Link 20 Voltage Readings

[Stu Jackson]

Craig,

Without getting into more detail now, which I can do later, it appears that your setup allows for combining the two banks, but NOT having only the reserve bank supply power to the DP.  Therefore, your concerns about running anything during equalization are correct.  Don't try it.

[Craig Illman]

Stu - The objective of the bank combination switch was to provide an alternate start source. I didn't contemplate the reverse.

Craig

[Stu Jackson]

I understand, but based on my (exhaustive?) discussion of the demerits of the new dual circuit switch (Replies 18 and 20: http://c34.org/bbs/index.php/topic,4623.15.html), I recommend that you reconsider your setup to permit either of the two banks to provide power to the starter, rather than only the reserve or the combined banks.  The basic idea is if you need the house bank with a dead reserve bank, the last thing you'd wanna do is to combine them.  Same reasoning worked when I discussed the dual circuit switch.  Just more of my zany electrical ranting...

[Craig Illman]

Terry & Stu - Xantrex came back and wanted me to check the voltage on pins 1 and 4 of the Link. They also said there wasn't any adjustment. I expect the tiny gauge wiring from the Link to the battery box could account for the .2V variance. I hope adding a more robust ground path from the charger to the battery box reduces the variance I see on the charger display.

Craig

[Craig Illman]

Stu - I agree, but it's easy to disconnect the start battery by tripping the breaker. Compromises........

Craig

[Stu Jackson]

Craig, maybe I wasn't clear, just the other way around.  How do you disconnect the house bank and have the reserve bank serve the DP?

Re: voltage and Maine Sail's point, the specs on the units themselves say good to +/- XYZ volts, which i believe is either an eight to a quarter volt anyway.  Don't sweat the voltage diffs.

[Craig Illman]

Stu - other than maybe listening to the radio while equalizing, I can't think of a lot of reasons to use the start battery to run the house loads. If I can get the engine running, then I have an alternator to provide 12v to the house loads. It's pretty easy to split my house bank if one of the four T-105s fails.

I'll try and not get too concerned about voltage variances. MaineSail's meters showed a .07V variance, but I was getting a .5V variance between the Link 20 and the Xantrex XC3012. I'll report back if that variance is reduced after running the upgraded ground leg from the panel area to the battery box.

[Roland Gendreau]

I have a Link 2000 on Gratitude and noticed a 0.7v difference between voltage measured at the battery terminal on the house bank and the voltage read on the Link display.

To determine where the issue was, I swapped the battery voltage measurement leads on the house and starting batteries, and  the 0.7 voltage difference then moved to the starting battery. I also checked the voltage at the terminal block close to the Link and measured the same voltage difference there as at the battery, not as displayed on the panel. So this indicated to the problem is internal to the Link.

I then called Tekris Power Electronics (732 938 4996) who provides service on the Link units and they indicated they can recalibrate the Link 2000 to correct the issue. I don't know whether the Link 10 can be similarly recalibrated.  I don't recall the price they quoted me; it wasnt cheap but the 0.7v difference is more than I want to live with.

I plan to pull the Link panel and ship it to them in the near future.

[Link service ref - for searching - Stu 4/14/10]
Roland Gendreau
Gratitude #1183

[Stu Jackson]

Roland, why not consider saving some hard earned $$ and use the known 0.7 V like a deviation table for a compass?  Since the purpose of the Link is to tell you how much power you have left in the bank and is not voltage dependent, it could be a costly exercise to "fix."  Your boat, your choice.

Craig, I hear ya, but don't think that's my only reason.  Although four to six hours without music would be "painful."  I guess we're coming from two different electrical system design "theories"

-- dedicated reserve bank used to start engine all the time, house to DP; combine banks if reserve fails to start the engine (if the house bank fails, backup to the DP is available from the reserve bank but only in combined mode, not separately; 'cuz there's no switch in the line that combines the house and reserve banks)  This is like the dual circuit switch battery management approach, which I believe is just plain stupid - why would anyone want to combine a dead bank with a good one?.

---OR----  

--  either bank can be used for either service, combine is available through 1-2-B or other switches but never intended to be used because combining a bad bank with a good one makes no sense to me.

