Battery maintainer sizing

[Ashful]

I've had three Battery Tender brand solar charger and maintainers fail on me, over the last six years. I've also managed to incur some damage to four expensive deep cycle marine batteries, by having the batteries exposed to very cold weather while connected to a dead maintainer, having failed to notice on two of the three occasions when the maintainer actually died. I need to find another solution.

Here is what I had been using: Amazon product ASIN B004Q820TQ
My battery array is (currently) two 200 Ah marine deep cycle batteries, in the 20DC group size, connected in parallel. I do not use the solar maintainer to charge the batteries, other than perhaps the odd occasion when the batteries are low after a day's work. Its intended purpose and sizing is to be for battery maintenance only, preventing cold weather damage and freezing of these batteries which may sit several months between uses. I don't want the thing sitting every afternoon at 5 amps of charge current, as I anticipate that will not yield best battery lifetime.

In shopping for a replacement, there are commonly sizes spanning a nearly 40:1 ratio (5 watts to 200 watts), with no good information I can find on sizing one for maintenance. I know the advertised size is also a theoretical maximum, affected by latitude, tree cover, all the usual solar factors. It is also not clear what relation the array has on maximum charging current, if we are always safe on buying the largest array and just letting the charge controller circuit manage charge level.

Anyone have good knowledge on these?

 

[EatenByLimestone]

I move my batteries into the basement and then rotate the tester/maintainer down the row of them when I remember to move it. It’s not a solar thing, it runs on regular old electrons from the wall.

 

[Ashful]

I've debated doing this, but the way I have them presently mounted on the trailer makes connection/disconnection a rather hazardous affair. It's rock-solid in operation, but I did not consider ease and safety of replacement when I built this rig. I have plans to reconfigure, moving the batteries aft of the axles for better weight balance, but it never comes to the top of my ever-churning priorities list. Also, group 29DC deep cycle batteries aren't exactly feathers, no matter how they're mounted. Before this set, I had a pair of group 34's.

Keeping a maintainer on them in cold outdoor storage can be reasonably effective, if the damn maintainer doesn't die every two years.

 

[zrock]

What i did with my travel trailer is make a quick connect that is compatible with my solar panel and trickle charger, takes 2 seconds to set up.. If your batteries are fully charges they should not be getting damaged by cold weather. I was going to leave my solar panel hooked up for the winter but then it would sit out where it can get damaged so ill just toss one of my spare maintainers on it. I have had issues with the noco series of battery maintainers only lasting a few years, so this year a switched up to a matercraft series..

Personally if it was me and this was a daily use/job trailer i would wire a maintainer in permanently and make it easily accessible to plug in, then plug it in everyday when you get home..

 

[Ashful]

It's not daily use. I use it for hauling firewood, tractors, and yard waste. It gets used a half dozen times per year, but often that means several consecutive weekends followed by several months of just sitting. I don't have AC power available where I park the trailer (closest is 70 feet away), so the solar option feels ideal, plug it in and forget it.

Right now, I have 70 feet of cord laid out, to a Battery Tender 0.8 amp maintainer. It works fine, but I read too many stories of fires starting due to extension cords left out long-term, and we do have a lot of animals around who like to chew cords left on the ground.

If I could be sure one of the charge controllers would maintain things properly, I think I'd do best just buying the biggest solar panel available for said controller. I'm not worried about the cost of the solar panel, just want to avoid shortening battery life by excessively over-charging.

Some of these maintainers have automatic scheduled desulfication, and other scheduled tasks aimed at maximizing battery life, if you believe their marketing hype. I've always been told it is best to just leave them plugged in 24/7/365, especially in below-freezing weather, but will admit I'm no expert on battery chemistry.

 

[mellow]

I fully charge the batteries in my camper then push the power shutoff switch so no vampire loads can eat them down, I do this every year and the batteries are OK. The camper sits in storage for about 5-6 months. When I go in the spring to pick it up I have more than enough to power to start the generator to top them off and get going again.

This is for FLA 200ah group 27 batteries.

 

[EatenByLimestone]

10 gauge out to the area and only cry once.

