Battery voltage drop during trolling?

[Hydraulicjump]

Here is a mystery for the Tugnut electrical wizards. We are just back from a two week Desolation Sound/Discovery Islands cruise with a freezer full of salmon and ling cod. We trolled a lot and ran into some weird battery voltage changes. Seeking ideas to the origins of the problem and if there is anything to worry and/or do about it. Here are the particulars:

1) After about an hour of trolling at forward idle speed with the (mostly useless) trolling valve out (get a kicker), we noticed that the house battery voltage would start to decline rapidly. This was easy to follow using the Morningstar monitor for our solar panel. Over the space of a half hour the voltage would go from fully charged (12.8) to 12.2.

2) All normal electronics were on, including a split screen view of sonar and charts, but nothing else was in use (we have a hand crank downrigger).

3) This could be "corrected" by shutting off the engine and restarting it, forcing the charger to go through its voltage check and charge cycle (?). Alternatively, we could stop trolling and drive the boat hard to get this to change. There were no alarms regarding issues with the alternator, although I am unsure whether that has an alarm. Goodness knows everything else on the engine does.

4) Following each of these episodes the batteries were charged up nicely by the solar panel and showed no sign of an inability to hold the charge, keeping the fridge going all night with plenty of reserve storage come the morning. All systems normal. Batteries are AGM and on their fourth season.

5) Most perplexing of all, this was not reproducible. We trolled every day for about 10 straight days and this happened only three times. All on sunny days when the solar panel was working fine, producing plenty of amps. It almost seems like the charger just plain forgot about the house batteries or, worse yet, the alternator was not producing enough juice in idle (seems unlikely).

Any ideas?

 

[knotflying]

I am by far not an electrical wizard and I am sure others will chime in here, but your charger is not operating while under way. Your alternator should be charging your batteries and the relays open and close based on which batteries need charging. However, if the relays sense something is wrong with one of the battery banks they will not allow the batteries to connect and hence charge. So my first thought is that you may have a bad battery, but then you say when you are on the hook everything seems to hold charge.
The other thing I question is your voltage readings. When the engine is running you should have a much higher voltage reading than 12.8 volts. Usually with a surface charge while running the engine I get a reading as high as 14 volts or better.

 

[SGIDAVE]

Hello HJ,

So, you are trolling which means your main diesel engine is running at "low" rpm's, correct? Even at 1000 rpm your alternator should be putting out good charge current.

As Mike says, your battery charger (the one that runs on 120VAC or genset or shore power) should NOT be energised whilst trolling. If it IS running, well, then it must be using the inverter to convert 12VDC to 120VAC (to power the battery charger) back to 12VDC and that is NOT what you want happening while underway.

The alternator on the main diesel should be charging ALL your batteries after a few minutes of operation. Look here (http://www.bluesea.com/products/7610/SI ... 4V_DC_120A) for the Blue Sea informational page for the Automatic Charging Relay (ACR). Note there is a pdf document you can download called the "Diagnostic Flowchart" located under the "Installation tab on the right side of the page. This is worth downloading, printing and adding to your ONBOARD paperwork since it will help you troubleshoot.

Anyway, IF the alternator is functioning properly, it should be producing a charging current which exceeds 13VDC (probably closer to 14VDC as Mike says above especially if your batteries are "LOW"). This charging current should first be directed to your "Starting" battery. (You can trace the output wire from the alternator to....a battery somewhere...and it SHOULD be the start battery. The ACR should "combine" the start and house banks after it detects a charge voltage of 13VDC for 90 seconds or greater voltages for lesser time.

If my thinking is correct, and it frequently IS NOT, there are TWO KEY elements in the "charge while trolling" scenario. The ALTERNATOR and the ACR. EITHER the alternator is NOT putting out proper current (i.e., a bad voltage regulator) or the ACR is not properly responding the the charge current. Of course there are other elements in this charging circuit that could booger things up, but the ACR and Alternator are the key mechanical/electronic components. Loose or corroded connections or cable terminations may be involved too.

Next time your trolling, get out your VOM and check the voltage of the START battery. If the alternator is working, it should be 13-14VDC. If, while you get a measurement like that and you simultaneously have a "low" reading on the house battery bank (like the 12.2VDC you mentioned) then you KNOW the ACR is not combining the batteries properly. It may be a hinky ACR combined with a weak battery within the house bank causing it to drop from 12.8VDC to 12.2 in half hour of light use.

Again, simple testing with your VOM will help isolate the problem.

Let us know what you find!

Fair Winds and Charged Batteries,

/dave

 

[HRowland]

A clarification to what Dave said- on your 2011 R27 the engine alternator is most likely connected to the house battery bank. This makes sense because it is most likely to need charging the most. The Automatic Charge Relays will combine the house and engine, then the engine and thruster batteries when charging voltage is present. See the Blue Sea site for the ACR details, basically when over 13V they will combine (after a delay). There can be a lockout if a battery is very low, there is a LED on the front of the ACR to indicate status- off is open, on is combined, and blinking indicates a lockout state. You can also use the voltmeter on your DC panel at the helm, when charging and ACRs have combined the banks all three positions will read the same voltage. On my R27 (yours is likely the same) position 1 is engine, 2 is house, and 3 is the thruster battery voltage.

Since you are seeing less than 13V it does not appear that the alternator is charging the house battery. Unless the house battery is significantly discharged the voltage will increase to over 13V in a fairly short time, then as the battery gets more fully charged it will rise to slightly over 14V and remain while the engine is running. I see 14.2-14.3V or so when the batteries are fully charged and the engine is running.

Even at idle the alternator on the Yanmar BY2 series can output significant current. I have a battery monitor on my combined house/thruster bank, when moderately discharged I see charge currents of over 80A at idle. You should have no issue idling all day long.

I would check the cable and connections on the alternator and batteries. There should be a cable labeled alternator on one of the house batteries, or you can follow the large red cable from the alternator into the battery compartment. All connections should be clean and tight. Also check the ground cable on the engine block since this carries the return current to the alternator, although if this had a problem you would have difficulty starting. Make sure the alternator belt is tight, there is an automatic tensioner on this belt. However, if this belt was loose you might also be overheating since it also runs the engine internal coolant water pump. If everything is OK but still no charging voltage the alternator may have failed.

Howard

 

[Hydraulicjump]

Thanks you guys. This is hugely useful. I will investigate this and report back. I view this as an opportunity to go fishing. The salmon are arriving here in California, so the timing is good.

Again, thanks so much!

Jeff

 

[Spacetrucker]

Have all your battery's tested first. You my have a bad one or bad cells. So ck them with a heavy battery tester first. Sound like 1 or2 my be going down. T change all batters Avery 1.5 years. But you did not say , that the boat is use all the time or just short time. Bat I use battrey jun on them all when not on the boat. Also gave solor bat in stall. Sorry for spelling but Rockne and roll on the water to day here in canad good winds for shure.. Let us know.