The B on a 1-2-B switch can be used as a Backup for a failed combiner or echo charger, or when charging sources are present, if the charging source goes to directly the house bank (PDP).  It's a great backup, but NOT to be used to combine a dead and good bank.  Use #2 for the reserve and if 1 fails simply switch to 2!

As long as it works for you, and you did a great job documenting it.

[Fuzzy]

Roland:
Could the .7 volt difference be the voltage drop in the leads from your batteries to the Link monitor???

Larry

[Ron Hill]

Roland : Before I spent the money on sending your unit for recalibration, I'd try this first. 
Take out your Link unit and put some short temporary wires on the leads that check the voltage and connect them directly to the battery.  That way you can isolate whether it's the unit or the wiring/connections.  A thought.

[Roland Gendreau]

Ron

I eliminated the leads as the source of the voltage drop by testing 2 things:

1. Since the voltage of the starting battery reads correctly, I used the starting battery leads to measure the voltage of the house battery.  The voltage read correctly at the display.

I then used the leads to the house battery to measure the starting battery - the voltage read 0.7 volts lower at the display.

So the low voltage problem moved with the leads and was isolated to the lead to the house battery.

2. The leads to the batteries originate at a terminal block near the Link.  I measured the battery voltages with a DVM at that terminal block and it reads the same as at the batteries themselves. That eliminates the leads from the termals to the batteries as being the source of the problem.   

The wires from the terminal blocks to the link are fairly short and go to a plug connector I believe.

[Ted Pounds]

Roland,
If I read your post correctly it sounds like the problem is in the leads from the terminal block to the Link for the house battery.  You say there is a plug in the wires.  That's the first place I would look for the problem.  Use the ohm function on your meter to compare the resistance of the two leads.  I suspect you'll find a very slight resistance in the house lead.  You will need a fairly sensitive ohm meter to check this.

[Craig Illman]

Stu, Ron, et. al. - I added the 6ga ground run from the battery box to behind the panel today. It looks like I managed to reduce between .15 & .2V of the .3V variance I had from the charger to the batteries. My only close call was that I got my hand stuck temporarily between the intake hose for the macerator and the hose to the holding tank from the head. I'm not sure I would have been able to reach my cellphone with my other hand to have called 9-1-1. Ah, the joys of running wiring in a boat!

Craig 

[Stu Jackson]

Craig & I had an offline discussion about this:

Craig,

I've been seen reviewing your wiring diagram.  Again, nice job.  I think
most people don't have one, and I can't understand how they run their boats
without them.

I think there's a way to run your house loads with the reserve bank if your
house bank bites the dust (for whatever reason, and we both know it won't,
right? ).

If you pop the house bank 150A breaker (lower right on your diagram), the
reserve bank power will run this way:  reserve bank through #1 and reserve
150 A breaker to bus bar, #2 to reserve bank switch, #2 to house bank 150 A
breaker, #4 original to panel on/off switch, to loads.

You may have figured this out already, but I finally spent some time to play
detective.

If you trip the house 150 A breaker, it looks like you'd disconnect the Link
wiring and maybe dump its historical information, so unless that won't
happen you may be hesitant to give this scenario a test, unless you don't
have or care about the history or you don't have it anyway.

That's a pretty elegant re-use of the #4 originals, "well done, Weldon!"

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Stu - I hadn't thought about that alternative. I might not have the drawing
exactly correct, because I think the breaker on the house bank just goes to
the panel. If I lost the house bank, it would be very easy to disconnect the
bank flip the combine switch. Obviously, I'm not too worried about it. What
the drawing doesn't show is my windlass connected to the "start" battery and
the inverter connected to the house bank. I have a 1-2-both switch going to
the inverter that lets me split the house bank and feed the inverter from
one isolated pair while the other pair feeds the panel. A previous inverter
would shut down when the alternator went into bulk mode trying to replace
the amps, so I setup a switch to split the two sets of T-105s.

My start battery is a group 24 of unknown age that's a sealed PbCa. I'll
probably replace it with an Optima when it won't crank the engine.

I'm glad I did the Visio drawing. In less than a year I was checking it to
see exactly what I'd engineered. My battery box isn't the prettiest, but I'm
not an artist or a perfectionist.

Craig