Hello all, I think That I saw something about a digital volt meter on here some time ago but cannot find it. I am looking for something to tell me what state the battery is in when using solar panels. Up til now I have used a conventional 'avo' meter with the two pin 12 volt plug attached, so that I can plug in to the 12 volt auxilliary socket and thus avoid having to go out and open the battery locker.but it is a bit cumbersome and I see now that there are some available that are Pre set to 12volts DC and can just be plugged into a cigar lighter connector. I think that some will also show amps reading. When I looked on Maplins site, they had one for about £7 but on the picture I think that it had just a single probe coming out of it, and wonder how that works. I should be able to use the meter on Baileys panel but it is so inaccurate ( and hard to see,) that I prefer a digi readout
Digital 12volt meter
- Thread starter RodOne1
- Start date
Damian
Moderator
The only accurate way of seeing what the battery is doing is at the battery terminals.
Anywhere else and you bring in voltage drop through the wiring, additional connections etc.
Using something pre set to 12v is not much use as you will be looking at 13.8 to 14v at the battery.
Anywhere else and you bring in voltage drop through the wiring, additional connections etc.
Using something pre set to 12v is not much use as you will be looking at 13.8 to 14v at the battery.
Hello Damian,
Thanks for your reply. Since posting I found that device on Maplins and decided that it was not what I need . On Amazon though, they had a gadget for £3 that will measure the battery in the range I require. For that price I will give it a go! I hear what you say Re voltage drop, but when I used to use the multimeter it seemed to give me fairly accurate readings, and when I occasionally double checked with the readings across the battery terminals, it was never far off. I expect the battery drop is partly the reason why Baileys own needle display is so far adrift. On the newer vans now, they seem to fit much better displays, showing the battery charge, but as I only now spend around 3 months per year without EHU, it is not really. so much an issue.
Thanks for your reply. Since posting I found that device on Maplins and decided that it was not what I need . On Amazon though, they had a gadget for £3 that will measure the battery in the range I require. For that price I will give it a go! I hear what you say Re voltage drop, but when I used to use the multimeter it seemed to give me fairly accurate readings, and when I occasionally double checked with the readings across the battery terminals, it was never far off. I expect the battery drop is partly the reason why Baileys own needle display is so far adrift. On the newer vans now, they seem to fit much better displays, showing the battery charge, but as I only now spend around 3 months per year without EHU, it is not really. so much an issue.
Damian
Moderator
At work we always found the AVO multi meter far superior to anything else even the digital meters, but that was 20 years ago! Why spend money when you have perfectly good multi meter that will give you the accuracy you need?
There is often a misconception that just because a system is digital it must be right, that can be far from the truth. In reality unless a meter is calibrated and the sytems error is known you cannot trust any meter digital or analog.
However for the purpose of monitoring battery condition, a meter that can resolve to 0.1V should be more than adequate. The AVO analog meters are fine devices, but even these need recalibrating from time to time to be certain of their accuracy.
If the intention is to have a permamant display, then you need to consider how the meters work. Avoid moving iron meters which are relatively inaccurate and the will use a modest current
An analog moving coil meter with a current limiting resister will use a very small current from the potential difference being monitored to activate the needle, But a digital meter may need to have a seperate battery to power the measurment electromics. Some digital automotive meters may use current from the measureand (like the analog meter) to power the display.
For simply monitoring battery voltage, a pair of wires from the battery to anywhere in the caravan that ONLY feed the volt meter should be fine, as there is virtually no current being used so voltage drop will not be a problem.
However for the purpose of monitoring battery condition, a meter that can resolve to 0.1V should be more than adequate. The AVO analog meters are fine devices, but even these need recalibrating from time to time to be certain of their accuracy.
If the intention is to have a permamant display, then you need to consider how the meters work. Avoid moving iron meters which are relatively inaccurate and the will use a modest current
An analog moving coil meter with a current limiting resister will use a very small current from the potential difference being monitored to activate the needle, But a digital meter may need to have a seperate battery to power the measurment electromics. Some digital automotive meters may use current from the measureand (like the analog meter) to power the display.
