Start battery dead?

[mariner36bob]

20+ year old 50amp alternator.
House bank: (2) 6 volt trojans.
Start bank: (1) 700CCA lead acid.
Victron 602s monitor.
Blue Seas automatic charging relay. (Closes and Combines at 13.0 volts after 30 seconds. Opens and "un"combines at 12.75volts for 30 Seconds)

Alternator is wired to charge start battery first, then ACR should and does kick in.

So it goes like this... I start the boat, motor out, shut it down and sail. I use the house bank to use electronics etc. then later, re-start to motor back to mooring and to recharge the house bank used.

Worked great for two years....

Alternator puts out 7-8 Amps, start battery voltage rises to 14.4 and after a few minutes the combiner kicks in. Great.

The Amps increase to 12-20 amps, the house bank voltage begins to rise into 13's....still looking good...

Meanwhile the Start battery falls to 12.7-12.8 and combiner kicks off.

This cycles over and over again so I'm not getting start battery voltage high enough to allow combiner to stay closed and charge through to the house bank.

Yesterday I motored for 4-5 hours and never got the combiner to stay open and charge the house.

Eventually i had to cut off the diesel, shut off the start battery, use the house bank to start the diesel and was able to force feed Amps to the house bank, bypassing the start battery. This worked.

So if the start battery is taking 14 volts/7-8 amps and then drops to 12.75, my start battery is junk, right?

Thanks.


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[svlamorocha]

Originally Posted by mariner36bob

So if the start battery is taking 14 volts/7-8 amps and then drops to 12.75, my start battery is junk, right?

No; the 12.75 voltage only tells you that the battery is not being charged.
Most batteries will drop to circa 12.7V (or less if not fully charged) very quickly after you stop charging them.

[svlamorocha]

Originally Posted by mariner36bob

Blue Seas automatic charging relay. (Closes and Combines at 13.0 volts after

Blue Seas makes various models of ACRs (SI, etc) , which are based on different combine algorithms. What model do you have? That will help us think about this.

[leftbrainstuff]

It's always a challenge to root cause on the forum. Lets start with basics.

Is your start battery full of electrolyte?

Have you load tested the start battery? A good battery should read 10.5+V while cranking.

Have you checked for voltage drop in your start battery circuit. Could there be a bad connection you haven't gound yet.

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[S/V Illusion]

Re wire your ACR to allow charging house bank first rather than a single start battery and your problem disappears.

[mariner36bob]

Model SI.


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[svlamorocha]

Originally Posted by mariner36bob

20+ year old 50amp alternator.
House bank: (2) 6 volt trojans.
Start bank: (1) 700CCA lead acid.
Victron 602s monitor.
Blue Seas automatic charging relay. (Closes and Combines at 13.0 volts after 30 seconds. Opens and "un"combines at 12.75volts for 30 Seconds)

Alternator is wired to charge start battery first, then ACR should and does kick in.

So it goes like this... I start the boat, motor out, shut it down and sail. I use the house bank to use electronics etc. then later, re-start to motor back to mooring and to recharge the house bank used.

Worked great for two years....

Alternator puts out 7-8 Amps, start battery voltage rises to 14.4 and after a few minutes the combiner kicks in. Great.

The Amps increase to 12-20 amps, the house bank voltage begins to rise into 13's....still looking good...

Meanwhile the Start battery falls to 12.7-12.8 and combiner kicks off.

This cycles over and over again so I'm not getting start battery voltage high enough to allow combiner to stay closed and charge through to the house bank.

Yesterday I motored for 4-5 hours and never got the combiner to stay open and charge the house.

Eventually i had to cut off the diesel, shut off the start battery, use the house bank to start the diesel and was able to force feed Amps to the house bank, bypassing the start battery. This worked.

So if the start battery is taking 14 volts/7-8 amps and then drops to 12.75, my start battery is junk, right?

Thanks.


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I am afraid I do not follow what part of the description relates to how the thing (does not) work now vs how the thing used to work. Can you please clarify?

In the meantime, here is the troubleshooting chart:

http://assets.bluesea.com/files/resources/technical_briefs/Technical_Brief_7610_FAQ_Matrix.pdf

Other than what is said in the chart, my first step would be to record voltages over time for each bank, both across battery terminals and at the ACR (this means four sets of voltages). That means recording four voltages as mesured by a multimeter connected directly to the relevant set of battery or ACR terminals. Don´t trust the battery monitor because many times they are not installed correctly.

I am suspicious of the voltages you report because if the connections and wire sizing are good both banks should have roughly the same voltage while combined.

