Balmar Regulator Sensing lead placement

[ontherocks83]

Over this winter I am redoing a good portion of my electrical system. I have been extensively reading Mainesails' webpage and I am essentially copying his diagram below, and am going to be ordering a Balmar alt and regulator along with a bunch other stuff from MHT over the winter. Anyways as I was reading his article about voltage sensing I realized when I go to wire the MC-614 voltage sensing lead I'm not quite sure where to put it.

I know it should go on the house positive post, but if the House bank ever has a catastrophic failure and needs to be isolated, then the alt is going to be sensing a bad bank while charging the start battery through the charging bus bar. I was thinking of then putting it on the bus side of the house isolation switch but am worried there would be too much drop through the switch and wires.

What is the best place to put the voltage sensing lead from the voltage regulator?

Do I?
A: leave it on the House Positve terminal (like it's supposed to be) and not worry about the off chance the bank will have a catastrophic failure
B: Put it on the bus side of the emergency disconnect switch, that way it can sense the start battery when in "emergency mode"
C: something else?

 

[Rich Stidger]

I put it on the positive battery terminal. Don't forget the ground reference on the negative terminal too.

 

[dlochner]

In order to have the regulator efficiently charge the battery, it must have the most accurate voltage sense possible. That means sensing the voltage at the battery post, both the positive and negative.

 

[jssailem]

If like most of us, you are going to be charging the House bank primarily and letting the ARC charge the Starter battery. Should your House Bank fail, you‘ll use the starter battery to start the engine and get you to port where you‘ll resolve the House battery problem.

If it takes you more than a 24 hour period to resolve your house battery issue and you become concerned, you can always move the battery sensor from the House to the Starter battery for a temporary period.

 

[ontherocks83]

If it takes you more than a 24 hour period to resolve your house battery issue and you become concerned, you can always move the battery sensor from the House to the Starter battery for a temporary period.

I guess that is a big part of my question; How long can you run it on the start battery with it sensing a bad bank before you start to do serious damage to the start battery? I get it's only a C30 and I'm not crossing oceans, but my house bank is only 2 6v batteries, its not like I have 4 of them and if one fails I can take 2 out of the circuit to make a smaller house bank. I'm sure I'm over thinking this / over worried about nothing, but when going through this much effort and money I just want to make sure I'm doing things correctly and the best way possible.

 

[dlochner]

I guess that is a big part of my question; How long can you run it on the start battery with it sensing a bad bank before you start to do serious damage to the start battery? I get it's only a C30 and I'm not crossing oceans, but my house bank is only 2 6v batteries, its not like I have 4 of them and if one fails I can take 2 out of the circuit to make a smaller house bank. I'm sure I'm over thinking this / over worried about nothing, but when going through this much effort and money I just want to make sure I'm doing things correctly and the best way possible.

It is fairly rare for a battery from a good brand that is well maintained catastrophically fails. If it does, it will take the other batteries out before you have time fix the problem. That's why an ACR between the house and start batteries is important as well as the ability to isolate the house and start batteries.

How long the start battery can support the electrical systems on the boat really depends on what's turned on. A typical Group 24 start battery has a capacity of about 70 amp hours. That's more than enough to get home from a day sail or longer if unnecessary electrical demands are eliminated. That might mean hand steering, warm beer, and no music.

 

[jssailem]

my house bank is only 2 6v batteries,.....I'm sure I'm over thinking this

No not really. I thought about this. While considering the 2 six volt battery plan and 235 amp hours it seemed like a good idea.
But then I found batteries designed for Sweeper and Aerial lifts. They have 135 amp hours. 700-800 cycles and are 12 volt deep cycle batteries. Dyno Battery - Premium Quality Battery Manufacturing - Made in the USA

These addressed the challenge and did it at a favorable price point.

 

[sailcrazy1]

Following...our standard OEM alternator is just not doing the job, and I want to protect the life of our Trojan T105s. Seriously looking at installing a Balmar external regulated alternator.

 

[dlochner]

Following...our standard OEM alternator is just not doing the job, and I want to protect the life of our Trojan T105s. Seriously looking at installing a Balmar external regulated alternator.

This not surprising. OEM alternators are often wired to protect the alternator and keep the start battery charged. This leads to chronic under charging. To do this right, you'll need to look at the entire DC electric system. A good place to start is @Maine Sail's site, MarineHowTo.com and his alternator offerings also his forum here on SBO, Musings with Maine Sail.

A number of us on the forum have made significant changes to our OEM wired boats based on his website and recommendations.

 

[jssailem]

What @dlochner said.

 

[dLj]

A number of us on the forum have made significant changes to our OEM wired boats based on his website and recommendations.

