Solar Trickle Charger for House AGM Battery

[SCMatthew]

Hello all,
I've got a dying Lifeline 4D that I believe ran down too many times. I was wondering instead of going full solar if I could plug one of the solar trickle chargers into the 12V outlet.
I did a search and didn't find anything. If you are aware of a post, please point me in the right direction.
Also, thinking about installing a battery cutoff switch to stop the propane and CO2 detectors from drawing down the new battery.
Any help would be appreciated.
Matt

[posplayr]

Figure the minimum charge rate is C/10 where C is the amp hour rating of your battery setup.

So if you have 100 amp hours you need to charge at 10 amps to charge.

In simple math (easy to remember): 10 hours X 10 amps/hour is 100 amp hours to get fully charged.

Trickle chargers often 1-2 amp limitations so they will not charge a 100 amp hour battery any time soon.

[boywonder]

Originally Posted by posplayr

Figure the minimum charge rate is C/10 where C is the amp hour rating of your battery setup.

So if you have 100 amp hours you need to charge at 10 amps to charge.

In simple math (easy to remember): 10 hours X 10 amps/hour is 100 amp hours to get fully charged.

Trickle chargers often 1-2 amp limitations so they will not charge a 100 amp hour battery any time soon.

Posplayr: Where are you getting the C/10 rule???? If this held true many of us here would never get our 350aH batteries fully charged with our 300W of solar.....


I've never seen anything close to 35A of solar even on a cold day with the sun directly overhead.



If there is no drain on the battery (OP is considering a switch to disable CO/propane detectors) then a 1 amp charger will fully charge a fully discharged 100aH battery in 100 hours...neglecting the tiny self-discharge rate of the battery...more or less....

[posplayr]

Originally Posted by boywonder

Posplayr: Where are you getting the C/10 rule???? If this held true many of us here would never get our 350aH batteries fully charged with our 300W of solar.....


I've never seen anything close to 35A of solar even on a cold day with the sun directly overhead.



If there is no drain on the battery (OP is considering a switch to disable CO/propane detectors) then a 1 amp charger will fully charge a fully discharged 100aH battery in 100 hours...neglecting the tiny self-discharge rate of the battery...more or less....

boywonder

Normalized charging rate, C, is a very common parameter used for assessing battery charging rates.

https://batteryuniversity.com/learn/...2030%20minutes.

I annotated the first figure from this reference on Lead Acid batteries. You can see why most all cars have a voltage regulator/alternator set to 14.5V. This is the voltage you need for 93-95% SOC at C/10. Basically, it means that you can drive your car for relatively many hours at that voltage without overcharging your batteries.

http://www.scubaengineer.com/documen...ing_graphs.pdf

Recall for a typical off-grid solar application, you never run batteries to 0% SOC. For LA you typically never go below 50% with 75% recommended.

For discussion assume a typical daytime solar hour is 10 hours per day. 350 A-hr AL would require nominally 175 A-Hr and 87.5 A-hr for 50% and 75% SOC respectively. Properly sized you would need charging rates for 17.5 amps and 8.8 amps respectively.

These correspond to 17.5/350= .05C and 8.8/350=.025C respectively. Basically, you can see that the typical solar system is "underpowered" compared to car's charging system. A car battery with a deep cycle aux might be 125 amp Hrs at most with a 135 amp rated alternator you would be at 1C if most all of the power was available to the charging system. It might be closer to 0.5C but well above what the solar systems need to do.

As far as OP's situation. I don't know what the objective is. The objects (as you describe) seem to be to maintain a charge against a 1 amp load? 1 amp load at 12.8V is about 15 watts assuming some losses. Considering the OP feels he killed his battery because of running it too low too many times, I'm not sure what 15W of charging is going to do in this situation.

1/125 = .008C

4% per week is quoted from below corresponding to 5 amp-hours per week. So if you are looking at a "storage solution", the 1 amp charger will take care of self-discharge but I don't think that is an accurate appraisal of OP's usage. At least it does not appear to be what is killing his old batteries.

All batteries, regardless of their chemistry, will self-discharge. The rate of self-discharge for lead acid batteries depends on the storage or operating temperature. At a temperature of 80 degrees F. a lead acid battery will self-discharge at a rate of approximately 4% a week. A battery with a 125-amp hour rating would self-discharge at a rate of approximately five amps per week. Keeping this in mind if a 125 AH battery is stored for four months (16 weeks) winter without being charged, it will loose 80 amps of its 125-amp capacity. It will also have severe sulfation, which causes additional loss of capacity. Keep your batteries charged while not in use!

https://www.progressivedyn.com/servi...s%20per%20week.

[posplayr]

If you want any hope of this working for storage (i.e. 1 amp draw), you are probably going to need something like this. It is rated at 30W which considering that is a solar number might get you 15W in actual practice for 10 hours per day (average). But remember this is only 10 out of 24 hours in the day. So you are back down to 40% of what you need again. This is just assuming a constant 1 amp draw (day and night)

All the other panels I saw are typically 10 watts max.


https://www.amazon.com/dp/B07XY1CV5F...jaz10cnVl&th=1

See this review LOL

David handyman
5.0 out of 5 stars works as described
Reviewed in the United States on February 28, 2021
Size: BC-30W PolyVerified purchase
So excited with this unit, while only 30 W it does a great job at topping off my coach batteries. My prewired RV system will take up to 100 watts so wondering if I can string 3 of theses together.