[donradcliffe]

Originally Posted by S/V Illusion

Re wire your ACR to allow charging house bank first rather than a single start battery and your problem disappears.

+1000

[skipmac]

I will also add my agreement to S/V Illusion's suggestion.

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[Cheechako]

Other than the above two good posts above ^, charge that battery at the dock and let it sit overnight with the cable off. if it's flat in the am, your battery has a short.

[Maine Sail]

Sounds like you are getting a very typical issue called "relay cycling" due to an incorrectly installed ACR, for the application..

In a house bank / start bank situation, with a small-ish charge source, the alt and all other charge sources should feed the house bank first, not the start battery. Your alt, and especially true if you have solar, simply can't keep up with the demand created by the house bank. When it combines the house bank is sucking the voltage back down to the uncombine point...


This is perhaps the #1 issue I fix when dealing with ACR's. Sadly the instructions are written for smallish equally sized banks, not large heavily depleted house banks and a small start battery.

Wayne Kelsoe of Blue Sea wrote a tech article dealing with relay cycling after many installers, like myself, complained the instructions were inadequate for typical house/start bank setups on cruising boats. The instructions work great if you have a small center console with two group 27's, but not a cruising boat with disproportionately sized banks..........

Blue Sea Tech Article - Preventing Cycling in Battery Combiners (LINK)



.

[Stu Jackson]

A number of years ago, Maine Sail & I were both posting on ybw.com, a UK magazine sponsored boating forum.

For some bizarre reason most UK skippers with large house banks on sailboats still insist on sending their AO to the start or reserve bank and then through a combiner/relay/ACR to their larger house bank. One particular skipper literally violently responded to my suggestion that they send their AO to their house banks and Maine Sail advised me of it.

We both eventually stopped bothering.

The Blue Sea link provided by Maine Sail explains just why we'd been saying that for years. I still don't know why they keep doing it.

Large house bank, small start bank, AO to house bank. NOT start bank.

Equal banks on a motorboat that starts & stops the engine regularly so the start bank IS lower and NEEDS more charge, then AO to start bank is fine.

Just like Blue Sea says.

This is basic electrical system design: you send the charge to where it is needed the most, and for sailboats with larger house banks which get used all night long (lights, music, fridge, etc.), the house bank is where it is needed most in the morning when the engine starts up.

[mariner36bob]

Outstanding. Thank you all.

Quick swap of wires and I'm back in the saddle.

Excellent info as always. Makes perfect sense and works as described. I appreciate the advice as well as the reasoning behind it.

I checked my install twice against the blue seas instructions. I did exactly as written, imagine that.

I failed to mention above, but Stu picked up on it, the house bank was pretty depleted (80%) after a few nights on board at anchor.

Swapped wires to feed house bank first, as instructed above, and after 1 hour motoring today the house bank charged up into mid 13's, combiner opened, start bank quickly topped off as well.

I'm confident under tomorrow's motor they'll combine instantly and I'll reach 14's and have them both ready for another few nights of drinking rum and listening to the Blues.

Thank you all again. Cheers.



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[svlamorocha]

Originally Posted by Maine Sail

Sounds like you are getting a very typical issue called "relay cycling" due to an incorrectly installed ACR, for the application..

Maine Sail and Don

Now the follow-on question for you... How does OP make sure that the alternator is sensing voltage from the right battery when uncombined?

Or do you presume that ACR is working in auto mode, hence:

- in uncombined state means voltage in BOTH batteries is below 13.X volts, hence you do not care about which one is being sensed; and

- in combined state then both batteries have the same voltage, hence it does not matter which one you are sensing from?

Thanks in advance for the wisdom..

[smac999]

his old setup should have worked fine. (and did for 2 years) his house bank is small and no cycling should happen if everything is ok. I only see cycling on 800+ah house banks with small alts.


now he has masked the problem but not solved it.. now he is motoring for an hour before the start gets any charge.. the probem will keep getting worse and someday the start battery won't get any and you'll be dead in the water from draining the start battry while motoring. I would figure out what the problem was. not band aid it by moving wires around. one of the banks might be weak. But I'm guessing the alt is dying.

Originally Posted by mariner36bob

The Amps increase to 12-20 amps, the house bank voltage begins to rise into 13's....still looking good...

Meanwhile the Start battery falls to 12.7-12.8 and combiner kicks off.

if your house is over 13v and your and start is 12.7 before the combiner kicks off then you have bad ACR wiring or a bad ground between batteries. with the combiner on they should be identical.