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Old 27-10-2018, 06:49   #1
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Why an Amp meter there?

There is an Amp meter on the starting control panel of my 1985 Catalina 27. (The other functions of this cockpit panel are the ignition key, glow plug push button, starter pull, rpm, tem and fuel gauges and engine kill lever).


Why an Amp meter there?


I understand that an Amp meter is to measure the flow of current in a given circuit. But at that location? Which circuit? What should it tell me?


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Old 27-10-2018, 07:07   #2
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Re: Why an Amp meter there?

Is this a Universal diesel? My previous boat had a 5411 and did have an amp meter on the panel. It showed both current in and out of the batteries. Would show the big draw when I used the glow plug before starting and would show current into the batteries when the engine was running and charging.
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Old 27-10-2018, 07:29   #3
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Re: Why an Amp meter there?

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Originally Posted by JimsCAL View Post
Is this a Universal diesel? My previous boat had a 5411 and did have an amp meter on the panel. It showed both current in and out of the batteries. Would show the big draw when I used the glow plug before starting and would show current into the batteries when the engine was running and charging.




Thanks... Yes it's a Universal M 18 (15 HP)
Your answer makes a lot of sense..... but who is watching that gauge with a barely moving needle when you concentrate your attention on starting your motor?
Have you ever paid attention to that gauge?
Thanks
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Old 27-10-2018, 07:56   #4
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Re: Why an Amp meter there?

What the gauge is measuring is determined by the location of the shunt.

If the amps displayed changes from normal, it can be an indicator something is wrong, with the alt or the bank it's charging.

Or can be crude indicator that you drew the bank SoC down further than usual since the last time you started up the engine.
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Old 27-10-2018, 08:02   #5
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Re: Why an Amp meter there?

Not directly related to your question, but you might find this article of interest : https://marinehowto.com/universal-di...rness-upgrade/
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Old 27-10-2018, 08:08   #6
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Re: Why an Amp meter there?

This type of ammeter was very common back in the day in boats, airplanes, trucks and many stationary power units. It gives you a true indication of the charging status of the alternator, you don't need to wait until voltage drops off to see there is a problem. These meters were direct read meters placed in series with the alternator output wire. Most of these alternators were 30 to 45 amps so this was a practical solution.
As far as the meter pegging out during start up it sounds like something isn't wired right. Typically the meter is wired inline to only the alternator output, between the alternator and the battery. No current should be present on this wire during cranking.
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Old 27-10-2018, 09:03   #7
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Re: Why an Amp meter there?

dave948 is the most right in this thread.
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Old 27-10-2018, 09:37   #8
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Re: Why an Amp meter there?

Those Universal ammeters were famous for using wire that was too small and would often burn the wires up. Worth upgrading.
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Old 27-10-2018, 09:40   #9
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Re: Why an Amp meter there?

It may show (depending on the actual shunt location) either the in-flowing current produced by the alternator, or the out flowing total current from the bank of batteries. If it jumps out during engine start, it is most possibly in the second position.
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Old 27-10-2018, 11:36   #10
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Re: Why an Amp meter there?

To make matters worse, Catalina runs the charging circuit from the alternator to the panel then to the batteries using generally undersized wire.
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Old 27-10-2018, 12:05   #11
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Re: Why an Amp meter there?

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Originally Posted by CelestialMelody View Post
To make matters worse, Catalina runs the charging circuit from the alternator to the panel then to the batteries using generally undersized wire.

This is the actual issue, and it's a BIG one if you intend to do any cruising away from dock and depend on your alternator. Small wire, sh*tty connectors, and no reason to run power all the way there and back again.


Read these:


Critical Upgrades CRITICAL UPGRADES - DO THESE OR ELSE!!!


This is for M25 enines, but the issues are identical.


Here's the Fix: one copies an earlier Maine Sail link


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Old 27-10-2018, 12:26   #12
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Re: Why an Amp meter there?

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Not directly related to your question, but you might find this article of interest : https://marinehowto.com/universal-di...rness-upgrade/
Glad you posted the link to this. THIS IS IMPORTANT!! The ammeter and the "trailer" connectors are potential problem areas and should be checked and fixed if you have them.
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Old 28-10-2018, 09:28   #13
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Re: Why an Amp meter there?

Everyone posting replies about the shunt... Yeah it doesn't have one. It is a direct read meter from the factory. 100% of the alternater current passes through the meter.
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Old 28-10-2018, 09:41   #14
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Re: Why an Amp meter there?

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Everyone posting replies about the shunt... Yeah it doesn't have one. It is a direct read meter from the factory. 100% of the alternater current passes through the meter.

Every ammeter has a shunt. It's how they work. Some are simply built into the meter, others are external to the meter itself.


Ammeters & Shunts 101: Ammeters & Shunts 101
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