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Amp meter?

5789 Views 28 Replies 11 Participants Last post by  GaryHLucas, 
M
Does having an amp meter in the charging system increase voltage drop, In other words will an amp meter increase resistance in a charging system?
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Stillraining
Not enough to worry about..all the new finagled multimeters now include an Amp meter..ie..link 10/20 ect. Their rated draw is .o something.
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M
I have a old style analog amp meter as part of my engine gauges I like it and want to keep it. Is this also true of this gauge?
thanks
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Maine Sail
motion300 said:
I have a old style analog amp meter as part of my engine gauges I like it and want to keep it. Is this also true of this gauge?
thanks
Click to expand...
Bypass it and replace it at teh engine panel with a standard volt meter then add a true battery monitor like a Victron or Xantrex Link below decks.

The problem with your set up is that the entire charging current from the alternator is running through 20 some odd feet of 12 ga wire, if it is the typical system I am thinking of. Forcing 100 amps through 20 feet of 12 ga wire is never a good idea. I use a 6 ga wire directly from the output post of my alt directly to my house bank which is only 4 feet way..

The Catalina 34 association has lots of info on this upgrade as many Catalina's with Universal Diesels came this way.
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Stillraining
I would say very close...or in other words a non issue compared to the value of information that meter will provide you.

I have in my tool box a amp meter you hold over a cable to read the current draw..I doubt it draws any current from the system to measure it...but it might be an amp or two incorrect it its reading compared to an in line meter is all.
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B
Ammeters themselves generally present a very low resistance at their rated values. They use either an internal shunt (like many of the 30-0-30 or 60-0-60 Stewart Warner models) or an external shunt (like most higher-amperage models).

But, I agree it's a good idea to rework the system, not so much because of the ammeter itself, but because of the typically too-small wiring and the lengthy run from the alternator back to the panel and then, eventually, on to the battery.

To get the most from your alternator, it's good to oversize the cable directly to the batteries to ensure a very small voltage drop.

Bill
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M
I guess this has answered my question I have what look to be an old stiff 8ga wire running from my alternator I have purchased 30; of 4ga tinned wire, winter project
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N
Motion, although not a hightech solution, just the re-wiiring with larger gauge, will freshen up your system and surely will bring a better charging compared to what you have today. Good luck.
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M
negrini said:
Motion, although not a hightech solution, just the re-wiiring with larger gauge, will freshen up your system and surely will bring a better charging compared to what you have today. Good luck.
Click to expand...
Thanks, Thats the plan 4ga wire, a large frame alternator and a smart reg. OH yea I just recieved my new 12volt refrigerator to replace the 110 volt unit that ran off the inverter
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roline
I added an amp meter to my engine panel that was a 500 amp shunt with a low voltage digital meter, 50 millvolt. I had more voltage drop from the battery cables than the shunt. I now know max amperage from the alternator and how quickly it drops. For a 200 amphr bank it will run at 45-50 amps for a few minutes and then drops off to under 35 amps and then lower.... So upgrading to a 55 amp from a 35 amp alternator helped just a little for quicker charge.
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mitiempo
A smart reg will let your alternator produce more during bulk charging stage - when the bank is at 50 to 80% of charge. But ultimately an ammeter doesn't give you nearly as much information about your batteries as a dedicated battery monitor like Xantrex Link products or similar. The ammeter will tell you how large the flow is in either direction but the link will tell you % of charge or discharge which is much more valuable. It will also let you find out accurately how many amps every single item on board draws and adjust accordingly.
Brian
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Omatako
Am I missing something?

I have the main output from my big alternator going through about 4g wire to one side of a shunt that is 2 feet from the alt. The wire on the other side of the shunt goes another two feet to the battery bank. The two wires that run to the ammeter and back to the shunt are probably 20g and about 7 metres. The ammeter is an analogue 0 to 200 amps

The alt regularly puts out 140 amps after the Xantrex runs into orange lights (80% discharge).

Nothing gets hot (or even warm), everything is seemingly working OK, should I be worried about something.
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M
Does not sound as though you have any problem. My set up puts the amp meter maybe 10-15' from the altenerator, I need to up grade my wireing
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B
Andre,

Yes, I'd be a bit worried about that AWG4 wire carrying 140 amps, even over the short 8' round trip distance. That's theoretically a 2.9% voltage drop (or about 0.4V), assuming everything is working right: tight, clean connections everywhere.

