Amp meter showing draw

Hello, any suggestions will be appreciated.

I have a '79 (org. set-up) Mercruiser 260 with a Motorola 3 wire system, upgraded to a 68 amp Delco, both red and black leads are correctly pluged in to the bullet leads on the harness, sens. and exc. Alt. is putting out volts at idle-14.2 or so, batteries are holding better than 13v on load test, ok here is the crazy, @ idle AMP meter needle sets at 0, start turning on acc. needle shows neg. draw all the way to-28 or so amps, however the alt. is still indicating a positive charge with voltmeter on battey post and will increase volts with a rev of the engine. Any thoughts? have not been out since this was discovered, hard to paddle a 28 footer in the Mississippi

Re: Amp meter showing draw

Sounds like normal operation to me.

You will see very little drop in voltage until the demand exceeds the supply. In this case your 28 amps is roughly a 1/3 of your 68 amp capacity. I wouldn?t expect to see a voltage drop until you put a much higher demand on your output.

Re: Amp meter showing draw

Thank you for your response, I agree, however I have always seen or understood that if the alt. was doing it's job that the meter would show a slight dip and then a recovery back to zero or even a slight increase in output if reved up, this meter is showing -draw at any rpm if these acc. are used at all

Re: Amp meter showing draw

It all depends on "where" in the circuit the ammeter is installed. If the ammeter is inserted in the "boat harness" (the red wire between the battery and the console/breaker panel) it will never read "+" (or charging) even though the alternator is indeed working normally. In that configuration the ammeter does not "see" the charging current. An ammeter is a two-way meter in that it must be installed so it can see not only what is being drawn from the battery but also what the alternator is putting back into it. The difference between the demand or load and the alternator output is the charge rate. If the loads are taking 28 amps and the alternator is a 68 amp unit, you would see a positive charge rate determined in part by the regulator. With the engine off yoju would see a negative 28 amps because nothing is being fed back to the battery to make the needle swing into positive territory. Therefore the meter needs to be beween the positive post of the battery and the load on the boat circuit and the alternator output needs to go to the load side of the ammeter as well. Negative on the meter goes to POS on the battery. The load goes to the POS on the meter. The alternator output goes to the POS on the meter. A voltmeter will read charging system voltage regardless where you measure it and it has no bearing on what the ammeter says. I suspect the ammeter is wired into the boat harness correctly but the output of the alternator is not. It is very likely going directly to the battery via the large battery cable and it really needs to go to the load side of the ammeter via the charging lead that is normally connected to the starter solenoid then to the battery. This is exactly why voltmeters have become the better choice. It eliminates a whole bunch of heavy gauge wire. I guess I'll need to diagram this.