Alternator does not Fully Charge the Batteries

[tuomas]

Well, after having second look...the 14.2 volts seems to refer to the regulator nominal output...too early conclusions.. surely the alternator can produce higher voltages..?

[hellosailor]

"I tried to find the voltage drop of 702 in the internet but did not find it."
You would need to calculate it, not find it. Assuming your alternator is putting out the maximum rated 60A of power, and your charging lead is a ten foot run of 10AWG wire, the voltage drop (calculated or measured) in ten feet of 10AWG cable carryiung 60A of current is actually worse. According to Voltage Drop Calculator Genuinedealz.com the voltage drop is more than 1.2 volts !

The "isolator" will be using some type of diode, and depending on the type, the inherent voltage drop in power diodes is typically between 0.3 and 0.6 volts. Add that to the 1.2 volt loss in your cable, and your alternator will be losing perhaps 1.8 volts before the power gets to the battery.

If the sense wire is hooked up properly, the alternator will try to compensate by putting out 15-17 volts, but typically they cannot go above ~15 volts and if they do, they'll quickly overheat and then reduce power output anyhow. Catch-22.

So it is entirely possible that the alternator is perfectly good, and it is simply the installation and load killing the charging. At lower loads, there would be less power loss in the alternator output cable, so eventually the battery will charge more--but slowly.

Replacing the alternator output cable with #2 AWG cable, with proper lugs on it, would help regardless of whatever other issues you address. #4 cable at a minimum. (You can use the online calculators to see how each cable size affects voltage loss.)

[westwinds]

Originally Posted by tuomas

Well, after having second look...the 14.2 volts seems to refer to the regulator nominal output...too early conclusions.. surely the alternator can produce higher voltages..?

An alternator can putout considerably higher voltages, there are even ways to make 120 volts; CR4 - Thread: Can a car alternator generate 110v? however, all you want is less than a volt extra. Unfortunately to get that, you would have to set your alternator up to use an external regulator that has a wire on it that can go to the battery that is being charged using one of those manual switches I mentioned earlier that uses a switched field for alternator protection. There was also that relay option. What kind of alternator do you have because I am wondering if it is possible to set it up with an external regulator. Some of those are very expensive, $350 to $450, because they have memory or other methods that are used to program how much current to force into the battery for the maximum charge rate. Examples are Balmer, and Ample Power. Also Powerline, Aqualine, Cruzpro, but I don't know the pricing for those. Then there are other regulators that are only about $50 that are set at 14.4 volts like an automobile. I think GM1960-1985 and Ford 1960-1985 use external regulators. These are not setup as marine alternators so not sure how they would do. You could not use these alternators on an inboard gasoline engine in a boat because of the explosion problem, ignition of gasoline vapor from sparks on the field brushes.

[westwinds]

Another option is leave your alternator setup as it is and use a solar panel to top off the batteries. That way you can also leave the boat for extended periods of time and not have a sulfation problem, or even do a long trip although I would also have the 29 pound, very quiet, EU1000i Honda generator for charging. If you are at a dock, you could also consider a marine battery charger to top everything off.

[btrayfors]

Temporary fix:

1. Get rid of the battery isolator. Install a combiner or, better, an EchoCharge or DuoCharge to keep the start battery topped off. This will avoid the 0.6V drop.

2. Wire the alternator output directly to the house batteries, using sufficiently large cable. Use much larger than you have. Choose the wire size depending on the length of the run and expected maximum amperage.

3. Install an appropriate ANL or MRBF fuse in this new cable, located close to the batteries.

These changes will cost less than $200, depending where you are and how long the run is.

Replace your small charging wire from the alternator to the batteries with much larger cable.

The goal of these changes is to get the maximum voltage from the alternator (14.2V) to the batteries. While 14.2V is still a bit low, it is enough to charge your batteries pretty well.

And, the addition of a solar panel to top off the batteries is a good idea. Wire this directly to the house batteries, and let the combiner or EchoCharge take care of the start battery.

Later, when time/funds permit, convert your alternator to external regulation and install a good regulator (e.g., the Balmar MC-612 or MC-614).

