Poida
11-23-2006, 08:42 AM
What is the prefered instrument to install, a ammeter or a voltmeter and why?
View Full Version : Ammeter V Voltmeter
Swimpy
11-23-2006, 04:45 PM
In my opinion it's the ammeter. It shows how hard your alternator is charging, and will instantly show an alternator, voltage reg., or belt failure. You can estimate how much charge is in battery by how many amps the system is charging.
A voltmeter only shows how many volts in the battery.
Terry
A voltmeter only shows how many volts in the battery.
Terry
Verytricky
11-23-2006, 07:25 PM
hmmmmn.
I always assume my equipment works, so a volt meter whould show my 'energy reserve' and indicate any problems by dropping. When the engine is running 9v = alternator not working, 14 volts says it is.
When at engine off, it allows me to see electrical drain.
I always assume my equipment works, so a volt meter whould show my 'energy reserve' and indicate any problems by dropping. When the engine is running 9v = alternator not working, 14 volts says it is.
When at engine off, it allows me to see electrical drain.
PAR
11-23-2006, 09:38 PM
I also prefer the volt meter, but will mount an amp meter and oil pressure, plus an ignition on light (usually tied to an hour meter) on the engine itself, so I don't have to keep looking back at the instrument panel, while working on an engine.
Frosty
11-23-2006, 10:11 PM
It depends what you want to know. If you want to know if your charging , a light will tell you that. If you need to know how much you need an ammeter. If you need to know if the battery is charged then only a voltmeter will do that one . A digital voltmeter is far better to the point of a analouge voltmeter bieng pretty usless for judging 1/2 a volt which is all the difference between flat and charged.
If your starting from afresh, I would go digital volmeter and one of those battery management sytems that will tell you whats going in whats coming out and how much you have left.
On the other hand most intrumentation like depth sounders etc will give you a digital voltage-- if taken from a sound supply.
If your starting from afresh, I would go digital volmeter and one of those battery management sytems that will tell you whats going in whats coming out and how much you have left.
On the other hand most intrumentation like depth sounders etc will give you a digital voltage-- if taken from a sound supply.
Poida
11-24-2006, 08:57 AM
It would seem from my investigations and from the comments here that an ammeter is the way to go. A voltmeter does not tell you the condition of the battery. For example is one cell is working it will show 12 volts even if there is not enough current to start the engine.
This probably solves the problem I have with one battery, it shows the battery fully charged ie, 12 volts but won't start the engine.
If I install an ammeter it will show the available current.
Thanks for your help.
This probably solves the problem I have with one battery, it shows the battery fully charged ie, 12 volts but won't start the engine.
If I install an ammeter it will show the available current.
Thanks for your help.
Verytricky
11-24-2006, 01:04 PM
If I install an ammeter it will show the available current.
Ummmn - no.
Ummmn - no.
longliner45
11-24-2006, 01:52 PM
ampmeter will be valuable ,,, it will tell you how many amps stored you have left in your battery banks,,for instance if you have 250 amp batterys,,and your running all bildge pumps and (bailing with 5 gallon buckets) and your down to 50 amps ,,,,,make sure you make radio contact with someone ,,longliner,,,,,been there done that.
marshmat
11-24-2006, 04:10 PM
I would install both.
An ammeter tells you how much current is flowing in or out of the battery at that point in time.
A voltmeter tells you the voltage of the battery (duh). Depending what it's hooked to, it can tell you whether your alternator's working, whether the battery's running flat, etc.
Ideally a dedicated battery controller is the instrument of choice, being able to monitor all important parameters- including in some cases an estimate of the energy left in the battery, which neither an ammeter nor a voltmeter alone will tell you.
An ammeter tells you how much current is flowing in or out of the battery at that point in time.
A voltmeter tells you the voltage of the battery (duh). Depending what it's hooked to, it can tell you whether your alternator's working, whether the battery's running flat, etc.
Ideally a dedicated battery controller is the instrument of choice, being able to monitor all important parameters- including in some cases an estimate of the energy left in the battery, which neither an ammeter nor a voltmeter alone will tell you.
Crag Cay
11-24-2006, 04:54 PM
If you need to know if the battery is charged then only a voltmeter will do that one . A digital voltmeter is far better to the point of a analouge voltmeter bieng pretty usless for judging 1/2 a volt which is all the difference between flat and charged.
This is so true. A digital voltmeter is essential, especially for liveabords who need to know the state of their batteries. 12.6V is fully charged, 12.2V is 50 percent discharged and the effective lower limit for a lead acid battery.
A hand held one will even tell you which cell is not working ina battery.
