Using a Volt meter to determine batter level? How to wire it properly accuracy?

[scbasschaser]

I have a 25merc electric start outboard w/o an alternator or internal charging system on an older jon boat. My electronics are powered by a stand alone 12v deep cycle interstate marine battery that I recharge after each use. I run a depth finder, trolling motor and lights and occasional cigarette lighter accessory off this main battery. Mercury said I could use a standard volt meter and watch as the gauge go down in volts to determine how much charge my accessories are using and would like an indash mount for looks. They are sending me the part and the wiring diagram (I hope) but would like some input if this is the best route for a simple look of what my battery is doing after several hours on the water.

Also, I don't disconnect when not in use and since I have power switches for each device I confused about why undo you battery wiring each time. Sounds like overkill to me? I have several things wired to my battery and can't undo them each time.

 

[Bondo]

Re: Using a Volt meter to determine batter level? How to wire it properly accuracy?

Ayuh,... So long as the volt meter is hooked up to the system, it'll show the voltage of the system....

'n whether you disconnect the battery by removin' the wires, or turnin' off switches, Don't matter, so long as any possible draw is eliminated...

 

[scbasschaser]

Re: Using a Volt meter to determine batter level? How to wire it properly accuracy?

Ayuh,... So long as the volt meter is hooked up to the system, it'll show the voltage of the system....

'n whether you disconnect the battery by removin' the wires, or turnin' off switches, Don't matter, so long as any possible draw is eliminated...

Thanks Bond-o, If the gauge says 8v to 18v and my battery is 12v and assume that 12v is full, do you know at what volt level I'm getting close to the battery being on zero. Say I'm out at night and we drain it down to where I have no lights, that could be fairly big issue. Any thoughts? Should it go directly to the battery or ignition switch. Not sure I understand the difference?

 

[Bondo]

Re: Using a Volt meter to determine batter level? How to wire it properly accuracy?

Ayuh,... A Fully charged 12v battery will show 'bout 12.5v....

Yer lights will probably still work at 8v, but will be dim, 'n you'll be pull startin' yer motor...

 

[scbasschaser]

Re: Using a Volt meter to determine batter level? How to wire it properly accuracy?

Ayuh,... A Fully charged 12v battery will show 'bout 12.5v....

Yer lights will probably still work at 8v, but will be dim, 'n you'll be pull startin' yer motor...

Ok, this is my first boat, used and being tinkering on it for about 6months and trying to learn good defense before running a long distance from the take off. Good news is I can pull start the motor.

Any thoughts on wiring to directly to battery or ignition. Most of the switches I rewired are pretty simple and plan to have a switch dedicated to the volt meter to flip on and check it and then turn it off.

 

[JB]

Re: Using a Volt meter to determine batter level? How to wire it properly accuracy?

A voltmeter will not accurately indicate a battery state of charge except when the battery is under heavy load. Only a hydrometer can do that. The hydrometer tests one cell at a time.

 

[scbasschaser]

Re: Using a Volt meter to determine batter level? How to wire it properly accuracy?

A voltmeter will not accurately indicate a battery state of charge except when the battery is under heavy load. Only a hydrometer can do that. The hydrometer tests one cell at a time.

Thanks JB, My goal is to get a "close read" since I'm just worried about the electronics and how much time before the battery is totally drained on my jon boat. Just to let me know to pay attention of how much time I have left.

My other issue to is have on/off switch that I can quickly see without the ignition key what's going on so need some ideas on wiring this? Tx!

 

[Bondo]

Re: Using a Volt meter to determine batter level? How to wire it properly accuracy?

My other issue to is have on/off switch that I can quickly see without the ignition key what's going on so need some ideas on wiring this?

Ayuh,... The circuit would be, from the battery, to the switch, to the gauge, to the battery....

 

[Silvertip]

Re: Using a Volt meter to determine batter level? How to wire it properly accuracy?

You do not wire to the ignition switch in your application. The voltmeter draws very little power and can be left on without significantly affecting anything else. However, run a wire from the positive terminal of the battery to one terminal of a SPST (single pole, single throw) switch. From the other terminal on the switch go to the + terminal on the meter. The negative terminal on the meter goes to the negative terminal on the battery. Done! And by the way -- if you are running the battery down to 8 volts it is essentially dead and continually doing this will drastically shorten battery life.

 

[Scott Danforth]

Re: Using a Volt meter to determine batter level? How to wire it properly accuracy?

a fully discharged battery will read 12.0 volts. a fully charged battery will be around 14.0 - 14.5 volts. 2.0 volts per cell is discharged, 2.4 volts per cell fully charged. taking a battery below 12 volts will shorten its life considerably.

