volts vs. amps.

[mellowyellow]

I am familiar with volt gauges and their function<br />to keep track of your battery charging system,<br />but I seem to remember Amp. gauges as a kid on<br />bigger boats. can someone give the uses of each?<br />is there any good reason to have both?<br />just curious...<br />M.Y.

 

[speed29668]

Re: volts vs. amps.

A volt meter measures the voltage the battery is constantly supplying. This gives the general condition of the battery. Anything less than 11 volts should be looked into. Remember, for our purposes consider voltage as always constant. Current, or amps, is a variable quantity. You can think of it as the amount of electricity a circuit or device requires. The more accessories that are in use, the more current required to run these. The fewer items, the less current required. But remember, voltage should always stay constant. An amp meter can be used to determine whether accessories are drawing as much or more current than the alternator can produce, which would not leave much current left over to charge the battery. This is helpful when using outboards with low-current alternators. It can also be used to determine if anything is draining the battery that you might have overlooked, which is useful when leaving the boat for long periods of time. One more thing to consider when using a voltage meter. Somtimes when there is a high current draw, such as a starter motor engaging, a weak battery will drop in voltage to a low value, i.e. 9.5 volts, which may not be enough voltage to fire an ignition system. This is a case where voltage can vary, although we like to think of it and want it to always be a constant 12-14 volts. Think of it like this. Amps are the amount of electricity and volts are the pressure of electricity.

 

[Jango]

Re: volts vs. amps.

Another way to look at it is:<br /><br /> Amps is like the size of a water pipe, and<br /> Volts is the water preasure

 

[MrBill]

Re: volts vs. amps.

There are three basic units in electricity...they are voltage, current and resistance. Voltage is measured in volts, current is measured in amps and resistance is measured in ohms.<br /><br />To reference the plumbing analogy...voltage is like water pressure, the current is the flow rate, and the resistance is like the pipe size, in that it restricts pressure and flow rate.<br /><br />The basic electrical equation indicates how the three items are related. Current (amps) is equal to Voltage (volts) divided by resistence (ohms).<br /><br />So that means: AMPS = VOLTS/OHMS<br /> <br />The other term we've all heard is Watts, electrical power is measured in watts. Watts is equal to the voltage times amps. <br /><br />Watts = VOLTS X AMPS<br /><br />This means that any increase in volts or amps provides greater power. For a good explanation of these terms and their meanings, simple home wiring books give good reference.

 

[allanwh]

Re: volts vs. amps.

All the replies are good ones. The analogy to a water hose is very good. basically the voltage is the electrical pressure in the system. Therefore when your boat is running and the alternator is charging the system voltage will increase from say 12.5 volts to around 14 volts. Therefore a voltmeter is a good indicator that your system is charging and holding a charge.<br />Under load when you turn on pumps , lights etc current ( amperes ) will begin to flow. An ammeter is a guide to how much current you are consuming . Therefore if you had a ammeter and it was showing a high reading with all appliances turned off it may indicate a fault or short somewhere in the system.<br />Hope this helps as too much explanation can get confusing.. As suggested in previous posts there are some good reference books available on this subject..

 

[crab bait]

Re: volts vs. amps.

if i were to have only one on my boat ...<br />i'd choose the voltmeter..

 

[SCO]

Re: volts vs. amps.

Your fuses cover the amps overload condition. You need the voltmeter to monitor the battery condition and charge function. I say the amps is like the amount of water flow in the pipe, not size (for clarity, I know what you mean Jango). The size of the pipe is analogous to the gauge of the wire. You dont want to force a gallon of water per second through a straw, just like you dont want to put 20amps of current through an 18 gauge wire. The wire will heat up. Current, measured in amps like water flow measured in gpm, is the amount of charge flowing per second. The charge is real live electrons flowing through the wire like water through a hose.

 

[mellowyellow]

Re: volts vs. amps.

all very good info guys... sounds like amp guages<br />aren't needed on a boat. thanks to all that replied!<br />regards,<br />M.Y.

 

[ODDD1]

Re: volts vs. amps.

Mellow, the problem with amp guages is that all the power the alternator puts out must run through a wire to the guage and then all the way back to the battery before it can do any good...usually a run of more than 40 feet....the longer the run, the more voltage drop you get, the less actual power you are getting out of the alternator....the other issue is the increasing output of marine alternators....wire size increases, as well as weight.....this all can be eliminated with a voltmeter...

 

[petryshyn]

Re: volts vs. amps.

mellowyellow<br />As you are aware, ammeters and voltmeters are both used for monitoring charging systems. The truth of the matter is, each one tells us pertinent information, but neither one tells it all.<br /><br />>Voltmeter tells us about the charging system:<br />*low voltage means its not functioning<br />(or we have high system load current)<br />*high voltage means the regulator is bad (or unregulated)<br /><br />>Ammeter tells us more about battery condition:<br />*high current means the battery is low in charge<br />(or the charging voltage is too high)<br />*low current means the battery is up in charge<br />(or the charging voltage is too low)<br />*the ammeter also tells us the current draw of the accessories when the engine is not running.<br /><br />The truth of the matter is, we really need both to get a full picture of what is going on. One gauge does not tell the whole story without the other. Knowing the voltage doesn't tell us system load or battery condition. As ODDD1 says, series ammeters add resistance to the charging circuit. Shunt type ammeters do not and are more accurate. Voltmeters are used because they are cheap and easy to install. Since they are connected after the ign switch, they aren't dead accurate if any accessories are being used. They SHOULD be connected directly across the battery.<br /><br />If you are a fanatic, you need both.....<br />

 

[wonko]

Re: volts vs. amps.

on a side note, good to see you back schematic, it's been a while.

 

[mellowyellow]

Re: volts vs. amps.

hey Fanatic (schematic), what is the difference between shunt and series?<br />can you tell by looking at the gauge?<br />what promted this question is the old box of<br />gauges I found in the attic which I think came<br />from an old chris craft. they are Simpson brand,<br />say alternating current at top and Amperes below<br />with the numbers 1-5, w/10 increments btw.<br />I thought maybe I would be able to use 1,<br />but needed to know what the readings would mean.<br />ok, so I have too much time on my hands...LOL<br />PS. I have 3 extras... anyone want 1?<br />thanks,<br />M.Y.

 

[jhreed]

Re: volts vs. amps.

From my limited experience with gauges, I would <br />want one of each. The current-one to watch "too much load" and the voltage-one to watch for "too <br />much voltage" that might damage radios, fish finders, GPU's, etc. If I had to take one or the <br />other I would choose the voltmeter... At least you would know that the charging system was working, or trying to work.

 

[petryshyn]

Re: volts vs. amps.

mellowyellow<br /><br />The shunt type ammeter is nothing more than a sensitive voltmeter which measures the voltage drop across a calibrated conductor (shunt). Sometimes an existing wire from the alternator to the battery is used as a shunt.(it remains in the circuit unaffected) <br /> A series ammeter is intrusive as it has to be connected in the charge line "between" the alternator and the battery. <br />Sounds like the meters you have are of an industrial nature and are for a/c current. Put an ohmemeter across them and see if the needle moves on the gauge. If it does, its an external shunt type....