This is so true. A digital voltmeter is essential, especially for liveabords who need to know the state of their batteries. 12.6V is fully charged, 12.2V is 50 percent discharged and the effective lower limit for a lead acid battery.
A hand held one will even tell you which cell is not working ina battery.
luckettg
12-06-2006, 05:18 PM
ampmeter will be valuable ,,, it will tell you how many amps stored you have left in your battery banks,,for instance if you have 250 amp batterys,,and your running all bildge pumps and (bailing with 5 gallon buckets) and your down to 50 amps ,,,,,make sure you make radio contact with someone ,,longliner,,,,,been there done that.
I do not believe the ammeter will show you how many amps are stored in the batteries, but will only show what current is flowing through the circuit it is in. Voltage along with amperage does a better job of showing capacity, and I suggest using a watt meter for a better idea of power flow. This will give a better indication of system capacity and status.
Greg Luckett
I do not believe the ammeter will show you how many amps are stored in the batteries, but will only show what current is flowing through the circuit it is in. Voltage along with amperage does a better job of showing capacity, and I suggest using a watt meter for a better idea of power flow. This will give a better indication of system capacity and status.
Greg Luckett
longliner45
12-06-2006, 07:07 PM
ok what gauge shows stored amps?
stevel
12-06-2006, 07:26 PM
To judge the stored energy in the battery, the "gauge" would need to know the present voltage of the battery, the type of battery, the total storage capacity of the battery, and the "health" of the battery. Only something computerized could do that.
marshmat
12-06-2006, 07:38 PM
Amps (short for amperes) are units of electric current- coulombs per second, to be precise. That's a measure of how much current is flowing through something, in our case the cable to the battery.
Volts are units of electric potential- the driving force that makes current flow. Think of this as the height of the water in a reservoir; more voltage is analogous to more water pressure.
Power is the amount of energy transferred per unit time. Units are watts (one watt = one joule of energy per second). Knowing voltage across a device, and current through it, P=I*V
No gauge can directly measure the amount of energy stored in a battery. With lead-acid cells, a hygrometer can tell you the condition of the battery, ie. what percentage of maximum capacity it's currently at. A sensitive voltmeter that is designed for measuring battery capacity can also provide an estimate of % capacity, if the battery's discharge curve is known (this is what many commercial battery monitor systems do). Or, if you're familiar with basic calculus, you can record current and voltage at regular time intervals, and integrate I*V dT (with respect to time) over the entire time interval since the battery was fully charged; the result is the energy you have drawn out of the battery in that time. Subtract this from the useable energy capacity of the battery to get the energy available. Or if you know the "amp-hour" rating of the battery, integrate I dT to get the amp-hours used. (amp-hours * battery voltage = energy capacity).
The calculations are easy to implement in any spreadsheet if you remember grade 12 math. But don't expect any one gauge to give you the answer on its own. If you want one gauge to say "I have X amount of energy left", you need a battery monitor system designed for the type of battery bank you use.
Volts are units of electric potential- the driving force that makes current flow. Think of this as the height of the water in a reservoir; more voltage is analogous to more water pressure.
Power is the amount of energy transferred per unit time. Units are watts (one watt = one joule of energy per second). Knowing voltage across a device, and current through it, P=I*V
No gauge can directly measure the amount of energy stored in a battery. With lead-acid cells, a hygrometer can tell you the condition of the battery, ie. what percentage of maximum capacity it's currently at. A sensitive voltmeter that is designed for measuring battery capacity can also provide an estimate of % capacity, if the battery's discharge curve is known (this is what many commercial battery monitor systems do). Or, if you're familiar with basic calculus, you can record current and voltage at regular time intervals, and integrate I*V dT (with respect to time) over the entire time interval since the battery was fully charged; the result is the energy you have drawn out of the battery in that time. Subtract this from the useable energy capacity of the battery to get the energy available. Or if you know the "amp-hour" rating of the battery, integrate I dT to get the amp-hours used. (amp-hours * battery voltage = energy capacity).
The calculations are easy to implement in any spreadsheet if you remember grade 12 math. But don't expect any one gauge to give you the answer on its own. If you want one gauge to say "I have X amount of energy left", you need a battery monitor system designed for the type of battery bank you use.
luckettg
12-06-2006, 07:51 PM
That would work ok for a battery system that is not being recharged. Where is the math for the recharging?:)
Simply knowing what the capacity rating of the battery system is supposed to be, then subtracting the power used (Watts), and adding back in the charging capacity will give an approximate idea of the power stored...in a very crude way. For instance, batteries not being charged will draw down in a non-linear way, so the battery power curves would be needed to approximate the stored charge. Voltage is a good indicator of battery condition while the battery is either not being used or is being used, while amps being drawn will also show when capacity is dropping only while the battery is being drawn on. Toss in a charging system and all the voltage or amperage will tell is the the effect of the charging system, not the battery. I have had batteries with open cells on a running engine with the volt and ammeter showing good, until the engine was turned off. Restarting required a jump, then the engine system was up and running again, all lights working, and not any indication of battery problems.