Bill

[tuomas]

Now, after some thinking, let me be more specific:

Volvo states that the engine is delivered with extra sensor disabled, i.e. the the sense wire is shortcut to B +. Therefore, the regulator must have been designed so that it is safe for the batteries were the sense wire in B+ or in the battery terminal. So, the max output is restricted to 14.4 volts + something, together most likely much less than 15 volts.

Now the important part: Correct if I am wrong but in my understanding there is absolutely no way for the regulator to know whether the sense wire is measuring B+ or battery terminal. No dip switches etc to change the max output. Therefore, if considerable voltage drops (like the 1.2 volts mentioned!) are present, and the max output of the regulator is restricted to, say, 14.7 volts, the sense wire does not help since the regulator gets saturated.

Or what do you think?

[mitiempo]

Originally Posted by tuomas

Now, after some thinking, let me be more specific:

Volvo states that the engine is delivered with extra sensor disabled, i.e. the the sense wire is shortcut to B +. Therefore, the regulator must have been designed so that it is safe for the batteries were the sense wire in B+ or in the battery terminal. So, the max output is restricted to 14.4 volts + something, together most likely much less than 15 volts.

Now the important part: Correct if I am wrong but in my understanding there is absolutely no way for the regulator to know whether the sense wire is measuring B+ or battery terminal. No dip switches etc to change the max output. Therefore, if considerable voltage drops (like the 1.2 volts mentioned!) are present, and the max output of the regulator is restricted to, say, 14.7 volts, the sense wire does not help since the regulator gets saturated.

Or what do you think?

That is correct, the alt has no clue where the sense wire is reading the voltage from.

I agree with Bill, lose the battery isolator, upgrade the wire to larger, and add an Echo Charge or similar.

[hellosailor]

tuomas, what you apparently have is a conventional "3-wire" alternator, which has been set up as a "1-wire" system. Builders do this because there is no simple (cheap) way to move the sense wire between different battery banks, so if you have more than one battery, the superior 3-wire system costs more to install. Instead, they cripple it by attaching the sense wire directly to the output, effectively programming the alternator regulator to one fixed voltage which makes no accommodation for battery condition. The justification for this is that it is "good enough" it is "cheap" and the average boater won't ever know that replacing his batteries every 3-4 years isn't normal.

Taking the sense lead directly to the batterybank, assuming there is only ONE battery bank, works much better. If there are two batteries (i.e. house and starter) then either you need to accommodate switching the sense lead when you switch batteries manually, or, you leave the sense lead on one battery, and charge the other via an Echocharge or other charge combiner, so that the sense lead will always see the "combined" voltage level and accommodate for that.

[donradcliffe]

The way a voltage regulator works is that it compares the voltage on its sense wire to some setpoint, say 14.1v. If the sensed voltage is less than the setpoint, it raises the voltage on the field wire, and if it is more, it lowers the voltage on the field wire. The voltage on the field wire (typically 2-12v) pushes current through the brushes into the spinning field coil in the alternator. The spinning rotor coil creates a varying magnetic field in the stator coils, and makes alternating current flow through the (3) stators. The alternating current is then rectified to DC by the diodes, and output through the B+ post.

The alternator has no clue what is going on, except for the field voltage it gets from the regulator. If you have an externally regulated alternator and can gain access to the field, its possible to test the alternator by flashing the field wire to the B+ post;bypassing the regulator and putting the maximum 12v on the field. Internally regulated alternators are harder to diagnose because the F wire is not usually accessible, but it possible to convert any alternator to external regulation.

Its not clear yet whether the OP's alternator regulator is in external sense mode or not. If the sense wire has been removed from the B+ and routed to the positive battery post on the HOUSE bank, it should be wired correctly. In that case the regulator should be controlling the field voltage to make the voltage AT THE BATTERY equal to the setpoint, say 14.1v. The measured alternator output voltage at the B+ should be 14.1v plus the isolator drop plus the wiring drop, or maybe 15 volts. The alternator is capable of operating at well over 15 volts (it is limited by the reverse voltage specs on its stator diodes, which is why you never want to run an alternator without hooking the output to a battery).

I'd get my trusty clamp-on ammeter
Sears.com
and run some tests.

