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Old 22-03-2018, 13:23   #1
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Trickle Charge Batteries in Summer MX Dry Storage

New to forum, so forgive any redundancy. Am planning so trickle charge my two batteries during summer storage in San Carlos, MX. 25 volt solar panel to controller to batteries. Advice?
-Doc
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Old 23-03-2018, 08:53   #2
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Re: Trickle Charge Batteries in Summer MX Dry Storage

Have read a number of posts on battery storage in extreme weather. Thanks Forum mates! Appear to be two basic concepts here: either disconnect batteries for storage time (seems to work best with sealed gel batts) or trickle a solar charge with good controller (appears best with plate/water batts). I will experiment with both approaches and report back. Am planning to sail from San Carlos and repeat Sea of Cortez experience of 30 years ago in a 17" Venture with swing keel - no electronics - no maps - really stupid! Now own a Tanzer 27 with lots of electronics and cell coverage (T-Mobile). Still looking for the maps.
-Doc
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Old 23-03-2018, 11:44   #3
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Re: Trickle Charge Batteries in Summer MX Dry Storage

> disconnect batteries for storage time

Actually nothing to do with type, lead is lead.

With GEL, just as important to keep them well topped up, even if a bank has a slower self-discharge rate you have to stay ahead of it, and the more expensive and sensitive the chemistry the more true.

With FLA you risk letting water go low as well, since you have to visit for that might as well top up manually too.

Leaving any batt live charging unattended is putting a lot of trust in the regulation gear.

Exception is such a small solar input it can't contribute much more than the self-discharge rate anyway.

But I'd still check on it if a failure would hurt my wallet.
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Old 23-03-2018, 14:22   #4
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Re: Trickle Charge Batteries in Summer MX Dry Storage

John61: Thanks for input! As boat sits in dry storage now, no load(s) on batteries. Need to disconnect? Can you give a rationale? - are we worried about override of off switch? Am thinking of an experiment for this summer - disconnect Gel battery and trickle the FLA after top off. Gel is sealed - how to top that one off and how if so?
My main concern is the intense heat and its effect on batteries. One old salt told me he left batteries over summer and came back to completely dead cells. Plan is to dry-store boat mid-June to early October each year.
What are the horror stories of trickle equipment malfunctions? I'm using NewPowa 25V solar panel with Allpowers 20A controller - right now I'm getting .1 amp to a battery in Colorado. Thanks again for comments.
-Doc
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Old 23-03-2018, 19:21   #5
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Re: Trickle Charge Batteries in Summer MX Dry Storage

Yes when unattended, all loads disconnected is best, however done.

Yes heat kills longevity, true for any chemistry. Yes left for months with no care can murder them.

Sealed batts only need regular charge top off if not Float charged, FLA also check water each visit.

"Trickle" equipment implies cheap, even automotive gear, poor regulation = death.

Get a proper marine deep cycling mains charger, usually costs more $ than the bank, but a once off investment, batts are consumables.

Never heard of that controller, would be nervous trusting unattended if the bank is expensive.
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Old 23-03-2018, 19:50   #6
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Re: Trickle Charge Batteries in Summer MX Dry Storage

Thanks John61. Will definitely disconnect. Will report in early October. Previous experience has been dry-store sailboat and shore power on trawler in Anacortes. Weather not really a problem and never disconnected sailboat batts - never an issue. Dry storage and intense heat is new experience (sold the trawler and took sailboat to MX.) I have about $350 in house and engine batteries - total - 27s. Not like these are Trojans.
Thanks again.
-Doc
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Old 23-03-2018, 21:16   #7
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Re: Trickle Charge Batteries in Summer MX Dry Storage

And even Trojans aren't premium really, many boats have thousands invested just in the House bank.
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Old 24-03-2018, 12:46   #8
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Re: Trickle Charge Batteries in Summer MX Dry Storage

In tropical conditions on the hard it is best to have a solar controller that charges a maximum of 13.2-13.3V for wet cell batteries. This is because the batteries will begin to produce gas bubbles and evaporate off the water at higher voltages. Few solar controllers have a 13.2V setting. Most have 13.7V float settings.

You could trick the controller by adding a Schottky diode (or isolator) between the controller and the battery. With a good Schottky diode the voltage drop is around 0.45-0.55V at trickle current. The solar controller woud see 13.7V on the controller side of the diode and the battery would see ~13.2V on the battery side. If I were doing this I'd order a MBR40250G diode from Digikey or Mouser for less than $2/ea. I'd cut off the left pin (1) since that is the same as the tab (with the hole). I'd connect the tab to the battery positive and the right pin (3) to the solar controller. Take care not to let the back of the diode or the tab get near any ground. Don't tape the back of the diode or the tab, since that's where it will give off heat if the controller starts a 3-stage charge cycle.

You could use a regular battery isolator but the voltage drop would be around 0.7V.

