Electronics die, perhapse after starting engine, recently 1 month off charger

[bonkle]

Everything seemed fine before the boat sat in dry dock for a month. When I picked it up, the engine started right up as normal, but my Raymarine Dragonfly 7 (not particularly advanced. It's a fish finder) and the oem depth sounder would not turn on. After motoring for 10 min, they'd turn on sporadically for a few seconds then turn off. I ended up flipping the breaker and not mess with them for that trip. Subsequent trips seemed fine (batteries on the tender when not sailing), but very occasionally I'll look up and the Dragonfly will be off. It also seems that it will turn off somewhat reliably after cranking the engine. It may even take a coule tries to boot- like the power is bobbling.

I have two, new-looking, group 31, AGM, "Marine Dual Purpose" batteries run in parallel. There's nothing at all fancy about the setup. Only one bank and no house/engine separator.

Question 1- What do you think the issue is here?
Question 2- What size battery should I dedicate to the engine should I install a 2 bank system? (Yanmar 2GMF, 2 cyl, 586cc)

 

[dlochner]

Many electronic devices will shut down if there is a voltage drop which can occur while starting the engine, likewise if the voltage is too low when they are turned on they will not turn on.

Unlike people, even dead batteries can look good. How old are the batteries? How have they been charged, what charger are you using? AGMs are especially sensitive to be left in less than a full charge. If these are West Marine/East Penn AGMs, they are not the most robust AGMs out there.

Check all the connections including DC- connections. Poor connections can cause voltage drops which is the likely cause of your symptoms.

I have a larger Yanmar, 3jh2e, and I start it off a Group 24 FLA battery. It doesn't take much to start the small diesels we have on sailboats.

There are a number of good articles on batteries and charging on MarineHowTo.com. Check it out.

 

[JamesG161]

Raymarine Dragonfly 7

Most Raymarine devices shut off when less than 12 VDC at the device, not just your battery VDC.

Sounds like you have a lose connection on your Dragonfly.
Jim...

 

[Don S/V ILLusion]

When was the last time you checked all the wiring and particularly the integrity of all power connections?

 

[bonkle]

When was the last time you checked all the wiring and particularly the integrity of all power connections?

I haven't really checked connections well... Just a visual. Alternator reads good though. I should probably disconnect everything, give it a scrub, and put on some kind of corrosion inhibitor. One thing I just put together is that the batteries are in paralell, but there's a 2 bank tender- one on each battery. Wonder if that's bad. The tender may be this Deltran 1.25A model (or older version).

2 Bank, 1.25 AMP 12V Battery Charger

-Dimensions: 7" x 4.75" x 3.5"-Weight: 3.14 lbs-AC Power Cord Length: 6 ft.- 18 AWG-DC Output Cord Length: 4.5 ft. - 18 AWG-DC Output Accessory Length: 1.5 ft.-12 volts @ 1.25 AMPs per station.Included in the box: One 2 Bank Multibank Charger Unit, two separate alligator combo clips

www.deltran-global.com

Edit: Batteries are F* expensive!!!!!!! Last time I bought a battery for a little econo-box car I think i paid $80. I can't seem to find anything under $150 now!

 

[kloudie1]

An accurate voltmeter is necessary to get a better understanding of battery state of charge and voltage drop.. Somethng in the $30 range (Amazon or equivalent) is probably sufficient.. then check out some of Maine Sail's articles:
Under-Load Battery Voltage vs. SoC - Marine How To

 

[jviss]

Unlike people, even dead batteries can look good.

Quote of the day.

 

[JamesG161]

Batteries are F* expensive!!!!!!! Last time I bought a battery for a little econo-box car I think i paid $80. I can't seem to find anything under $150 now!

You might switch battery types and save $$

EverStart Lead Acid Marine & RV Deep Cycle Battery, Group Size 27DC (12 Volt/750 MCA) - Walmart.com

$97

Jim...

 

[jviss]

Edit: Batteries are F* expensive!!!!!!! Last time I bought a battery for a little econo-box car I think i paid $80. I can't seem to find anything under $150 now!

Ha! A genuine deep cycle battery, like a Trojan group 27 115Ah FLA (flooded lead acid) battery is in the $265 neighborhood!

I bought not so serious deep cycles this year two group 27 Everstart (WalMart), model 27DC, 109Ah. They weight nearly what the Trojans did, 52 lb. vs. 60. And, they have April 2023 date codes. The keys to buying deep cycle FLAs are weight and age. Look at the date codes! Mine were $94 each.

 

[dlochner]

In battery health there are 2 factors to consider, State of Charge (SOC) and Capacity (Balmar calls this health). Resting voltage, i.e, no load and no charge for 24 hours will estimate SOC. However, the more important factor is capacity. Over time batteries decay through use. With each charge/discharge cycle a little capacity is lost. After a few years a 100 ah Group 31 battery will no longer have 100ah capacity, it will be much lower. For AGMs cycles are important as well as the charging protocol and time spent in a partial state of charge (PSOC). Either of these, especially long periods in a PSOC state are deadly for the AGM batteries. Repeatedly drawing the SOC down below 50% of capacity is also deadly.

If the electrical connections are tight and clean, the issue is probably the batteries. There may be a date label on the batteries, it would be good to know how old they really are.

AGM batteries may not be the best choice for you. You have to look at how you will use the battery, how it will be charged, and what you can afford. You are correct, the price of AGMs is quite high. Also, if you parallel the batteries, they need to be equally charged, of the same chemistry, of the same age. If there is an imbalance in the batteries, i.e., one old, one new, the bank will sink to the state of the weaker battery.

When your boat was built 40 years ago, electrical needs were quite simple, running lights, cabin lights, maybe a VHF. Heck, LORAN-C was an expensive luxury in 1983. The electrical system on these boats is wholly inadequate for what many of us now consider essential, pressure water, chart plotters, autopilots, AIS VHF, etc etc.