For simply monitoring battery voltage, a pair of wires from the battery to anywhere in the caravan that ONLY feed the volt meter should be fine, as there is virtually no current being used so voltage drop will not be a problem.
I am obsessive about my battery! We do a lot off mains and until I had a panel I checked my battery twice a day. I use a Maplins digital meter, cost £5 about 8 years ago. The size of a small *** packet with 2 probes. I poke them in the cigarette socket. It might not be calibrated but gives me a reasonable idea. The on board analogue one is useless. The CC handbook has a scale for converting voltage into % charge.
Voltage State of Charge 12.6+ 100% 12.5 90% 12.42 80% 12.32 70% 12.20 60% 12.06 50% 11.9 40% 11.75 30% 11.58 20% 11.31 10% You may find this helpful Steve W
Thanks for that Steve. This is the type of scale that I have always used as a good guide, and I like to know the sort of voltage the solar panels are producing. So far, I have never suffered a flat battery, despite being EHU free for over two months at a time. We do not use a lot of TV, and I use a battery Roberts radio rather than the one that Bailey supplied. We use everything else though, and for many years now I have used led lighting- though it is now pretty much a standard fitment in new vans. i always pick my moments before running the pump for extended times such as filling the onboard tank, which I do in bright sunlight so the solar panels are helping out.Before the days of flat screen telly, some of the older TV sets would give you a warning if your battery was getting low- normally late at night when the other half would run a tap to teeth brush.
I use a digital voltmeter from Conrad Electronics (from the web) Item Ref. 134473 which measures low voltages to 2 decimal places. It is a small oblong panel meter. I cut a small hole in a cupboard bulkhead so its hidden away except when you want to check. You also need a varistor for protection (Item 46750) Total cost £24, they also have an advice line. As the meter draws hardly any current there is virtually no volts drop wherever you put it near the supply.
Am I getting confused or missing something, or am I just being thick?
If I have the solar panel attached to the battery via the charge controller, & I attach a volt meter to the battery terminals, during the day when the panel is charging the battery, is any reading I see on the voltmeter indicating the voltage as supplied by the battery, or the voltage as supplied by the charge controller? How do I see the state of charge of the battery?
Sorry for the daft question,
Jim
If I have the solar panel attached to the battery via the charge controller, & I attach a volt meter to the battery terminals, during the day when the panel is charging the battery, is any reading I see on the voltmeter indicating the voltage as supplied by the battery, or the voltage as supplied by the charge controller? How do I see the state of charge of the battery?
Sorry for the daft question,
Jim
JimD said:
A voltmeter would give the output voltage of the charge controller if panel is connected in daylight. Either wait until it is dark or if you really have to know use a hydrometer as in old school battery testing. TBH it never concerns me too much as the charge level of the battery in going to increase during the day with the use of the pv panel. At the best voltmeters are a crude measurement of charge state.
I was thinking something along the lines of one of these.
http://www.ebay.co.uk/itm/Mini-Yellow-LED-Digital-Voltmeter-Voltage-Volt-Meter-Panel-3-3-30V-/360497700244?pt=UK_BOI_Electrical_Test_Measurement_Equipment_ET&hash=item53ef565d94
Small 3.3 to 30v, wired to the battery terminals, and probably something as easy as velcro to the side of the battery.
Just open the battery compartment door and have a look.
Guess so long as it is reading at least 12.6v things are good ?
Mat
http://www.ebay.co.uk/itm/Mini-Yellow-LED-Digital-Voltmeter-Voltage-Volt-Meter-Panel-3-3-30V-/360497700244?pt=UK_BOI_Electrical_Test_Measurement_Equipment_ET&hash=item53ef565d94
Small 3.3 to 30v, wired to the battery terminals, and probably something as easy as velcro to the side of the battery.
Just open the battery compartment door and have a look.
Guess so long as it is reading at least 12.6v things are good ?
