Voltmeter installation

[fitz73222]

Hey Bob, you got your ears on?

Haven't said that in a long time!

I'm replacing my volt meter on the AS. It has the original 70's chrome metal cased voltmeter that still works except it seems to be very sensitive to any current draw and shows voltage below the actual voltage in the system which I verified. Right now it is wired through the main battery selector switch so when I turn on the switch it shows the voltage in one or both batteries depending on the selection. The PO had house current fed through a large ballast resistor (the size of a automotive ignition coil) to presumably isolate engine noise from the electronics; Its still hooked up. I don't know if it works or not or whether it's relevant.  The problem is; as long as the battery selector switch is turned on, engines off, the voltmeter has a parasitic draw on the batteries. I want to convert it to engine key switch activation but with twin engines. I want to connect both purple wires from the key switches to the + side of the voltmeter. Purple, for Mercs is key switch activated 12 volts for tach, temp, hourmeter, etc for any engine specific duty. My Flowscan captures my engine hours for each engine, which is key switch activated as usual,engine specific and I can select port or starboard engine rpm's, fuel flow, hours, synch or no synch etc.,. Since both purple wires would be tied together at the voltmeter; is there any concern for a 12 volt backfeed  from the active engine to the inactive engine? I'm surmising that if I'm running one engine and the other engine is switched off, there would be no feed going to the "off engine" right? Or would it fool the Flowscan into thinking that that engine was running and collecting unearned hours? Would the off engine tach and temp gauge be fed 12 volts since all grounds are common? Would some sort of blocking diode / isolator (sorry for the 70's electronics dialog) in the purple leads, keep them isolated from one another if I'm running one engine? Should I stop drinking on my afternoon off and hook the f$$^%$ing thing up as it is and live with it?

Your vision is as always, much appreciated!

Farley

[wingtime]

The ballast resistor is interesting.  I would think it does little as a filter....   more than likely it is lowering your house voltage.  I'd check voltage drop across the resistor with a volt meter.

[seabob4]

Farley,
Remember that a voltmeter is simply a way to determine voltage in any circuit, be it a main, branch, whatever.  There is an extremely small amount of amperage used to run the gauge itself (has to be small, or else what would be the use!), but, other than that, the meter simply does it's job...

That being said, with twins, one might say that putting the batt switches on 1 and 2 (effectively isolating the batts) should give one an accurate reading for each engines system voltage.  But wait, we have the common ground...how does this affect each engine's voltage, or the house for that matter?  So this is what I would do.  Install 2 voltmeters, each powered from it's respective purple (ign hot) and ground wires coming off it's respective engine harness (port and starboard).  Turn the motors off, no amp draw.  Sit back, have a couple cold ones, call it a well done day.

IMO too many people try to read to much into what they have, try to make things too complicated, want to keep an eye on every single little millivolt that is escaping...all at the cost of being able to relax out on the water.  We here in FL can usually count on batts starting to go south at around 3 years, we're lucky if we get 5 years out of them.  Heat kills.  Sooo....carry a spare on board, a small package of 50 lbs or so that can be stowed easily and be put to use when necessary.  Another aspect about batts is that you never know when a GOOD one, even one a single year old may crap out due to a bad cell.  They don't make chit like they used to, even Optima's, East Penn, whomever...

In short, don't make a mountain out of a mole hill...

[fitz73222]

Farley,
Remember that a voltmeter is simply a way to determine voltage in any circuit, be it a main, branch, whatever.  There is an extremely small amount of amperage used to run the gauge itself (has to be small, or else what would be the use!), but, other than that, the meter simply does it's job...

That being said, with twins, one might say that putting the batt switches on 1 and 2 (effectively isolating the batts) should give one an accurate reading for each engines system voltage.  But wait, we have the common ground...how does this affect each engine's voltage, or the house for that matter?  So this is what I would do.  Install 2 voltmeters, each powered from it's respective purple (ign hot) and ground wires coming off it's respective engine harness (port and starboard).  Turn the motors off, no amp draw.  Sit back, have a couple cold ones, call it a well done day.

IMO too many people try to read to much into what they have, try to make things too complicated, want to keep an eye on every single little millivolt that is escaping...all at the cost of being able to relax out on the water.  We here in FL can usually count on batts starting to go south at around 3 years, we're lucky if we get 5 years out of them.  Heat kills.  Sooo....carry a spare on board, a small package of 50 lbs or so that can be stowed easily and be put to use when necessary.  Another aspect about batts is that you never know when a GOOD one, even one a single year old may crap out due to a bad cell.  They don't make chit like they used to, even Optima's, East Penn, whomever...