1. Start the engine and (using the SAME instrument) measure the voltage between the B+ and ground and then the house battery positive terminal and the same ground, then the starter battery and ground. Also clamp the ammeter around the wire from the B+ and the isolator and measure the output current, then around the wires from the isolator to each battery and measure that current. Finally, measure the voltage between the ground you have used and the battery negative posts, then the ground to the alternator case.

2. If the alternator output is less than 20 amps, turn on all the electrical equipment you can and repeat test 1.

3. If the results of the first two tests look reasonable, lift the sense wire off the battery terminal--the alternator output should go to max and all voltages should rise. BTW, if you have an externally sensed regulator and you are getting excessive voltages, a broken sense wire should be the first place you look.

In any case, I'd probably replace the wiring with 4 awg (25mm2).

[westwinds]

Originally Posted by hellosailor

...Assuming your alternator is putting out the maximum rated 60A of power, and your charging lead is a ten foot run of 10AWG wire, the voltage drop (calculated or measured) in ten feet of 10AWG cable carryiung 60A of current is actually worse. According to Voltage Drop Calculator Genuinedealz.com the voltage drop is more than 1.2 volts...)

I tried the Genuinedealz calculator and got the same answer you did, but then I tried American wire gauge - Wikipedia, the free encyclopedia and see that 10 gauge wire has 0.9989 ohms per 1000 feet. That would be 0.009989 ohms for 10 feet. If we use ohms law and multiply 0.009989 ohms by 60 amps we get a voltage drop of 0.60 volts. Maybe the voltage drop was doubled because the thought is that there is a return 10 gauge wire for ground? If we use the return ground thinking, then for a 0.3 volt drop, the gauge would be 7. A 0.3 volt drop is the usually accepted amount for calculating voltage drop from battery to a device that needs power. If we want say a 0.15 volt drop, then lets use 4 gauge wire.

[westwinds]

And here is probably the cheapest method. Run the B+ and field sense wire to the positive post of the engine battery, then use a switch like this : Hella Marine on Off Battery Master Disconnect Switch 002843011 | eBay
to connect the house battery to the engine battery using 4 gauge wire. Get rid of the 702 splitter. When the engine is running, have the disconnect switch turned on to charge both batteries. Turn the switch off while taking electricity from the house battery while at anchor to preserve the power in the engine battery for starting. If something goes wrong with the engine battery like a dead cell, you can always turn on the disconnect switch to start the engine on the house battery.

[mitiempo]

I would not use a wire sized for alternator output based on 3% voltage drop. I would use the chart or calculator to find the gauge for 3% voltage drop and then increase it a size or 2. This is not a place for any appreciable drop.

14.4 volts with a 3% voltage drop is 13.96 volts.

And yes, the distance is there and back.

[westwinds]

A 4 gauge battery cable of ten feet gives 0.15 volt drop which is about a 1% drop. A battery cable is already made up and manufactured in quantity so should be the easiest and cheapest way to go. Besides, if starter current could be carried from the house battery in the case where the engine battery was discharged or defective, this is what should be specified.

[westwinds]

Originally Posted by tuomas

Now, after some thinking, let me be more specific:

Volvo states that the engine is delivered with extra sensor disabled, i.e. the the sense wire is shortcut to B +. Therefore, the regulator must have been designed so that it is safe for the batteries were the sense wire in B+ or in the battery terminal. So, the max output is restricted to 14.4 volts + something, together most likely much less than 15 volts.

Tuomas,

How long is the wire from the alternator to the engine battery and from the engine battery to the house battery?

[mitiempo]

For finding voltage drop in DC wiring you have to use the length of the positive AND the return negative. 4 awg does give you a 3% drop as I posted, but that takes 14.4 down to 13.96 volts - really unacceptable. 2 awg results in a 2% drop in voltage and is still only 14.11 volts at the end of a 10' run - 20' there and back. I would go heavier still as it makes no sense to save a few dollars and end up with a battery bank that takes too long to charge. On a powerboat with long engine run times it is less of an issue, but on a sailboat where one wants engine run time as short as possible it is a lot more important.

Here is the wire calc I use most often: AWG by wire length/amps calculator

I got this link from Mainesail a few years ago.