Running starter through a shunt.

[RickB]

The OP wrote "I want to be able to measure the total usage of the battery bank. " and went on to ask if there would be any problems.

So why does everyone have to try so hard to convince him to do something else? It is none of our business why he wants to do something or if it is even practical or has any use other than personal amusement. Why do any of us have a boat? Probably very few of us need one for transportation or safety and owning one isn't necessarily the best idea in the world. How would you feel if people starting posting here about what a bad idea it is to have a boat?

Why not just answer the question and if you can't or don't know what the question means then keep out of it?

And why is a shunt any more likely to become a fuse than any other part of the circuit? Geez, the wiring inside a starter or alternator is microscopic compared to the battery cables or a shunt, how come that doesn't upset anyone?

Either help the guy with his project or not, it is HIS project and HIS choice to do it, he didn't ask what you thought about the idea, just if it can be done and if the shunt would present a problem.

 

[FF]

and if the shunt would present a problem.

YES, it poses a danger.

 

[Stray-Cat]

Either help the guy with his project or not, it is HIS project and HIS choice to do it, he didn't ask what you thought about the idea, just if it can be done and if the shunt would present a problem.

It always happens when people feel there is a better way they state their opinion
This is good, its how forums work
Even a manufacturers tech support person may question the op's desires and give alternate ways
This may give the OP pause for thought , but as you say Rick its his decision in the end
Hopefully he will come to a informed conclusion based on the information here
He just has to filter out all the bickering comments in this thread

 

[FF]

This is good, its how forums work

Thread expansion is probably the most useful part of most responses as frequently the OP has no idea what he is actually asking .

Folks that have a desire sometimes need help in defining their Desirements.

 

[RickB]

... frequently the OP has no idea what he is actually asking .

It seems a bit arrogant to assume that when someone asks what time it is he really wants to know what readers think is the best watch is for themselves.

It is noon somewhere, why do you ask?

 

[RickB]

... YES, it poses a danger.

Really, what danger is that? Has there been a rash of shunt induced boat fires recently?

 

[meridian]

ask a simple question!

 

[Stray-Cat]

ask a simple question!

You should know better

 

[Forkliftt]

Ford Lehman manual for the 120 specifies locked rotor draw of 1070 A, running draw of 650 A.

I stand corrected. And informed!

 

[Forkliftt]

As long as you account for the increased resistance of the cable as it heats up from being overloaded.

True. Or the increased resistance of a cold engine.

 

[RickB]

I guess guys can stop "tooling for a number out there that doesn't exist" now.

 

[Moonstruck]

True. Or the increased resistance of a cold engine.

All of that was in Stray-Cats formula. Didn't you see it?

 

[FF]

"Really, what danger is that? Has there been a rash of shunt induced boat fires "recently?

The danger is when the Start button is pushed , there is not even the sound of a click.

A "Much Ungood" way to start the day.

 

[RickB]

The danger is when the Start button is pushed , there is not even the sound of a click.

Would you be so kind as to explain the sequence of events that would lead to such an event?

Has there been a rash of shunt failures lately that have caused loss of DC power on boats?

It makes for a nice throwaway line FF but unless you can back it up with some examples and tell where the failure would occur and for what reason I think you are just blowing smoke ... and none of that smoke is from overheated electrics.

If you are afraid of shunts and can't sleep at night maybe a Hall effect sensor would take some of the fear out of your boating experience and still deliver the information you want.

 

[FF]

A shunt in a start circuit such a poor practice that an example of starter shunt failure is hard to show.

A shunt in the house side is very desired IF one widhes to monitor the SOC.

Asking for a shunt starter failure is on par with asking for examples of 60 ft boats blown ashore because their 1/4 inch anchor line failed.

1/4 inch tie up is very common on moorings when the boat is being "sold" to the insurance co, but sort of rare otherwise.

 

[RickB]

The sky is not falling and placing a shunt in the starting circuit is not "bad practice."
There are thousands of high current DC shunts installed in motor and other power circuits onboard ships where the current flow far exceeds a tiny engine starter.

What is it about a shunt that freaks you out so much? Why is it so much more dangerous than a cable terminal or - gasp - a battery terminal?

This is the kind of myth and "sea story" nonsense that make small boat mechanics and electricians rich ... people read utter nonsense on boating forums and actually believe it even though the people who post the garbage can't support their position with anything more than rumors and their "net creds."

I challenge you to show us why a shunt installed correctly with clean terminals that are properly tightened is any more likely than any other electrical component to fail and cause the sky to fall.

http://www.megacon.com/admin/uploads/Datasheet/Crompton.Shunts.pdf

 

[FF]

I challenge you to show us why a shunt installed correctly with clean terminals that are properly tightened is any more likely than any other electrical component to fail and cause the sky to fall.

A shunt installed "correctly" would have to be large enough to take the LRC of the staterr motor.

This can be 2x to 7x the running current of the starter.

With a say , 1000A or 2000A shunt , what purpose would the setup serve , its accuracy at the minor DC loads of lighting or a bilge or water pump would be outside the accuracy percentage of most SOC monitoring systems.

So as already asked , why bother to monitor the starter for 5 seconds , when the 24/7 ships use of charge and discharge is probably the desirement?

 

[RickB]

Keep trying FF, maybe some day you will find a reason to believe your own myths.

"why bother to monitor the starter for 5 seconds?"

Because it is his boat and his desire to do so ... your boat and your desires don't count. Just because you wouldn't do something doesn't mean you have to create some fantasy about why someone else should not do it.

 

[sunchaser]

Meridian

I recently had a well known yard install a new Magnum 2800 inverter charger and two battery monitor kits (BMK) on our vessel. One could assume these BMKs use shunts. One BMK was for the house batteries and the other for the main engines. The purpose of the BMK for the house batteries is hopefully obvious to those reading this thread. The engine start BMK was installed to insure that I know the operating and at rest health of the 2 8D engine batteries and related charging systems.

This entire system is nicely monitored by Magnum's ER mounted modem and helm location remote. I chose Magnum because they are like my boat, located in the PNW. Had I been on the East Coast, I may have considered Victron.

These 21st century operating and monitoring systems are well worth the cost for the type of remote cruising we do. If you care to, I'd suggest you talk with the suppliers and recognized marine electricians for any shunt related fears and phobias related to this thread.

In my industrial experience shunts are everywhere, with the most interesting on a 0 to 18 RPM electric motors (you read that right, 18).