Update since purchase STILL WORKS GREAT Only wish I had purchased the 100 W panel

1 amp is a lot of parasitic draw; might I suggest a power shut-off main fuse. I use these.

https://www.amazon.com/-/es/gp/produ...?ie=UTF8&psc=1

[BCam]

Amazon has quite a few, here's one example:

https://www.amazon.com/Sunway-Solar-...NsaWNrPXRydWU=

However, I think you'll be much happier with 20W - 50W, hard-wired. Here's a link to a reasonably priced ($49.99) 20W kit that includes a controller for not much more money:

https://www.amazon.com/TP-solar-Mono...0301636&sr=8-4

And a 50W kit for $89.99:

https://www.amazon.com/SOLPERK-Monoc...0302108&sr=8-3

I have an old 50W panel temporarily mounted to my motorhome's rear ladder that does a great job keeping both my house and starting batteries topped off while in storage. I have an Amp-L-Start installed between my house batteries and my starting battery. Before it failed, my 19 year old 15W OEM panel kept things charged as well but wasn't as nearly as efficient.

Think of the above options as maintainers only. They don't have enough wattage to recharge your batteries after use in any reasonable amount of time.

I have 320W of solar panels waiting to be installed on my MH at a later date. I have a 100W panel on my E350 and a second awaiting either installation or modification as a DIY portable panel.

None of the above will obviate the need for a new battery but will keep your new battery healthy.

Is your house battery set up to charge off your alternator? If not, this would help as well.

[1der]

What is the thinking behind the the "10 hours per Solar Day"? Typical is around 3 to 6 effective hours per day for solar calculations depending on latitude and time of year.

https://www.solardirect.com/archives...sun-hours.html

[boywonder]

Posplayr: Your C/10 charge rate assumes that you'd like to fully charge a fully depleted battery bank in 10 hours.......I'm assuming that's where C/10 is coming from......


Clearly there is no argument that your average 125A alternator is up to that task (although I have noticed that I get maybe a max of 40A or so getting to my house batteries even when they are down to say 70% SOC while driving).


I'm not sure many folks here are expecting even a fairly sizable RV solar system to fully charge a depleted house battery bank in 10 hours, that's not really do-able for most of us.....and as 1der mentioned above unless you can point your panel at the sun all day you just aren't gonna get there.


Even at the recommend 50% minimum SOC for lead acid chemistries it can be challenging to get enough sun on roof mounted panels in a day for most van sized systems although it's quite achievable on paper.


For easy math 240aH battery * 50% SOC=120aH.....240W of panels yields 20 amps in the lab but more like 14A or so in real life....so if you can get 8+ hours of "lots of sun" you may get there.....


I believe that the OP was simply asking if a 1 amp trickle charger will keep his battery topped off sitting in his garage/driveway if he turns off his typical parasitic draw items like CO detector.....not sure he's expecting to top off a fully discharged battery in 10 hours......

[posplayr]

Originally Posted by 1der

What is the thinking behind the the "10 hours per Solar Day"? Typical is around 3 to 6 effective hours per day for solar calculations depending on latitude and time of year.

https://www.solardirect.com/archives...sun-hours.html

10 is a peak number for "Kilowatt-hours per square meter". These are daily numbers and in the summer in the Southwest US, you can get to 10, but generally less than that in other areas. I picked 10 to make the math easy; adjust according to your region.

So you are correct; generally the number is less than 10 hours.

https://www.solar-electric.com/learn...ion-maps.html/

kilowatt-hours per square meter: The earth at sea level receives about 1,000 Watts per square meter. If the map says 9 kWh/m2, then you are getting about 9 full hours of sunlight on the panel. Modern solar panels are around 15% efficient, so that works out to approximately 150 watts per square meter, or 15 watts per square foot.

[posplayr]

Originally Posted by boywonder

Posplayr: Your C/10 charge rate assumes that you'd like to fully charge a fully depleted battery bank in 10 hours.......I'm assuming that's where C/10 is coming from...... ......

Well you can assume what you want but that is not where C/10 comes from. It is a generally accepted charging rate that can be used for extended periods or safely charge almost any battery type overnight. In the specific case for LA batteries, it relates to the 14.5v alternator set points. Again you can run your vehicle down the road till you need to refill and at 14.5V you will not in any way damage the LA battery.

Originally Posted by boywonder

Clearly there is no argument that your average 125A alternator is up to that task (although I have noticed that I get maybe a max of 40A or so getting to my house batteries even when they are down to say 70% SOC while driving).

......

I was pointing out that an alternator can charge much higher than C/10 but as SOC approaches 100% that charge rate will tend toward C/10 due to the 14.5V set point.

Originally Posted by boywonder

I believe that the OP was simply asking if a 1 amp trickle charger will keep his battery topped off sitting in his garage/driveway if he turns off his typical parasitic draw items like CO detector.....not sure he's expecting to top off a fully discharged battery in 10 hours......

I think the question has been answered with about 3 data points. If you are using a 1 amp trickle charger running of 120V, then it will replace a 1 amp continuous load. Depending upon battery size and SOC OP can calculate how long any excess capacity that trickle charge will take to recharge a dead battery.

However, the question seems to be focused on "Solar trickle Charging" . Now it takes in the best case 1*13.0*1.15*24/10= 36 watts with 10 sun hours.

(1 amp, 13V, 85% conversion/charge efficiency)

Derate that 10 solar hours to only 6 hours and you have 35*10/6= 60 watts required. If you don't get full sun, then double it again 120 Watts. That is a daily common suggestion in solar sizing.

Make any required adjustments, but you are going to need a fairly large panel to deal with a full amp of the draw. I'm ignoring the cut-off switch for the CO detector because I don't know how much of the 1 amp that is.

I have a Safety-Alert for propane and I think it is about 25 mAmp.

Bottom line, a 1 amp load is a fairly high drain (like having an incandescent dome light on continuously) even without having your battery discharged. I would try and address lower this and then a simple dashboard solar charger will work to handle the batteries "self-discharge rates"