Volts or Amps..which do you watch?

[wilson!]

When trolling with a trolling motor. I heard somewhere that testing the volts has nothing to do with how much power is left. Can you have no volts but have amps and still run your boat?

I see so many voltage alarms being sold online such as:
http://www.batterystuff.com/battery-products/LOWBAT-XL.html

..so does this mean you have to watch your VOLTS on the lake or your AMPS??

Do i need an AMP METER AS WELL???

..or am I completely mixed up here?

 

[bruceb58]

Re: Volts or Amps..which do you watch?

Unless you can monitor amps and keep track of the exact elapsed time, measuring the amps is pretty much worthless. As batteries age and have gone through many charge/discharge cycles, the amount of capacity that a battery holds goes down so unless you also know that(which you can't unless you do a specific test for that) its also worthless. Battery voltage gives a very good indication of what percent level of charge your battery is at.

http://www.solarnavigator.net/battery_charging.htm

 

[John_S]

Re: Volts or Amps..which do you watch?

The amp meter will only show you what is being drawn at the given moment. It does not provide any indication of what is left in the battery. Even if the battery has dropped way down to 10V, current will be drawn as long as there is any load.

 

[Big Pete]

Re: Volts or Amps..which do you watch?

Unless you can monitor amps and keep track of the exact elapsed time, measuring the amps is pretty much worthless. As batteries age and have gone through many charge/discharge cycles, the amount of capacity that a battery holds goes down so unless you also know that(which you can't unless you do a specific test for that) its also worthless. Battery voltage gives a very good indication of what percent level of charge your battery is at.

http://www.solarnavigator.net/battery_charging.htm

I second this , absolutely correct ..and useful chart ..

 

[wilson!]

Re: Volts or Amps..which do you watch?

mama mia, the plethora of knowledge here astounds the masses (me)


Thank you much!

 

[wire2]

Re: Volts or Amps..which do you watch?

An easy way to envision it, compare an electrical circuit to a water system.

A large storage tank (battery) gives pressure at a tap into a hose at the bottom, (voltage).

Opening the tap allows water to flow (current)

As the volume of water is used up, the pressure at the tap will drop (less voltage), so the water flow is slower.

By Ohm's law, less voltage into a fixed resistance means less current. (a trolling motor will slow down)

When the tank is empty (dead battery) all flow (current) stops.

 

[Silvertip]

Re: Volts or Amps..which do you watch?

If your boat had an ammeter like some older ones did, that meter showed you the "rate" of charge or discharge which was meaningful but still had no bearing on whether the battery was accepting that charge or if it was, how close to full charge it was. The meter was calibrated -60/0/+60 or some other set of numbers but center was always zero. If the needle went to the minus side it said the electrical system was losing ground in that more current was being drawn from the battery than the generator/alternator was replacing. If the needle was in the positive area it said the battery was indeed charging since more current was available than was being used. The fact that the system was outputing more current than being used however does not mean the battery was actually accepting that charge. A voltmeter has more meaning since with the key on but engine not running, the voltmeter indicates "static" voltage. With the engine running voltage will rise above 12.6 (static voltage) indicating the charging system is working. If for example the voltmeter reads 13.6 with the engine running but when not running the battery reads less than 12.6, that means the battery is either bad or the engine has not run long enough to top off the battery.