In short, don't make a mountain out of a mole hill...

The golden rule...KISS! Thanks for reeling me in...

[John Jones]

In short, don't make a mountain out of a mole hill...

Very well thought out and well put SB.
 

[GoneFission]

Old volt meters do have some parasitic loss, but newer ones have very little.  Look at the specs for the meter and you can see what the loss is from the resistance value of the meter - often 20K to 40K ohms per volt.  So a decent meter reading 12 volts has a resistance of say 220K Ohms - that's a very low draw on the battery.  

Rather than two meters, how about a SPDT switch so you can just go back an forth from one battery to the other on the same meter?  Also, if you get a switch with a "center off" - there will be no battery loss from the meter!  

http://www.grainger.com/Grainger/CARLIN ... vc=IDPBBZ2

http://www.adamsonindustries.com/replac ... enter-off/

[fitz73222]

Old volt meters do have some parasitic loss, but newer ones have very little.  Look at the specs for the meter and you can see what the loss is from the resistance value of the meter - often 20K to 40K ohms per volt.  So a decent meter reading 12 volts has a resistance of say 220K Ohms - that's a very low draw on the battery.  

Rather than two meters, how about a SPDT switch so you can just go back an forth from one battery to the other on the same meter?  Also, if you get a switch with a "center off" - there will be no battery loss from the meter!  

http://www.grainger.com/Grainger/CARLIN ... vc=IDPBBZ2

http://www.adamsonindustries.com/replac ... enter-off/

Thanks John,,

I had come to the same conclusion so I'm glad you concur. Seabob is right, I should relax. My girlfriend criticizes me when we go out in the boats that I pay to much attention to systems and gaze at the engines ( they are pretty aren't they?) and not enough attention to her! I must have been a flight engineer in a previous life. I don't want to fly the damn plane; I just want to look at the gauges! Strange how our brains work...

[seabob4]

Good idea John.  Saves space, cost, etc., is done quite often with fuel gauges as well when 2 tanks are involved...

Farley, when I go to boat shows, I don't look at the shiny glass or the shiny hardware (I DO look at the shiny females!!).  I stick my head into engine rooms, bilges, places builders would rather us not see.

I've seen enough pretty boats in my lifetime!

[gran398]

My girlfriend criticizes me when we go out in the boats that I pay to much attention to systems and gaze at the engines ( they are pretty aren't they?) and not enough attention to her!





Off-topic:

Farl, this is also true in marriage, but 10X.

Remember the phrase "That damn Aquanet"

If the adjective "damn" is replaced with an adjective that begins with "f"....its time for reevaluation

[GoneFission]

Remember the phrase "That damn Aquanet"

If the adjective "damn" is replaced with an adjective that begins with "f"....its time for reevaluation

I don't understand the problem with the Aquanet!  

[gran398]

Me either.

And it is offered in inviting and attractive packaging.

 

[Capt. Bob]

While it's not retro or in the style of most analog gauge equipped boats, a digital readout gives an accurate description and draws very low power. For those with the Yamaha powered rigs with the old digital gauges, it works (and somewhat looks) quite well. I installed a Datel model (I run the same model on my motorcycle). It's interesting to see just what's going on with the battery at any given time and for old eyes, it's easy to see at a distance.

Just another  

[dburr]

Amazon has hydrometers for less then $10.. One of these showed me that my $OMG tractor battery was getting sick even though it showed 11.9vdc at rest and charged to 13.9 when running.  Only drawback is you have to have old school lead acid "open" cell batteries to take advantage of it

[RickK]

What is the gauge to the right CB

[Capt. Bob]

What is the gauge to the right CB

It's a % charge indicator. I had an analog one on my CCP which was a quick indicator of when to hook up the at home charger. I added the one in the photo to fill the same need in the WAC and to replace the dead hour meter that resided in that spot.

In that photo, the volt meter is indicating 12.48 volts but the % charge shows the level of charge at 70% +/-. I usually throw the charger on the battery when it gets around 50%. The one upside of gel batteries is that they can draw down (sit idle in the back yard) to low levels and then be recharged with limited damage.

I have kicked around a water temp gauge to replace it but I need a new tachometer first. It's the gauge (tach) along with the volt meter that I rely on for the most part.