Mat
Have ordered one of the volt meters in my post above.
With such a small current draw is there a need to fuse it ?
Thanks
Mat
With such a small current draw is there a need to fuse it ?
Thanks
Mat
Hello Mat.
I think you may misunderstand the safety aspects of electrics. Just because a device has a low current consumption, you still need to protect the wires in the event of a fault occurring, such as a short circuit.
That's why fuses or over current devises are a very important even on 12v systems.
If someone were to push a drawing pin through the wires and create a short, even a 12v system has enough power to heat up the small wires enough to start a fire, especially where lightweight caravan woods are concerned.
I would suggest a 50 or 100mA fuse in the positive lead as close to the battery as possible.
I think you may misunderstand the safety aspects of electrics. Just because a device has a low current consumption, you still need to protect the wires in the event of a fault occurring, such as a short circuit.
That's why fuses or over current devises are a very important even on 12v systems.
If someone were to push a drawing pin through the wires and create a short, even a 12v system has enough power to heat up the small wires enough to start a fire, especially where lightweight caravan woods are concerned.
I would suggest a 50 or 100mA fuse in the positive lead as close to the battery as possible.
Thanks Prof.JL
I shall fuse it.
My question was really based around the fact that it will be mounted in such away that there can be no accidental damage to the wiring and it would be a circuit of its own, rather than a "load" carrying interactive circuit such as a 12v 5A socket for example, where you are protecting the wiring from damage and over ampage.
Thanks
Mat
I shall fuse it.
My question was really based around the fact that it will be mounted in such away that there can be no accidental damage to the wiring and it would be a circuit of its own, rather than a "load" carrying interactive circuit such as a 12v 5A socket for example, where you are protecting the wiring from damage and over ampage.
Thanks
Mat
Was the Titanic was unsinkable? Your wiring despite your best efforts might still be damaged, if not by you perhaps by someone who has the caravan after you. There is a misconception that when working with 12v systems, because there is virtually no danger of elecric shock from a 12V potential difference that its dosent need to be treated with as much care. Well a 12V lead acid battery can deliver much more current than a 230Vac socket, and given the heating power of such current the danger of fire is probably greater than in the domestic 230V systems.mat said:
Because the meter only requires such a relatively low current, the wires they supply will have a small crossectional area and they require even less of an overload to cause them to self-heat under fault conditions.
I don't wish to be sacre monger so rest assured that a properly installed wiring system should not cause any problems, whetehr its 230Vac or 12V dc. The danger arises when substandard equiepment or wiring is used or if the proper safety precautions are not employed.
As always if you have any doubts, always consult a proffesional electrician.
I measure the current going into the battery using a Maplines current tester that plugs into an inline fuse.The problem with measuring volts is that the difference between fully charged and 1/2 charged is only about 1/2 volt, so you are depending on the acuracy of the meter and to get any accurate result the meter needs to be calibrated - expensive.
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Fitted it today.
Chose to have it on its own fused circuit at the battery terminals.
"Calibrated" it against my digital multimeter and it was reading 0.07v high.
It is very small, just left it sat on top the battery until i get a dry minute to decide where best to stick it.
I bought the yellow coloured version, but think the red would have been a little easier to read in bright sunlight.
Any reading above 12.6v will do me, but with solar panel permenantly fitted it is cycling between 13.1v and 14.5v, so battery is fully charged.
It does what i wanted and that was to give me a quick glance rather than getting the multimeter out and faff about.
Mat
Chose to have it on its own fused circuit at the battery terminals.
"Calibrated" it against my digital multimeter and it was reading 0.07v high.
It is very small, just left it sat on top the battery until i get a dry minute to decide where best to stick it.
I bought the yellow coloured version, but think the red would have been a little easier to read in bright sunlight.
Any reading above 12.6v will do me, but with solar panel permenantly fitted it is cycling between 13.1v and 14.5v, so battery is fully charged.
It does what i wanted and that was to give me a quick glance rather than getting the multimeter out and faff about.
Mat
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