 

[brenndatomu]

We have a system like this at work, except it used to come with the solar panel too...it charges battery's in an outbuilding every day, and has worked very well for us...we've had one solar panel fail, about 8 years in, the new one is still going, been at least another 5 years since the replacement.
Amazon product ASIN B001DZJX6I

 

[Ashful]

10 gauge out to the area and only cry once.

View attachment 318215

I've trenched and buried so much conduit over this past summer that this would be an easy solution, if I only had a good place to pull it from. There's really no practical way to get out of the barn that's 70 feet away, it's on a monolith slab with the electrical feed poured into the slab. I'd have to pull it from the basement of the house, 400 feet away with two driveway crossings and one walkway crossing. Buying new batteries every two years would frankly be easier.

But I don't think it's necessary. The solar solution should be able to work.

 

[Ashful]

We have a system like this at work, except it used to come with the solar panel too...it charges battery's in an outbuilding every day, and has worked very well for us...we've had one solar panel fail, about 8 years in, the new one is still going, been at least another 5 years since the replacement.
Amazon product ASIN B001DZJX6I

Yep. That is exactly the type of system I'm looking at, although I think this one is nicer than the others I've seen. Let me dig into the spec's be sure I can just put a big solar panel on it, and not worry about over-charging.

 

[EatenByLimestone]

A 409 foot run would be a lot more crying. I’d be looking at solar too, lol.

 

[ABMax24]

Solar works good. I've got a 330watt solar panel and a Victron Smart Solar 100/20 solar charge controller on my fifth wheel, it keeps 2 L16's charged all winter. The panel and controller are overkill for battery maintanence, but their primary function is for offgrid camping.

If you get the Victron SmartSolar series that are bluetooth configurable, you can set float, absorption, and bulk charge voltages, and also set equalize voltages, duration, and frequency. This way you can use any solar panel as the input for the controller. They are also temperature compensating and adjust voltages accordingly for temperature (you can set this temperature coefficent as well).

I have my unit setup with 2 charge profiles, one for camping (designed to maximize charging speed at the cost of increased water loss), one for storage for minimal water loss, and lower float voltages to reduce the risk of plate oxidation and sulphation.

Best thing is they are available on Amazon.

 

[Ashful]

Thanks, guys! I'm sold. Will find some time to read up more and make a purchase tomorrow. Today turned out to be real busy.

 

[zrock]

A 100 amp solar panel and controller will do you just fine. That's what i use on my travel trailer and it will bring the battery's up from about 1/2 to fully charged in a afternoon on a good sunny day when im out camping.. So since your trailer is just sitting most of the time this will be more than enough. THey can be had fairly cheap if you look at the sales i picked up my setup for 1/2 price this summer..

 

[Ashful]

I know I'll never average anywhere near the panel rating, maybe not even 10% of it, but I'm wondering why all these systems have such huge panels. Despite being an EE, I don't really work with batteries, so I'm practically a noob when it comes to battery chemistry and application.

Why would anyone want more than a few milliamperes continuous current on a battery for maintenance? Seems most of these panels and chargers are aimed at charging a dead battery, not maintaining an already-charged one over months and years?

 

[EatenByLimestone]

I’ve noticed the older chargers were trickle or lower amp machines while the new ones have a jump start feature. I think I have one that can give a shot of 50 amps or so.

 

[brenndatomu]

Ours at work is a maintainer only...

 

[johneh]

I use a plug-in maintainer 24/7/365
Keeps the batter at full charge and shuts itself off when not needed
Been using it 2 years now without a problem
Amazon

MOTOPOWER MP00207A 12V 2Amp Smart Automatic Battery Charger/Maintainer for Both Lead Acid Batteries and Lithium Ion Batteries​

 

[begreen]

I've been using this maintainer for years on the lawn tractor. Simple and reliable.
Amazon product ASIN B0756Q88J5

 

[Ashful]

I've been using this maintainer for years on the lawn tractor. Simple and reliable.
Amazon product ASIN B0756Q88J5

I have one just like that from Battery Tender, which I also put on my mower in winter, as it sits in a cold shed. Works great, as far as I can tell, I'm on my second battery on a 2007 machine. I have the mating plug wired into the mower, so it's simple plug-and-play at the end of each season.