Putting this another way using just a battery and no charging system in the circuit. The loads (lights, radios, etc.) will control the current flow being drawn off the battery. As the battery capacity drops, so will its voltage. This is why voltage is a good indicator of battery condition, and amps are not. Amps will stay constant until the battery voltage drops enough to allow the ammeter to indicate the loss of current due to reduced voltage at the battery.
Greg Luckett
Simply knowing what the capacity rating of the battery system is supposed to be, then subtracting the power used (Watts), and adding back in the charging capacity will give an approximate idea of the power stored...in a very crude way. For instance, batteries not being charged will draw down in a non-linear way, so the battery power curves would be needed to approximate the stored charge. Voltage is a good indicator of battery condition while the battery is either not being used or is being used, while amps being drawn will also show when capacity is dropping only while the battery is being drawn on. Toss in a charging system and all the voltage or amperage will tell is the the effect of the charging system, not the battery. I have had batteries with open cells on a running engine with the volt and ammeter showing good, until the engine was turned off. Restarting required a jump, then the engine system was up and running again, all lights working, and not any indication of battery problems.
Putting this another way using just a battery and no charging system in the circuit. The loads (lights, radios, etc.) will control the current flow being drawn off the battery. As the battery capacity drops, so will its voltage. This is why voltage is a good indicator of battery condition, and amps are not. Amps will stay constant until the battery voltage drops enough to allow the ammeter to indicate the loss of current due to reduced voltage at the battery.
Greg Luckett
marshmat
12-06-2006, 09:36 PM
For recharging, same integral... cumbersome and not ideal for the everyday boater, but this is how we calibrate those power curves in the first place for the lithium polymer packs.
Current is not an indicator of battery condition, not until you start to draw so much that you completely drain it. To use voltage as an indicator of charge level, you need (as Greg describes) the power curves for your pack. And you need a meter that is calibrated accordingly- a standard voltmeter won't do the job, the difference in voltage between full and dead is very, very small.
Current is not an indicator of battery condition, not until you start to draw so much that you completely drain it. To use voltage as an indicator of charge level, you need (as Greg describes) the power curves for your pack. And you need a meter that is calibrated accordingly- a standard voltmeter won't do the job, the difference in voltage between full and dead is very, very small.
longliner45
12-06-2006, 09:42 PM
the reason I asked ,is because on night I was sinking ,,I looked at my amp gauge and it droped to 50 amps,,I knew I was running all pumps ,,before this it read 200,,,,I watched as it draind down to 50,,so I always thought that it measured stored amps....longliner
luckettg
12-06-2006, 09:47 PM
Matt,
How similar are the lithium polymer packs to lead/acid batteries? I usually see a couple of volts difference from charged to discharged in the low dwell batteries I use on sail boats. I usually put a known load on a battery and watch the current flow and voltage for indications as to its condition, and when in doubt, I haul them over to the local supply house to be tested on a battery tester. Oh, the other indicator before that is the way a charger acts when hooked to the battery and how long it takes the battery to recharge (if ever).
Greg Luckett
How similar are the lithium polymer packs to lead/acid batteries? I usually see a couple of volts difference from charged to discharged in the low dwell batteries I use on sail boats. I usually put a known load on a battery and watch the current flow and voltage for indications as to its condition, and when in doubt, I haul them over to the local supply house to be tested on a battery tester. Oh, the other indicator before that is the way a charger acts when hooked to the battery and how long it takes the battery to recharge (if ever).
Greg Luckett
Ike
12-07-2006, 12:51 AM
Voltage tells you the condition of the battery, whether it is fully charged or not and can tell you the condition of individual cells if you have the right monitoring equipment. A hygrometer will tell you this too but only on a wet battery. That won't work on a sealed battery.
An amp meter tells you how much draw there is on the battery, in other words what load you are putting on the battery. This tells you at what RATE the battery is being discharged.
In reverse, when charging a battery an amp meter will tell you the RATE at which a battery is being recharged, but not the state of the battery. A voltmeter tells you that.
Frankly I would have both, come to think of it , I do have both!
An amp meter tells you how much draw there is on the battery, in other words what load you are putting on the battery. This tells you at what RATE the battery is being discharged.
