mentioned 1-2% error means approximately 0.25V at 12.7V, which translates to about a 25% error in estimating the battery level of charge - quite significant. When you know average difference with real  battery voltage you can live with it depending on your "accurate enough" interpretation.

However, this isn’t the main issue here. The TS asked how to verify whether the battery is charging correctly, meaning whether the alternator and its regulator are functioning properly - not how to check the level of charge. And that cannot be determined either through the cigarette lighter socket or even by measuring voltage directly at the battery terminals. Proper charging assessment requires monitoring the actual charging current flowing into the battery. It requires current clamp meter.

[radiolistener]

Obviously he'd only be satisfied with a dedicated, permanently-installed voltage monitor (7.5 DMM?) and a shunt in line with the battery to measure current, accurate to 0.01%.

Something the OP never remotely asked for, BTW.

Talk about missing the point ...

Please don’t project your assumptions onto me. As I’ve explained multiple times, for alternator diagnostics I use a simple UT210 clamp meter, which is more than sufficient and takes just a couple of minutes. It can measure voltage either. For monitoring battery charge level, even a basic DT830 multimeter with 3 digits fully meets my needs.

So kindly stop attributing to me false demands I never made.

PS: That said, I do own a 6.5-digit DMM either and occasionally use it for automotive measurements. In fact, when charging a car battery, I usually monitor the voltage using my 6.5-digit DMM, not for the sake of precision, but simply because it’s positioned right next to the power supply I use for charging. I see nothing wrong with using higher-grade equipment.

[Analog Kid]

Obviously he'd only be satisfied with a dedicated, permanently-installed voltage monitor (7.5 DMM?) and a shunt in line with the battery to measure current, accurate to 0.01%.

Something the OP never remotely asked for, BTW.

Talk about missing the point ...

So kindly stop attributing to me false demands I never made.

It was, it was a, a, it was a joke, son.
Apparently your irony detector is badly in need of recalibration.

[radiolistener]

There’s one important consideration when checking the alternator using the UT210 - starter current exceeds its measurement range, so it’s important to remove the clamp from the cable during engine start to avoid clamp meter damage. But as a plus it works very well for measuring standby current with the engine off and all consumers switched off.

[electroniclearner820327]

I disagree that this is problematic. It’s quite simple - just place a DMM in the trunk. You already need to open the hood periodically to check fluid and oil levels, so measuring voltage directly at the battery terminals is no more complicated.

If this is your main reasoning then you actually have totally missed the point of the OP!

The whole thing is about doing it conveniently in real time. I stated I have already done it several times by popping the hood and now don't want to do that any more and rather have a more convenient way to monitor it on the fly, while driving.

If the cigarette port method will do that, albeit at a little less accuracy, then I am with those guys. It is not about extreme accuracy, just to know that the alternator is working and charging so then I can feel I can not pay attention to the battery light being on when it does decide to illuminate.

[electroniclearner820327]

This entire thread has been distorted, demolished and almost totally destroyed by one poster, @radiolistener.

Not at all. What’s really happening here is an attempt by some to promote dodgy technolgy methods or promote cig-lighter gadgets as the best way to check a battery.

No.

That's your misrepresentation of the issue here.

Nobody has said, nor would they say, that using the lighter socket is the best way to check a battery. Nobody.

What we're saying is that in most cases, absent any significant wiring deficiencies, checking the battery voltage at the lighter socket is good enough for most purposes (and evidently for the OP's purposes, which is the important thing here, as we're dealing with their question). As in within 1%.

You're the one with the anal fixation on only ever using a test directly at the battery terminals as acceptable.

It's up to the OP now. If they follow my (and others') suggestions, they'll do some measurements of their own; if they're really curious they can test both at the battery terminals and at the lighter socket. If the latter is within 1% of the former, then Bob's your uncle, as they say.

As per my post above, I believe I may have broken out of the radiolistener spell now when I read their reply that they had no consideration for convenience in this, which is the whole point of my post!

I think in that case their name might better be radiosilence as they have not listened to anything I was saying in hammering only at the terminals point. 

If the cigarette lighter socket is good enough for the task I actually want it for, which is only to give a gross indication of voltage spiking to indicate that the alternator is charging, then I agree they have wasted everyone's time arguing about something that is absolutely besides the point.

I am not experienced enough to know one way or the other whether their point is salient or not as to whether the cig socket is too inaccurate to be useful but I leave that to you guys to slug it out.

As you mention though, Analog Kid, I can test myself with my DMM. I apologize for ignoring your patient advice but please cut me some slack as I was in a cult and could not see outside of it for that time.

Getting back to actual practical matters which may help my situation then...I have since gone and bought a cheap digital meter which only has the bare wires. As such how could you guys advise I connect it up now, considering it has not cigarette port socket? Buying a socket would probably make it cost as much as a ready made one. If you are all saying that it doesn't matter where on the vehicle electrical system it goes, is there some other place I could wire it up without having to run cables out anywhere and it was mentioned earlier that wiring to my dc-dc charger with 40A would be a no go.

EDIT: Actually probably better to just buy a cigarrette insert as I guess only a couple of pounds and probably easier than rummaging around looking for wires to piggy back to and still cheaper. I have bought the little voltmeter now so might as well make use of that and make my own one for the cig port.

I agree now the thread was hideously derailed by radiolistener. 

Ok I am doing some research and just reading the wiki on the DC power plug the answer was revealed to me right in this sentence!:

The voltage of the power outlet is usually near 12 V DC, and may be elevated between 13.5 V to 15 V while the engine is running. On trucks, the voltage of the power outlet may be near 24 V DC.

https://en.wikipedia.org/wiki/Automobile_auxiliary_power_outlet

[electroniclearner820327]

Can someone explain to me why I can't add another wire on the dc-dc charger line? It was told 'no' without explanation.

Yes there will be 40A amps but can't I somehow make another circuit on that line and limit the amps going through just the side circuit? Is it simple or not to do that? Btw I was told by the charger manufacturer when fault finding that I shouldn't be worried about putting the DMM on the positive and negative while it is running as it won't cause the current to go through it so why would it be different in this case?

As I want to use it for the foreseeable future I don't want the 12v plug always in use so I couldn't plug in other things, preferably. So I would prefer it had its own dedicated circuit.