I'll only add - with great success/satisfaction!

dj

 

[Stan Galper]

My Balmar "Smart" regulator charged my batteries too slowly until I connected the sense wire to the positive terminal of a battery. If you connect it anywhere else, the regulator won't compensate for the voltage drop from that point to the battery. That causes the regulator to measure higher than the actual battery voltage, so it will charge more slowly than it should. My sense wire is a #8 AWG, somewhat heavy to eliminate any potential voltage drop from the battery back to the regulator.

 

[dlochner]

My Balmar "Smart" regulator charged my batteries too slowly until I connected the sense wire to the positive terminal of a battery. If you connect it anywhere else, the regulator won't compensate for the voltage drop from that point to the battery. That causes the regulator to measure higher than the actual battery voltage, so it will charge more slowly than it should. My sense wire is a #8 AWG, somewhat heavy to eliminate any potential voltage drop from the battery back to the regulator.

That's correct. However, #8 AWG is way more wire than you need, since the actual current being used to measure the voltage is very low. 12 or 14 gauge will be more than adequate. Don't have manual handy so I may be off a little, the Balmar Smartguage only recommends 14 ga for its sense wires.

 

[LeslieTroyer]

I’m going to be the contrarian here (love doing that) and say if your worried about a couple hundredths of a volt difference between a buss and the terminal. 1) go up two sizes in the cable 2) jack up the various phase voltages to correspond to the measured drop at the end of the phase. I’m sure you’ll be 1000% better that has no battery reference.

BTW my 614 reference is on the battery fuse. So I just need to replace the MBRF fuse with a dead one, if your using ANL put the reference on the house side I’d the fuse and pull the fuse if your house dies.

 

[dlochner]

I’m going to be the contrarian here (love doing that) and say if your worried about a couple hundredths of a volt difference between a buss and the terminal. 1) go up two sizes in the cable 2) jack up the various phase voltages to correspond to the measured drop at the end of the phase. I’m sure you’ll be 1000% better that has no battery reference.

BTW my 614 reference is on the battery fuse. So I just need to replace the MBRF fuse with a dead one, if your using ANL put the reference on the house side I’d the fuse and pull the fuse if your house dies.

Way easier and cheaper to just attach the sense wire to the battery and use a wire a size or two bigger, which would be 14 ga.

 

[Maine Sail]

Over this winter I am redoing a good portion of my electrical system. I have been extensively reading Mainesails' webpage and I am essentially copying his diagram below, and am going to be ordering a Balmar alt and regulator along with a bunch other stuff from MHT over the winter. Anyways as I was reading his article about voltage sensing I realized when I go to wire the MC-614 voltage sensing lead I'm not quite sure where to put it.

I know it should go on the house positive post, but if the House bank ever has a catastrophic failure and needs to be isolated, then the alt is going to be sensing a bad bank while charging the start battery through the charging bus bar. I was thinking of then putting it on the bus side of the house isolation switch but am worried there would be too much drop through the switch and wires.

What is the best place to put the voltage sensing lead from the voltage regulator?

Do I?
A: leave it on the House Positve terminal (like it's supposed to be) and not worry about the off chance the bank will have a catastrophic failure
B: Put it on the bus side of the emergency disconnect switch, that way it can sense the start battery when in "emergency mode"
C: something else?

Keep in mind that this drawing has the emergency ON/OFF isolation switch inches from the battery inside the battery compartment. Also keep in mind that the drawing is designed to allow charging to remain with the active bank. If v-sense goes to house and the isolation switch is turned off you will fry the starter bank!

Rx:
#1 Neg v-sense can still go to house negative, no impact there

#2 The Blue Sea manual battery switches are rated for;
m-Series = 300A continuous,
e-Series = 350A continuous
HD-Series at 600A continuous

Voltage drop across one, at typical charging voltages, is quite low.

#3 If concerned beef up the cable between the switch & battery and busbar and switch to 4/0.

The point is to get as close to the battery as is possible and still yield good charging performance. The benefits of charging staying with the active bank, and not running a risk of runaway voltage, tends to outweigh the minimal drop of routing positive v-sense to the busbar or to the charge side stud of the battery switch. Compared to most charging systems you will be well ahead of the game just because you have a v-sense circuit.

 

[Maine Sail]

That's correct. However, #8 AWG is way more wire than you need, since the actual current being used to measure the voltage is very low. 12 or 14 gauge will be more than adequate. Don't have manual handy so I may be off a little, the Balmar Smartguage only recommends 14 ga for its sense wires.

The red v-sense wire on an MC-614 carries no current at all, it is just a sensing circuit. On the ARS-5 the red power wire in the harness is also v-sense so if it is a long run to the bank this wire can carry as much as 3-7A or so and will need to be bumped up accordingly. This is why the MC-614 is the better value of the two.