Question about 12v charging setup for a trolling battery

[rbstern]

I've got an onboard 12v deep cycle trolling motor battery that I need to charge at a dock that is away from grid power. My plan is to use a 40 watt panel, connected to a 6.6 amp Steca Solsum 12/24v charge controller.

The Steca has two sets of output terminals: 1 for a load (lighting, etc.), 1 for battery charging.

If I wanted to maintain a second 12v battery in the dock box for things like lights, radio, etc., would there be a disadvantage to rigging the in-box battery to the charge controller, and then charging the boat mounted battery from the box battery? Will there be battery equalization issues when the sun is not shining?

I could also run the charge leads from the Steca to an A/B battery switch, and selectively charge the boat or dock battery as needed, but it's just one more thing to keep track of.

Thanks for any input.

[Naptown]

I've got an onboard 12v deep cycle trolling motor battery that I need to charge at a dock that is away from grid power. My plan is to use a 40 watt panel, connected to a 6.6 amp Steca Solsum 12/24v charge controller.

The Steca has two sets of output terminals: 1 for a load (lighting, etc.), 1 for battery charging.

If I wanted to maintain a second 12v battery in the dock box for things like lights, radio, etc., would there be a disadvantage to rigging the in-box battery to the charge controller, and then charging the boat mounted battery from the box battery? Will there be battery equalization issues when the sun is not shining?

I could also run the charge leads from the Steca to an A/B battery switch, and selectively charge the boat or dock battery as needed, but it's just one more thing to keep track of.

Thanks for any input.

The red would be a better option Connecting both batteries together could be a problem but I am not a battery guy. Perhaps Sunking will respond.

[Sunking]

How often will you be using the batteries?

I do not know what size batteries you have but if they are the standard Marine Trolling Motor battery of 12 volts @ 100 to 150 AH, it could take a few days to recharge one with that small of a panel.

[rbstern]

How often will you be using the batteries?

I do not know what size batteries you have but if they are the standard Marine Trolling Motor battery of 12 volts @ 100 to 150 AH, it could take a few days to recharge one with that small of a panel.

Don't know the AH off hand, but they are group 27 size batteries, so your estimate is a decent guess.

Batteries will not be in use often. The dock battery will be very lightly used. The trolling battery might rarely be discharged to 50 to 60%. More often not below 80%, and the boat will sit, plugged in and charging for days at a time. The boat gets used an average of once or twice a week during spring and summer, for a couple of hours at a time, usually on weekends. Solar panel will be in southern facing orientation and will get a lot of Georgia sun where it sits. Not really worried about the amps. It will be enough due to low usage.

My greater concern is whether charging the batteries as a single 12v bank will be a problem. If the boat battery is modestly depleted, will it it draw too much current from the dock battery when put in parallel? I had not planned on heavy duty cabling, and the cables will probably be about 10' long.

[Mike90250]

The proposed panel, is too small to recharge a trolling motor battery. By the time (4 or 5 days) it recharges it, the battery will have suffered damage. But that's ok, if you can stand to replace the battery every year or 2.
It would be ok for the dock battery ( a night light to aim for home with ?)
You would need 2 panels, and 2 controllers.

[Legacy]

you could also use a larger panel and the Morningstar Sunsaver Duo
charge controller,with it you can set charging priority on two seperate
batteries http://www.morningstarcorp.com/en/sun-saver-duo

[rbstern]

The proposed panel, is too small to recharge a trolling motor battery. By the time (4 or 5 days) it recharges it, the battery will have suffered damage. But that's ok, if you can stand to replace the battery every year or 2.

I've subjected deep cycle batteries to far worse conditions (deeper discharges, long periods of not being restored to full charge) and have never had one go bad in 2 years. I've had trolling batteries sit at a partially discharged state for six months at a time, no charging at all. I don't think I've ever had a flooded deep cycle battery last less than four years, and I usually get five or six years out of them. Am I sacrificing some battery life with less than ideal handling? Probably. But these things aren't exactly fragile.

I expect the battery will typically be recharged in 2 days or less (conservatively, 15 amps per day; sun here is brutal in the summer).

I'll follow up this thread with some performance examples once it's set up. I'm thinking I will probably just start with the trolling battery, and leave the dock battery out of the equation for the moment. I can either add another panel and controller, or the A/B switch, somewhere down the road.

[Mike90250]

Battery Sulfation

when lead/acid batteries get below 80% full, the sulphate in the acid, begins to settle out and crystalize on the plates. Within a day or so, it can be reversed and driven back into solution, That's what makes the specific gravity change in the battery.

After about 2 days, the crystals harden, and become extremelly difficult to dissolve. This causes reduced battery capacity in 2 ways:
a) electrolyte is starved because the sulphate crystals have locked up the sulfur
b) plate areas is reduced because of the crystals attached, obscuring surface area.

There are many schemes for de-sulfation of batteries, but they are generally hit or miss, salvage efforts.

more reading

http://rollsbatteryne.com/docs/A%20Sulfated%20Battery.pdf

http://jgdarden.com/batteryfaq/carfaq16.htm

http://www.roperld.com/science/batterysulfation.htm

http://www.batterystuff.com/kb/articles/battery-articles/battery-basics.html

[rbstern]

you could also use a larger panel and the Morningstar Sunsaver Duo
charge controller,with it you can set charging priority on two seperate
batteries http://www.morningstarcorp.com/en/sun-saver-duo

Meant to include in my previous response: Thanks for pointing this charger out. That's a handy option for future projects.

