Ammeter always negative

[Boat]

Hey guys, I'm confused about the readings on my ammeter. A little history here. I just purchased the boat. The PO had mentioned that the start battery was weak and possibly failing. No mention about house batteries. After inspecting and being unable to revive any of them, i replaced all of them. What i have is

2 group 31 for house connected parallel (115ah ea.) total of 230 ah
1 group 24 for starter 85ah

My panel, wiring, selector switch are all new.

My question is that the ammeter always shows to the negative when motoring. Even after an hour of motoring. Volt meter shows 14, everything is turned off on the boat, all lights, fridge, stereo. Only running the motor. Do I have a ground off or ????? I was under the understanding that it should go to the positive at some point soon after starting. Any help is freatly appreciated

[thatch]

Hi, Your ammeter is a polarity sensitive gauge. Is it possible that you reversed the leads during the re-wire process. If you are reading 14 volts, I suspect that this may be the problem.
Tom

[Boat]

The meter has always shown negative. From day one. I suspect maybe something is up with the wiring of the guage. Im going to check the wire and i believe it goes - oragne wire from ignition batt. One side of guage. Out other side to the output terminal of alt. battery replacement was straight up trade of the old ones. So unless the installer of the new breaker panel and selector switch mixed something up i believe the batteries are wired correct

[ndutton]

Why do you have both an ammeter and voltmeter? Usually we see one or the other, the voltmeter generally preferred.

[BunnyPlanet169]

My question is that the ammeter always shows to the negative when motoring. Even after an hour of motoring. Volt meter shows 14, everything is turned off on the boat, all lights, fridge, stereo. Only running the motor. Do I have a ground off or ????? I was under the understanding that it should go to the positive at some point soon after starting. Any help is greatly appreciated

You're correct in that it should show positive (charging) pretty much right after it starts, and then gradually head towards zero as your batteries charge.

If it behaves like this, but reversed (e.g. negative amps slowly going towards zero) then your ammeter is wired backwards.

Otherwise, and having replaced three dead batteries, I think I'd have the alternator load tested.

[Boat]

Why do you have both an ammeter and voltmeter? Usually we see one or the other, the voltmeter generally preferred.

I dont know why, i just got the boat so its what the PO had. Volt meter aacts normally, shows 14v. I took a meter to the batts while cruising and they all show between 31.9 and 14.3. Even after cruising on motor for four hours.

[Boat]

You're correct in that it should show positive (charging) pretty much right after it starts, and then gradually head towards zero as your batteries charge.

If it behaves like this, but reversed (e.g. negative amps slowly going towards zero) then your ammeter is wired backwards.

Otherwise, and having replaced three dead batteries, I think I'd have the alternator load tested.

Im thinking this route because it never gets to zero, but on this last cruise yesterday, it was always pegged to the negative, going to check the guage and pull the alternator i guess, unless i find something with the guage.

[ArtJ]

If the battery never goes dead, then it must be receiving a charge which
makes wires on ammeter suspect to being reversed. You can verify
charging by putting a voltmeter across the battery while running the
engine above enough rpm to initiate charging. If you see the voltage
measured to rise slightly above where it was without the engine running, then
the battery is being charged. This value depends on the specific
alternator as well as the current state of charge of the battery.
expect a small voltage difference a couple of volts max difference.

[sastanley]

Boat, As Neil was alluding to, I'd remove the ammeter altogether. A voltmeter at 14v while the engine is running tells you what you really need to know..the alternator is charging. There is some charging current lost in the run from the alternator to the ammeter and then back to wherever it connects for charging (common post on 1/2/all switch?? )

I would just eliminate it, and run the wire directly from the alternator to the common post (or wherever yours terminates at the other end of the ammeter)to get more juice to the batteries!

(I had my ammeter wired backwards once too, and it read negative while the engine was running....before I yanked it. )

[BunnyPlanet169]

I like having both, but I have a relatively low-power system (< 30A charging max). If you have a large enough wire and good connections, there generally isn't enough voltage drop to notice. That's a big 'if' however, with either factory or PO wiring.... And obviously, there are different good opinions from knowledgeable people.

I'm thinking this route because it never gets to zero, but on this last cruise yesterday, it was always pegged to the negative, going to check the guage and pull the alternator i guess, unless i find something with the guage.

In your case, the ammeter is telling you something useful. It may be that the ammeter is reversed. But if it's staying hard negative, then you probably need to look to the alternator. Maybe one bad diode.

[Boat]

Well into the lax arête and to the back of the panel. Holy cow! Gonna have to just remove it and start over. There is such a mish mash of wires and wire nuts I can't make heads or tails out of it. Is there a diagram of wiring from alternator to batts and etc? I have the one for the gauges but not anything else

[BunnyPlanet169]

Here's a good start for a basic, engine-only, alternator/battery/instrument/ignition circuit. This is the MMI diagram.

http://www.moyermarine.com/forums/sh...21&postcount=8

[romantic comedy]

I have both volt and ammeter. The ammeter will read negative when power is being used and the engine is off. It will read positive when the engine is running, and charging. If it never goes to positive, something is amiss.

[Carl-T705]

I don't know what you have going on here, but the amp gauge may not be wired into the alternator/ battery lead wire but merely a positive wire in the harness. Or the gauge is bad. An on the cheap check would be to remove the battery/ alternator wire on the alternator, wire in the gauge between the alt. and the batt. lead , start the engine and speed up the idle, this should read a charging signal, if it reads discharge, reverse the wires, if the needle still doesn't move the gauge is junk. The cheap amp meters are prone to failure and causing fires, get a good one rated to 75-100 amps .

[Boat]

I havent yet gotten into the wiring yet. Regular life is getting in the way of my sailing time i have found my alternator manual. It is a 90 amp prestolite 110-403. The iinsructions reccomend the use of an ammeter with wire running from alternator output through the guage and back to battery. It mentions wire guage of at least #6. It also says what the ammeter should be doing at various stages. Either a plus or negative charging rate. The more i read on it im thinking mine is either wired backwards or im discharging somewhere. Other than crossed wires what would discharge the batteries? When i fire the motor it is half way in the red. When i bring up the idle it goes farther in the red.