That little box is presently plugged into my trailer, for the third time in its life, since the solar rig died... again. It seems to work just fine, despite being rated only 0.8 amp output, the charge indicator on my trailer indicates the batteries are holding a good level. Of course, the battery array on my trailer is more like six of those mower batteries!

If I had AC power already run to where the trailer resides, this would be the solution. But right now another solar rig is looking a lot easier than that.

 

[ABMax24]

I know I'll never average anywhere near the panel rating, maybe not even 10% of it, but I'm wondering why all these systems have such huge panels. Despite being an EE, I don't really work with batteries, so I'm practically a noob when it comes to battery chemistry and application.

Why would anyone want more than a few milliamperes continuous current on a battery for maintenance? Seems most of these panels and chargers are aimed at charging a dead battery, not maintaining an already-charged one over months and years?

You charge by voltage, not current, so the output current of the charger only effects how fast you can charge the battery if it's state of charge is less than 100%. A proper charge controller/charger will adjust current accordingly to maintain the set voltage.

Here's a couple charts from Rolls, they're specifically for their batteries, but are going to get you in the ballpark for most deep cycles. Notice the changes in voltages required based on temperature? That's the reason I run a Victron setup in my trailer, my batteries cost almost $1k to replace, a good temperature compensating charge controller is a small fraction of that. By default they just sense ambient temperature at startup every morning, but you can buy an add on sensor that actively monitors better temperature for more precise control. But I've found the internal sensor to be more than sufficient. This is part of the reason many basic chargers or maintainers "fail", because the standard float voltage of 13.5 volts doesn't keep the battery charged in cold weather without temperature compensation and the assumption is the charger is junk when the battery is dead or doesn't start whatever its supposed to start. Or they let them go dead for long enough to sulphate the plates. Conversely, some operate at a higher voltage like 13.8 or 14 volts, which over time boils (really its gases off hydrogen and oxygen by electrolysis) off the water exposing the plates ruining them, or oxidizing the plates when charged at elevated (summer) temperatures.

 

[ABMax24]

I realized I never answered the other part of your question. Large panels are used for 2 reasons:
1. Cost, a 100 watt panel costs only a small amount more than a 25 watt panel, and a 300 or 400 watt residential panel only a little more than that. There can be advantages of a bigger panel, my 330watt panel manages to put a handful of watts into the battery even with 1-2 inches of snow on it. In hindsight I would have went 400watt or 450 watt, as it sure would have helped charge performance on cloudy days, but also a different use case than yours.
2. Voltages, the panel needs to produce a higher voltage than the battery, and if a controller is used (which one should be used), you need a minimum number of cells to produce that voltage. Most controllers need in the 16-24 volt input range before they start sending power to the battery.

 

[mellow]

Wow, another Rolls person, we are a rare bunch I love their FLA batteries for my camper, they have quite a few good videos on youtube.

 

[zrock]

I realized I never answered the other part of your question. Large panels are used for 2 reasons:
1. Cost, a 100 watt panel costs only a small amount more than a 25 watt panel, and a 300 or 400 watt residential panel only a little more than that. There can be advantages of a bigger panel, my 330watt panel manages to put a handful of watts into the battery even with 1-2 inches of snow on it. In hindsight I would have went 400watt or 450 watt, as it sure would have helped charge performance on cloudy days, but also a different use case than yours.
2. Voltages, the panel needs to produce a higher voltage than the battery, and if a controller is used (which one should be used), you need a minimum number of cells to produce that voltage. Most controllers need in the 16-24 volt input range before they start sending power to the battery.

Don't forget that panel output is rated at optimal conditions. So unless you have 100% sun all the time then you will never get the full output..

 

[Ashful]

Thanks everyone, esp. ABMax24.

It looks like all of the Victron MPPT solar products are IP22, which sure is a weird choice for something whose main applications are boats, RV's, trailers... all things that are operated or stored in wet environments. I suppose I can mount it in a project box to keep it dry, as long as I provide some thermal path out to keep the thing from overheating, or choose a different brand that's at least IP67.

What model and panel would you choose for maintaining a pair of 100Ah deep cycles at 12V parallel?