[MedSailor]

I was thinking of adding a 12v battery system to my Portland Pudgy tender. Mostly it's because I want to tinker, rather than have it be really useful. What I have in mind is a 2-5Ah or less, sealed 12V lead acid battery, a small panel, 12V charger, nav lights etc. My question though, is how do I charge a sealed lead acid battery? Don't they explode if over-charged? Are there small solar or controller setups that would work?

MedSailor

 

[btrayfors]

Yes, there are small solar controllers which would do the trick for you. They can be set for type of battery.

Genasun makes a line of such products...they are popular and well made. The little 4A one starts at just under $60 street price.

Bill

 

[Bill-Rangatira]

with sealed batteries the trick is to keep the charging voltage low i have 2 20 ah for running my dinghy electric motor on charging on in use and charge 13.7 volt instead of the 14.4 most chargers do, at that voltage the amperage is not an issue and they will not overcharge

 

[btrayfors]

At 13.7VDC you're likely not getting a full charge.

The trick with ANY battery, sealed or not, is to charge and float at the recommended voltages.

For gelled batteries, this is often 14.2VDC absorption and 13.6VDC float.

For AGM batteries, this is often 14.6-14.8VDC absorption and 13.8 float.

For flooded batteries, this is often as high as 14.8-15VDC absorption and 13.6 float.

Check the recommended voltages for your specific batteries.

Note: manufacturer's recommended voltages are often quite conservative.

Bill

 

[MedSailor]

This is interesting, with good information about voltages and such, but how do I put this in practice on this small scale?

 

[Zanshin]

As has been mentioned above, you need to ensure that you charge at the right voltages for the right amount of time; this means you should use a battery charger. The Genasun line of MPPT and PWM controllers will do this. I also just saw a new line of Solbian solar panels with built-in 12V smart chargers that might fit your bill - ALLinONE series

 

[Minnewaska]

I had a similar desire to keep a motorcycle battery charged. It is stored in a shed away from power, so I researched solar panels and charge controllers. They were fairly readily available.

However, here's a lesson learned. When the panel I ordered arrived, it had a disclaimer on the first page........ Do not expose panel to the elements. Seriously. Wtf? I guess it was a panel designed to be left on the dash of your car, not outside. I sent it back and haven't reordered a different manufacturer yet.

 

[MedSailor]

I think I'm getting it now. I generally am aware of what a MPPT controller is, and I know they're the bees knees for solar, but I think I see how that would work for my application. I was imagining charging by connecting to the boat, through a charger with solar as an adjunct (as it often is) but with such a small capacity, I can see how solar would suffice as a primary.

That brings up a question, does an MPPT controller know, or care what it's charge input source is? Could I have one source be a solar panel and another be a 12v plug that connects to the boat somehow when she's on her davits?

Thanks for the replies so far.

MedSailor

 

[Noelex]

A very simple method that works reasonably in practice is to simply parallel your gel battery with your normal battery bank when it being charged, but in addition add a diode (plus fuse).

The diode will drop the charge voltage by about 0.5v. Thus the normal bulk voltage for the flooded house battery of 14.6-14.7, becomes 14.1-14.2v. The float voltage of 13.7 becomes 13.2v. These voltages are close enough that the gel battery will get a reasonable charge. The gel batteries are cheap enough that that a slightly less than perfect charge algorithm is not a great concern.

A suitable diode will be less than dollar, you can even scrounge one from some old defective electronics.

 

[PitApe]

As far as I know, most or all of the small sealed lead-acid units are AGM (absorbent glass mat) batteries. If you have a small solar charge controller it should have some way to regulate the voltages for AGM batteries. Just set it to the AGM option and let 'er rip.

 

[Zanshin]

As far as I know, most or all of the small sealed lead-acid units are AGM (absorbent glass mat) batteries...

Unfortunately not all, or even most, sealed units are AGM. Just point at just one example, see Batteries - Electricity on board for a page with both sealed maintenance free batteries (which I happen to have just purchased) and their AGM line. Charging a sealed battery that is not AGM with an AGM regimen will probably kill the batteries quite quickly.

 

[hellosailor]

2-5Ah is a wide range. That's an exit lighting or alarm battery and they're pretty much all AGM batteries for the last decade or two. If there are no specs, treat it as AGM.

I wouldn't waste money on an MPPT controller for a $10 battery. Figure out what size it is (2A/ 5A?) divide by ten and charge it at the 1/10thC rate with any simple charger and you should be OK, at least safe enough not to blow it up. Something cheap like a "battery tender" would still be overkill. 13.8-14.4, do you plan to charge manually after use? Or just keep a "conditioner" on it to keep it topped up?

These little ones tend to have a total four year life, btw. With continuous float charging (as in a UPS) they still dry out and lose about 25% capacity every year. And they take another 25% loss in hot weather, i.e. heat spells at 95-100F. So...I know some last forever but the question is, how much do you want to invest in a ten dollar battery to begin with?

 

[LinekinBayCD]

Check out the Battery Tender products the documentation indicates that the pannel can not be submerged but nothing about keeping it out of the elements.

021-1163

 

[PitApe]

Unfortunately not all, or even most, sealed units are AGM. Just point at just one example, see Batteries - Electricity on board for a page with both sealed maintenance free batteries (which I happen to have just purchased) and their AGM line. Charging a sealed battery that is not AGM with an AGM regimen will probably kill the batteries quite quickly.

Sure. Maintenance-free starting batteries for cars are usually not AGM, but the OP mentioned 2-5 Ah batteries. These tend to be small AGMs. Like these.

 

[gregcorey]

Since you are only wanting 2-5Ah, I would recommend GoalZero Solar. They have a number of really rugged solar panels that are either portable or mountable (they just released a 90W panel) I use 2 Boulder 30.

They also have some very excellent batteries, of which I've purchased many. And, apropos to this community, they just released a waterproof, 7Ah battery called the Veture 30.

Their stuff is maybe a little on the expensive side, but it is well designed and useful.

I use these mainly to run my GPS while on boat and keep my phone charged etc. I purchased a bigger boat recently so I'm in the process of planning something similar.

Greg

 

[Bill-Rangatira]

http://batteryuniversity.com/learn/article/charging_the_lead_acid_battery