AWG4 is usually rated for 70amps DC. With a 140-amp alternator or battery charger, I think I'd want considerably larger cable (say 1/0 or 2/0) in order to avoid as much resistance as possible and ensure my house battery bank was receiving a maximum charge.

JMO,

Bill
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Bene505
Amp meters are really voltage meters across a VERY small resistance - like a bar of metal. That resistor is so conductive that it creates a tiny voltage across it. Yes, there is current flow to the needle of the meter, but in terms of wasted power, there is very little.

Ask yourself "how much does this meter heat-up when it's being used?" and you'll know how much power it uses. Very little.

.... At least on our boat anyway.

Regards,
Brad
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mitiempo
The ammeter takes virtually no power out of the charging system. The shunt continues the charge circuit from alternator to battery bank. The two small wires measure amperage and feed the meter. The shunt shown is a 50mv/500amp, when 500 amps is going through it the small wires fees 50mv to meter - so no heat. As far as wire gauge, 8' return trip is about 3% drop with 4ga, 2% drop if the wire is 2ga. I would also change to a heavier wire, maybe 1/0 for minimal drop. The wire calculator gives 2% loss with 1/0 handling 280 amps. AWG by wire length/amps calculator
Brian

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Bene505
mitiempo said:
The ammeter takes virtually no power out of the charging system. The shunt continues the charge circuit from alternator to battery bank. The two small wires measure amperage and feed the meter. The shunt shown is a 50mv/500amp, when 500 amps is going through it the small wires fees 50mv to meter - so no heat. As far as wire gauge, 8' return trip is about 3% drop with 4ga, 2% drop if the wire is 2ga. I would also change to a heavier wire, maybe 1/0 for minimal drop. The wire calculator gives 2% loss with 1/0 handling 280 amps. AWG by wire length/amps calculator
Brian
Click to expand...
If you think of it as this "The two small wires measure voltage and feed the meter." Then it's can be a little easier to visualize.

Excellent post.
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M
is it practical to use a shunt with an old style analog dash mounted amp meter? Would this work? If so where would one get a shunt?
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Maine Sail
Guys..

I'm afraid we've missed the point a little.

The problem with the engine panel ammeter is not about a heavy duty 500 amp shunt, or its resistance, it is about the output of the op's alternator running through 15+/- feet of small gauge wire to the panel then 15+/- feet back to the battery switch. This makes for a 30+/- foot round trip voltage dropping run. Follow me here, the alts output leaves the alternator and from there goes all the way to the ammeter in the cockpit. Then, from the ammeter all the way back to the to the battery switch.

The voltage drop is not necessarily due to the cheap gauge style ammeter but rather the ridiculously long round trip run with small gauge wire for the charging circuit..

motion300 said:
is it practical to use a shunt with an old style analog dash mounted amp meter? Would this work? If so where would one get a shunt?
Click to expand...
No it is not practical as these meters use their own internal shunts.

These dash mounted Teleflex, VDO etc ammeters are HORRIBLY in-accurate. I have come across dozens of them that never even change and always show a steady output like a temp gauge..:confused:

Photo courtesy Defender

This = JUNK!

You will be far better off to get a real battery monitor, like a LINK or a Victron BMV series, that is highly accurate, and replace the ammeter with a volt meter. Volt meters are $22.00 - $26.00. Hell for the price of the wire you'll need to keep your ammeter and wire it correctly you could have a REAL battery monitor that will tell you far more than just amperage. Volt meters are $22.00 - $26.00. Besides teh weight and lug sizer of 1/0 wire will NOT bolt to the back of your ammeter. Hell 1/0 lugs are bigger than the back of the meter...

This = Excellent Replacement for Ammeter


All you really need to know in the cockpit is that you are producing sufficient voltage and that your voltage regulator is not fried.

Again your problem IS the long wire run, NOT the ammeter. You stated earlier that you bought 30' of 4 AWG and you currently have what looks to be 8 AWG.

If you have a 100 amp alt, you may actually have bigger, you will need 30' of 1/0 wire to hit a 3% voltage drop. This is a LOOOOOOONG way from 8 AWG. Again, ditch the 30' run and crappy gauge mounted ammeter and install a real battery monitor. Wire your alt directly to the bank or batt switch, maybe a 6' run, vs. 30' or another way to llok at it is 6 AWG vs. 1/0 AWG. Your talking about $150.00-$200.00 worth of wire for a cheesey, inaccurate ammeter that only costs $25.00..?
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M
Ok so I need a battery monitor, I don't trust xantrex quality so I am thinking Victron, is this a good device?
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