For AGM batteries, I'd just use the controller 13.7V setting since that is close to float.
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Old 24-03-2018, 14:40   #9
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Re: Trickle Charge Batteries in Summer MX Dry Storage

Locquatious: thanks for info. Can I take a diode off of an old desktop computer? I have a couple of months to experiment. Why is the fluid boiling off? Does the battery get that hot? We are looking at maybe 120F max inside battery compartment, with venting, based on anecdotal info. Do I need t worry about other electronics (radio, inverter, chartplotter)?
-Doc
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Old 24-03-2018, 15:14   #10
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Re: Trickle Charge Batteries in Summer MX Dry Storage

Quote:
Originally Posted by drjoshua View Post
Can I take a diode off of an old desktop computer? I have a couple of months to experiment. Why is the fluid boiling off? Does the battery get that hot? We are looking at maybe 120F max inside battery compartment, with venting, based on anecdotal info. Do I need t worry about other electronics (radio, inverter, chartplotter)?
-Doc
You might find a rectifier diode on a computer, but you won't know the specs. Digikey and Mouser ship quickly, at least in the US. I was looking at Vf (voltage forward), current capacity (20-40 amps depending on your solar capacity), and voltage rating of at least 20V for a 12V battery. Keep in mind that if you have a major rain storm, there will be little charging and the bilge pump may run down a battery. When the sun comes out again, your panels will put out full amperage for a long time.
Good question on bubbling. My bubble-temp info is from a chart for an old controller. I built my own solar controller and put in the 13.2V setting. Never had dry batteries again. Speculating it is a combination of the heat and chemical conversion. At lower temperatures, the gases reabsorb into the electrolyte. The battery at trickle is probably just above ambient. 120F seems high and would decrease battery life.

The diode is only for long term trickle-charge solar charging. I would disconnect or switch off other unnecessary loads (radio, inverter, chartplotter, instruments, LED's, anything with a quiescent current rating above a milliamp), but leave on things like the autobilge.
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Old 24-03-2018, 22:25   #11
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Re: Trickle Charge Batteries in Summer MX Dry Storage

You should be OK on any type of battery if you have set the solar controller to proper setting for your battery type and you limit your solar output. Adjust panels to provide only about 500mA per 100AH battery capacity then even if your controller goes unregulated, you won't harm the batteries.

If you want an anchor light on while you are gone, you need to those AH into the expected solar output.
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Old 25-03-2018, 06:32   #12
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Re: Trickle Charge Batteries in Summer MX Dry Storage

I am doing the same in San Carlos. One 100 watt panel and a good controller to stay and trickle some into the house bank. The engine battery I will take north and bring back when we return in the Fall.
I had two 27s for engine batteries and they both died after a year without a charger. I replaced them with a new 31, which is doing fine.
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Old 26-03-2018, 21:06   #13
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Re: Trickle Charge Batteries in Summer MX Dry Storage

Leaving batteries over winter is a complex and controversial subject with several options. Here are my thoughts.

Option 1.
For many the simplest solution is just leave their batteries disconnected from any loads for 6 months and they are pleased if they are still at 12.5v when they return. What they don’t realise is the damage to the Ah capacity this has caused, because all batteries need some charging over the winter to compensate for their self-discharge. Even if the main isolator switch is shut off some loads may still be directly connected to the battery, like a bilge pump or the memory on a car radio/CD player. Even these very small loads will accelerate the self discharge, especially over a long layup.

Self-discharge is dependent on battery temperature and the age of the battery, AGMs and Gels self discharge only 2% a month, but Flooded Lead Acid, may be as much as 10% a month. Cold winters mean less self discharge.

After 6 months the effect of any self discharge means parts of the battery plates will have permanently sulfated because the lead sulfate crystals that are part of normal discharge will have hardened. A 100Ah battery will no longer deliver 100Ah!

Option 2.
Solar panels, even small ones, can easily keep the batteries full charged, but if left connected for 6 months when all loads on the boat are switched off they can “overcharge” and “boil” batteries even with a quality solar controller. This happens because every night solar provides no power and switches off, when they sun is up the controller switches on and goes straight into bulk mode. Because the batteries are almost 100% full they very quickly reach absorption which takes the battery up to the gassing voltage of about 14.4v. A battery is normally happy to sit at this voltage whilst it is charging as the gassing is very slight which helps to stir up the electrolyte and remove sulfation. But even smart controllers are pretty dumb, most don't know the battery is really almost fully charged so when it automatically kicks into absorption it may stay there for the pre-programmed time period of up to 3 hours before it drops to float. The battery won’t be taking any current when it is full but it’s the voltage that does the damage, especially if applied for three hours everyday for 6 months to already fully charged batteries!

Option 3.
Others leave their shorepower connected and maybe a light left on and they return to find the cable removed and the batteries flat, or to find a battery has a bad cell which has boiled dry and set fire to the boat. Better to have someone reliable connect shorepower once a month for 24 hours and cheque the batteries are all right.

So none of the these options are ideal!

The key message is all chargers, especially shore power, should be programmable if they are being left over winter. Set the solar absorption voltage lower than normal at about 14.0v and set the absorption time to about 20 minutes. When it comes on its below the gassing voltage but will give a battery a bit of a boost to stir up the electrolyte and avoid stratification. Below 14.4v there will be no gassing at normal temperatures.

Shorepower chargers like a Victron can also be set to limit the current to a couple of amps to stop the batteries boiling if there is a shorted cell.
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