In reverse, when charging a battery an amp meter will tell you the RATE at which a battery is being recharged, but not the state of the battery. A voltmeter tells you that.
Frankly I would have both, come to think of it , I do have both!
marshmat
12-07-2006, 11:52 AM
Greg,
The test you describe in post #18 is pretty much the same as what we do to test the LiPo cells, except we'll run the voltmeter and ammeter to a computer and plot the discharge curve as we do it. Then, battery voltage (ideally between 3.6 V to 4 V) can be used (via that curve) to find the energy left. Similar to what a commerical meter for your lead-acids would do. But in general, integrating the energy flow has proven easier and more reliable when on the run.
I would advise everyone to not try to home-build lithium based batteries unless you know what you are doing. These are an order of magnitude more powerful than lead-acids, but require careful monitoring. If you drop the voltage too low, metallic lithium crystals grow across the electrodes and permanently short-circuit the pack. Cross the terminals, and instead of a spark you get a 3,000 degree arc of nitrogen-oxygen plasma. Leave them crossed and the cell will either vent hydrofluoric acid gas (if you're lucky) or explode (if you're not lucky). When you see these in commercial devices like cellphones, they have sophisticated fail-safe control circuitry attached to keep them happy. Not for the amateur.
The test you describe in post #18 is pretty much the same as what we do to test the LiPo cells, except we'll run the voltmeter and ammeter to a computer and plot the discharge curve as we do it. Then, battery voltage (ideally between 3.6 V to 4 V) can be used (via that curve) to find the energy left. Similar to what a commerical meter for your lead-acids would do. But in general, integrating the energy flow has proven easier and more reliable when on the run.
I would advise everyone to not try to home-build lithium based batteries unless you know what you are doing. These are an order of magnitude more powerful than lead-acids, but require careful monitoring. If you drop the voltage too low, metallic lithium crystals grow across the electrodes and permanently short-circuit the pack. Cross the terminals, and instead of a spark you get a 3,000 degree arc of nitrogen-oxygen plasma. Leave them crossed and the cell will either vent hydrofluoric acid gas (if you're lucky) or explode (if you're not lucky). When you see these in commercial devices like cellphones, they have sophisticated fail-safe control circuitry attached to keep them happy. Not for the amateur.
StianM
12-08-2006, 12:00 AM
Set up a voltmeter with voltemter switch witch allow you to mashure betwen L1-L2, L1-L3, L2-L3, L1-Earth, L2-Earth and L3-Earth.
It will make you able to mashure diference betwen pase-pase and if your voltage betwen pase-earth is less than pase/root off 3 then it's a indication on isolation faliure on that phase.
I would say they are equaly inportant, but if I had to chose I would take the voltmenter.
It will make you able to mashure diference betwen pase-pase and if your voltage betwen pase-earth is less than pase/root off 3 then it's a indication on isolation faliure on that phase.
I would say they are equaly inportant, but if I had to chose I would take the voltmenter.
hartley
12-08-2006, 02:32 AM
For Heavens sake .refer to post number 4 and fit both,plus a few lights and anything else that takes your fancy,itwill only cost a few dollars ,and i am quite sure you will be able to figure it all out !!!!Yea verily i say unto you !!!
Ok i've had a few sherbets pls forgive ......cheers now
Ok i've had a few sherbets pls forgive ......cheers now
marshmat
12-08-2006, 09:50 AM
Right on Hartley, I wouldn't even think about installing batteries without both types of meters....
Stian, we're talking here about batteries- that's DC. Not three-phase AC as you seem to suggest in post #21. I can think of absolutely no reason to have 3-phase on a pleasure craft unless you have diesel-electric power and a really, really large hotel load.
Stian, we're talking here about batteries- that's DC. Not three-phase AC as you seem to suggest in post #21. I can think of absolutely no reason to have 3-phase on a pleasure craft unless you have diesel-electric power and a really, really large hotel load.
StianM
12-11-2006, 11:43 PM
It don't make voltmeter less important if it's a dc system.
A voltage drop that inticate insulation faliure s more critical on a dc system, low voltage dc is even worse to eat up metal on your hull then AC.
I would sugest to also find a isolation guard for it.
On exspresion is that it's posible to save utill you become poor.
Spend money and save money by avoiding truble in the future.
A voltage drop that inticate insulation faliure s more critical on a dc system, low voltage dc is even worse to eat up metal on your hull then AC.
I would sugest to also find a isolation guard for it.
On exspresion is that it's posible to save utill you become poor.
Spend money and save money by avoiding truble in the future.
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