Ammeter installation

[Roger Long]

If I want to start my long journey towards the perfect electrical system with the baby step of installing an ammeter, is there any reason why I can't wire an external shunt type into the negative battery lead just before the batteries? The way my panel is built and my engine room laid out, that would be easy to do. Putting it on the positive side, just after the battery switch, would mean major panel reconstruction.

 

[joker460]

Most of the Battery Monitor devices have the shunt installed on the negative side. So it will work fine that way.

That's the way I installed it.

 

[Maddog]

Are we talking about a simple amp meter that is part of your insturment cluster. One that registers fro -60 -0- +60 amps? I have mine wired to the output of my alternator so I can roughly, loosely quistmate how many amps my house bank is drawing while the engine is running.
Is your question more about a battery monitor than an amp meter?

 

[Stu Jackson]

No reason you can't on either the + or - side. For most recreational boats, the amps going through on the DC side the amperage is rather low (like, when do you have ALL of your DC loads on at once?) so that a Blue Seas 0-25 A meter with an INTERNAL shunt will work just fine. Since all the current is flowing through it, you'll need good sized wires if you go that way. If you use an external shunt, then the wires from the shunt to the meter itself can be small.

http://c34.org/bbs/index.php/topic,6032.0.html

 

[Roger Long]

Is your question more about a battery monitor than an amp meter?

A battery monitor is probably down the road unless the final bill for all the other refit items turns out to be less than expected. No room outside at the panel for an ammeter but I thought I might mount one inside near the electrical panel so I can start getting an idea what my actual electrical consumption is. I can get a 30 amp unit and shunt for under 15 bucks at a local electronics distributor vs. nearly 80 bucks for a Blue Sea 50 amp unit. Both + only.

Question: Is it OK for the ammeter to peg when the engine is starting or will that eventually screw it up? If it has enough scale range to handle starting, it won't be very accurate for other use.

While researching in my engine manual to try and find out how much the starter might draw, I ran across this interesting comment:

Since an alternator is used on this engine, when charging with a charger, always disconnect the battery (+) cable to prevent destruction of the diodes (Before disconnecting the (+) battery cable, disconnect the (-) cable).

My shore power battery charger is directly connected to the batteries (actually at the battery switch on the lugs the battery cables attach to). During the summer I lived aboard in the marina, I used to run the charger while lights and things were on. I never had any problems with the alternator.

What's up with this?

 

[Maine Sail]

Roger you'll want a shunt and meter capable of starting loads if installing this shunt at the battery. An alternative is to place it at the panel negative and capture your house loads but not starting loads. Unless you have an inverter or windlass you would not likely see loads of more than 30A..

 

[Roger Long]

An alternative is to place it at the panel negative..

Thanks, I should have thought of that. I can get to that cable easily.

What about the alternator diode thing? I don't imagine that Endeavour or Yanmar contemplated a boat like this having an on-board charger back in 1980. Have I been heating up and stressing my alternator diodes since 2005?

 

[Maine Sail]

Thanks, I should have thought of that. I can get to that cable easily.

What about the alternator diode thing? I don't imagine that Endeavour or Yanmar contemplated a boat like this having an on-board charger back in 1980. Have I been heating up and stressing my alternator diodes since 2005?

Nearly every boat in existence is wired that way and diodes just don't blow from that. They blow when you disconnect the load from them while charging by passing through the OFF position on the battery switch..

 

[Stu Jackson]

Roger, I don't see where that quote came from? I agree with MS, it sounds fishy to me.

 

[Roger Long]

I don't see where that quote came from?

It's from the Yanmar Service Manual from my 2QM20. I never heard of such a thing either so I was pretty surprised to see it. The alternator is a Hitachi.

The manual for this 1979 engine was written before CYA was as common as today but maybe it was a hedge against someone hooking on one of the big, cast iron, steam powered, battery chargers that were common at the time.

 

[Bob Mack]

Roger:

A quick thanks for your link to your prior articles, especially enjoyed your Vinyard voyage.

If installing an ammeter, have you considered a guage such as a Xantrex XBM, currently a Linklite, They use a similar shunt on the neg before the battery bank, but you get so much more info than from an Ammeter alone. Have it on my main panel and use it daily to monitor my solar panels and battery charge status.

 

[Roger Long]

have you considered a guage such as a Xantrex XBM, currently a Linklite,

Yes, but maybe not this year. We'll see after all the other bills come in. I can buy the ammeter and shunt for under 15 bucks if I don't want the packaging I throw away to say "Blue Sea" on it. At this point, I primarily want to run 20 hour tests on my batteries and start getting a handle on what my actual electrical usage is.