[rbstern]

when lead/acid batteries get below 80% full, the sulphate in the acid, begins to settle out and crystalize on the plates. Within a day or so, it can be reversed and driven back into solution, That's what makes the specific gravity change in the battery.

After about 2 days, the crystals harden, and become extremelly difficult to dissolve. This causes reduced battery capacity in 2 ways:
a) electrolyte is starved because the sulphate crystals have locked up the sulfur
b) plate areas is reduced because of the crystals attached, obscuring surface area.

There are many schemes for de-sulfation of batteries, but they are generally hit or miss, salvage efforts.

more reading

http://rollsbatteryne.com/docs/A%20Sulfated%20Battery.pdf

http://jgdarden.com/batteryfaq/carfaq16.htm

http://www.roperld.com/science/batterysulfation.htm

http://www.batterystuff.com/kb/artic...ry-basics.html

Mike, I don't dispute the technical accuracy of the info in the links above. But it's a bit overdone for a $100 battery.

For the last fifteen years, I've had consumer-grade, deep cycle batteries in a half dozen different boats. Either group 24 or group 27 sizes. Interstate, Trojan, Everstart (Walmart), Bass Pro store brand, West Marine store brand, Advance Auto's store brand. I've subjected them to FAR worse care than what is recommended in the links above. Only one battery suffered what I would call premature failure: the Trojan. But that battery was onboard a two model year old leftover boat; I think it had been sitting discharged for two years before it came to me, and was about four years old when it wouldn't hold a charge anymore. The Interstate that replaced it is working fine going into it's fifth season, and nobody would accuse me of taking particularly good care of it.

If I was maintaining a $4000 bank of batteries, I'd certainly invest time, money and effort worrying about optimizing the battery chemistry. I have a golf cart with 4x12v Trojans, and for those, I do invest a bit of effort to keep them healthy.

Perhaps, if I used the boat batteries harder, like a tournament fisherman does, I'd see less battery life. But these batteries are almost never pressed very hard in the roles I use them.

[Sunking]

Perhaps, if I used the boat batteries harder, like a tournament fisherman does, I'd see less battery life. But these batteries are almost never pressed very hard in the roles I use them.

Then you really do not know how much capacity they might have lost. Pro Walking Bill Board Fisherman don't worry about abusing batteries, they are free. Not too mention are likely also being recharged by the boat motor with that 300 HP engine pushing their boat. Bet their sponsors can afford a battery isolator.

[rbstern]

I ran an experiment over the weekend to test the above mentioned setup.

I took a fully charged, group 24 85 amp/hour Kirkland (Costco) deep cycle battery and drained about 18 amps from it via an inverter and a 75 watt lightbulb. Ammeter showed 7 amp draw rate for that setup, so I let it run for 2.5 hours. Approximately 20%.

I then set up the 40 watt panel and Steca charge controller outside yesterday (Saturday). The test locaion was limited to sun from about 11am to 5pm. When I first hooked it up, the ammeter showed the charge rate was about 2.7 amps during unobscured sun. Yesterday was a bit hazy, with partial clouds, and this would dip to 1 to 1.5 amps during times when the sun was obscured or the haze got thick. I couldn't leave the setup outside overnight, because the charge controller isn't weatherproof and it was threatening rain last night. So I broke it down and then set it up again today. I estimate that battery got about 8 to 10 amps yesterday.

I repeated the setup today. The sky was very clear. The ammeter stayed pegged at about 2.76 to 2.78 amps. By about 3pm, the Steca controller's battery condition LED began to flash, indicating the battery was at full charge and the charger had switched to maintenance mode. The charge rate dropped back to about .75 amps, presumably a function of the charger's electronics.

So, in less than perfect conditions (no morning or late day sun exposure because of tree surroundings, which won't be the case when it's on a boat dock roof), a group 24 battery recovered from a 20% discharge in under about 10 hours of near full sun. That's very acceptable for my purposes. The panel, a Solar Cynergy 40 watt unit, is putting out about 10% above rated voltage. The Steca is rated for 6.6A, so if I ever feel the need to add a second panel, it's an easy change.

Picture of the setup just before the shadows hit it late today:

[Mike90250]

Congratulations, you have done what few will do. Actually test something.


The only flaw I see, is that a trolling motor will consume a lot more than 18ah.
I guess it depends on how far you go in the boat.

75W plus inverter losses, call it almost 100W of load, for a total of 250wh depletion / 12V = 21AH pretty close to your number of 18

Charging , call it 30 watts for 12 hours = 360 watts I'd call it pretty good I think.
360 * .8 288

[Sunking]

Let's see; a trolling motor on my boat uses around 50 to 100 amps trolling around.

[rbstern]

Let's see; a trolling motor on my boat uses around 50 to 100 amps trolling around.

According to specs, my Minn Kota 12v powerdrive draws 42 amps at full throttle. I rarely ever use it at full throttle. Most of our fishing is in wind protected coves where the trolling motor is used at less than half throttle, and even then, just intermittently to reposition the boat to the next dock or point. If it's rough, we tend to stay home. Definitely fair weather fisherman. I'd be really surprised if we used even 20 amps on one of our typical two to three hour outings. And in most cases, the boat will have four or five days to recover. If we use it hard, I can pull the battery and charge it via utility power. Or if I find the charging inadequate, I'll add another 40 watt panel. I'm sizing the wiring to handle 6 amps at < 3% loss, just in case.

We'll see how it works out between now and late in the year. I will post real world results.