 

[scbasschaser]

Re: Using a Volt meter to determine batter level? How to wire it properly accuracy?

Thanks Mates, your advise should save me some dough in the long run! I had no idea about draining a battery down below 12 would kill the life cycle. Really learned a lesson here. I got the wiring down easy enough. Sounds as if I need to think about another battery just for the trolling motor. Again, thanks much.

 

[Silvertip]

Re: Using a Volt meter to determine batter level? How to wire it properly accuracy?

Disaree that a fully charged battery reads 14.5 volts. It will under one condition -- that being for a very short period after a battery charger is removed. It's static voltage when charged is 12.6 volts.

http://www.autobatteries.com/basics/voltage1.asp

 

[scbasschaser]

Re: Using a Volt meter to determine batter level? How to wire it properly accuracy?

What's the easy solution to keeping a fresh battery. An extra battery? The volt meter arrives today and curious to see how much charge stays on the battery after a day at the lake. Do they make a charging device that will connect to 25hp motor would really solve my problem but might be a pricey add-on.

 

[Silvertip]

Re: Using a Volt meter to determine batter level? How to wire it properly accuracy?

If the engine doesn't have a charging system -- which most rope starts don't, then the only choice is to install an on-board charger which you plug into house power at the dock. Adding a separate battery solves nothing since it too must be charged. Batteries need to be charged immediately after use since leaving them in a partially discharged state shortens their life. Some outboards have an AC (alternating current) output that can be used to run non-electronic devices such as lights which don't care if they are powered by AC or DC current. To charge a battery however, that system needs a rectifier that converts AC to DC current. You can check with your dealer if such a kit is available for your engine but it may be much more pricey than an on-board or portable battery charger. Even if a charging kit is available, for a motor like yours the output would be very low and unless you run wide open for hours at a time, would never fully top off a deeply discharged battery. My vote is for the portable or on-board charger. Simple, inexpensive (relatively) and no wiring to worry about.

 

[vogelfish]

Re: Using a Volt meter to determine batter level? How to wire it properly accuracy?

What exactly are you running off this battery? If you're not using it for starting or running a trolling motor - a standard 12V "car type" battery in decent condition should power your depth sounder, for quite a long time. It's all about the load you put on it.

 

[Silvertip]

Re: Using a Volt meter to determine batter level? How to wire it properly accuracy?

I just read your first post and in it you say this motor has electric start. As such it probably has a charging system. So how do you start this motor if it has electric start. And if you are not using the battery to power the starter -- why on earth not? Even if it didn't have a charging system it still beats pull starting. The battery could simply be charged at the dock with a portable charger. If you are looking at the engine for an alternator and don't see one, that's because it is under the flywheel and uses a stator rather than a belt driven alternator.

 

[M9.9]

Re: Using a Volt meter to determine batter level? How to wire it properly accuracy?

Hi all, You might look up all the power consumption specs (amp/hr) of the lights and other items you use then multiply each by the average amount of time you use them; or keep a mental note of how long they are on. Either way, fully charge your battery and check daily while not in use for voltage drop, ie see if it's holding a full charge. There will be some drop but when sitting in average temperatures it should'nt be more than.5 volts or below 12 volts (in 10 days (if anyone else can expand on how long a good batt charge should keep at or above 12v please post)).

 

[scbasschaser]

Re: Using a Volt meter to determine batter level? How to wire it properly accuracy?

I just read your first post and in it you say this motor has electric start. As such it probably has a charging system. So how do you start this motor if it has electric start. And if you are not using the battery to power the starter -- why on earth not? Even if it didn't have a charging system it still beats pull starting. The battery could simply be charged at the dock with a portable charger. If you are looking at the engine for an alternator and don't see one, that's because it is under the flywheel and uses a stator rather than a belt driven alternator.

Thanks again, SUCCESS! I got the volt meter hooked up to the switch and it pulled just below 13 on the gauge engine off. I called Mercury dealer locally and he verified that the two cables running back to the battery are the charging system. He also sold me the 27series battery which is good for both trolling and cranking so I should be good. Whew! Best part I know exactly what's under the hood and that it is wired properly.

 

[soggy_feet]

Re: Using a Volt meter to determine batter level? How to wire it properly accuracy?

I just read your first post and in it you say this motor has electric start. As such it probably has a charging system.

FYI, not necessarily so. I have a '57 Johnson Super Seahorse. Electric start, no alternator.

 

[Don S]

Re: Using a Volt meter to determine batter level? How to wire it properly accuracy?

FYI, not necessarily so. I have a '57 Johnson Super Seahorse. Electric start, no alternator.

He has a 25 hp Merc, not a '57 Johnson Super Seahorse. Most outboards with charging systems don't have alternators.