BTW, the ammeter was an important instrument when I was flying even though it was a tiny toy without even any numbers. As ammeters go, it was the equivalent of those little compasses they give away in Cracker Jack boxes. The master switch on most airplanes st a double switch. One side turns everything in the airplane on and off similar to a boat's battery switch. The other side turns the field to the alternator on and off and I'm thinking such a switch would be a good addition to a boat.

High compression aircraft engines really suck the amps starting up and the batteries are small. Having the alternator out of the circuit frees up a several amps for starting. This could help if you were trying to get a boat engine going on the last dregs of a battery.

After starting the aircraft, we would note the ammeter needle position, turn on the alternator, and then watch the needle move back to its normal position over about half a minute. This confirmed that the charging system was operating normally and the starter wasn't stuck engaged and turned into a generator that would fry tens of thousands of dollars of avionics. Even without numbers, we got used to the exact behavior of the needle and could spot any change in the way the charging system was behaving.

A field switch on a boat would also be a good thing to have if you found yourself in an overcharging situation due to regulator failure and couldn't safely stop the engines.

The regulators we had in the plane were the old "doorbell buzzer" type until just before I stopped flying because the FAA makes it incredibly difficult to bring in new and improved technology. Small aircraft lag about 30 years. It's amazing they even permit GPS.

 

[Bill Roosa]

Starting down the road to the perfect?? electrical system???

Well, first off I'm putting you on my prayer list.
Do you have the end state in mind? Always begin with the end in mind.
Then buy the bits and pieces to achieve the whole.
On a limited budget you do not want to buy stuff only to buy it again because the next upgrade already has one in it. A good example being a battery monitor. It has an ammeter in it. Buy an ammeter now and when you upgrade to the battery monitor you get to throw your old ammeter away. Another example is an inverter charger bought after you bought a new charger and new inverter. Just kinda expensive way of doing things. Sometimes it is much cheaper to wait a while and save your money to get the final "perfect boat" part solution.
FWIW

 

[Maddog]

Maine - Could you post a simple schematic showing how a simple ammeter wired onto the negative would work. I am an idiot, but it sounds like Roger is using a simple dash gauge and shunt to measure amp usage, not amps charging? Both?
I'm not bad with DC power once I understand the concepts and goals. I haven't killed myself yet.

 

[Maddog]

I think I'm getting the concepts and the goal.
Is this the unit that would be a half step to getting a full monitoring system?
http://bluesea.com/category/6/23/productdocs/8248

 

[Stu Jackson]

Maine - Could you post a simple schematic showing how a simple ammeter wired onto the negative would work. I am an idiot, but it sounds like Roger is using a simple dash gauge and shunt to measure amp usage, not amps charging? Both?
I'm not bad with DC power once I understand the concepts and goals. I haven't killed myself yet.

MD, if you read my link suggested in my earlier post (Reply #4), that answers your question.

 

[Stu Jackson]

I think I'm getting the concepts and the goal.
Is this the unit that would be a half step to getting a full monitoring system?
http://bluesea.com/category/6/23/productdocs/8248

Yes. It's digital not analog, same connections though.

 

[Roger Long]

Maine Sail stopped by the boat this morning with his battery tester and it indicates that the batteries are about 25 - 40% diminished in capacity which isn't too bad for 2005 AGM's that haven't had a good, solid charge since last summer. My light loading and frequent long legs under power have kept them reasonably happy. For cruising around the civilized coast, I could probably go another season or two with them but AGM's also tend to die suddenly with less warning than wet cells.

All this has raised my consciousness to the point where a battery monitor has become a "must have". I'm going to put that in first and make some other changes and overhauls. I'll then use the monitor to do another assessment of the batteries with a full 20 hour test after a full charge. If there is any question after that, I'll probably replace them as I'd rather do it here than on the road.

If I were just going to continue knocking around the Maine coast, I'd probably just go another year before doing anything. I'm pretty confident about sailing back from anywhere in Maine with a dead engine to where I could pick up a couple of batteries. I don't want to be doing that down in the Bay of Fundy or making landfall somewhere in Nova Scotia for the first time under sail alone.

 

[Stu Jackson]

All this has raised my consciousness to the point where a battery monitor has become a "must have". I'm going to put that in first and make some other changes and overhauls.

Roger, for whatever reasons, that is a great decision.

Guys & gals, that's what we've been trying to explain for the last five or so years.

As I've pointed out a number of times, it was the last thing I did and it should have been the FIRST thing I did for my electrical system.

Can't say we didn't warn ya....

 

[Maddog]

Thanks Stu, That cleared it up. For the price of that BS 5248 model. One of the simpler Battery Monitors would be the way to go.