Solar panel charging Lead Acid Batteries

jon641 · Veteran Member

Solar panel charging Lead Acid Batteries

Plendo · Guru

John, lead acid batteries can take a fast charge only so far, then they need to be trickle charged to achieve a full charge. If you assume that you will use power each night, it is unlikely that there would be enough time in a single day for the battery to reach full charge.

Baz421 · Guru

jon641 wrote:
Is it true that the solar panel will only charge lead acid deep cycle house batteries to a maximum of approx 80%, as against gel batteries that will fully charge ?

jon

even an alternator will only charge to about 80% due to battery design/materials. The experts can explain, BUT in practice my 120w solar panel charges an N70ZZ lead acid quite well. I use my old engine starting batteries as aux for fridge and winch, and put a new one on the engine each time - maximises my batteries.

I previously used a deep cycle as aux but was disappointed with cost/reward id you get my drift.

Baz

PeterD · Guru

If you have sufficient panels and your solar regulator switches to its float mode then you will have charged your batteries to at least 95%. All multi stage chargers (mains, DC-DC or solar) operate in a similar manner. The only way solar will not fully charge your battery is if you are short on panels, add more if you are not getting full charge.

jon641 · Veteran Member

Thanks for the replies guys, I have a good 100 amp deep cycle lead acid that will possibly only charge to 80% with the 120 watt solar panel, my dilemma is do I buy another 100 amp lead acid that will then give me 200 amps albeit 80% of it, or scrap the lead acids and buy one 120 amp gel at nearly double the price and have 120 amps available which should recharge back up to full voltage?. I also have a generator capable of charging the batteries if there is no sun.

Stratman77 · Senior Member

I have posted this before, and I believe it is worth reading. The report looks at all types of batteries and their suitability in an RV environment and charging requirements.

Check it out if your'e interested at: www.aandncaravanservices.co.uk/battery-technology.php

Peter_n_Margaret · Guru

jon641 wrote:
Is it true that the solar panel will only charge lead acid deep cycle house batteries to a maximum of approx 80%, as against gel batteries that will fully charge ?

No it is not true.

Provided you can put in more than you are taking out, the solar controller will ensure that the battery becomes fully charged.

How long it takes to achieve full charge is determined by the voltage (determined by the solar controller) and the amps available.

It is essential that the solar controller is providing the appropriate voltages for the particular battery at its current state of charge.

A 20W solar panel offering 17V to a battery with no regulator will overcharge that battery.

1. Ensure that you have good quality solar controller that can be programmed for your battery type.

2. Ensure you have sufficient solar panels to meet your power requirements (as Peter D says).

3. Adding more batteries before the above is done is a waste of money.

Cheers,

Peter

oldtrack123 · Guru

jon641 wrote:
Thanks for the replies guys, I have a good 100 amp deep cycle lead acid that will possibly only charge to 80% with the 120 watt solar panel, my dilemma is do I buy another 100 amp lead acid that will then give me 200 amps albeit 80% of it, or scrap the lead acids and buy one 120 amp gel at nearly double the price and have 120 amps available which should recharge back up to full voltage?. I also have a generator capable of charging the batteries if there is no sun.

HI Jon

As others have indicated, absolutely NO point in adding more batterries[ no matter what type] ,if you are using more power than the solar panels are putting out.

If the loads exceed the panel output, there will be none left over to charge the battery

A good solar/ battery system should be designed based on daily [24h ]power requirements ,then add a factor for bad days with little sun.

Or one can suck it & see smile

A good solar reg with sufficient panel wattage will fully charge your batteries ,or that close that it hardly matters

Re the generator , be careful if you use the 12V output direct to the battery for charging

Most are not regulated & can over charge the battery & realy only have a low 12V Amps output,take hrs to charge

Best to use the 240V connected direct to a good charger smile

PeterQ

-- Edited by oldtrack123 on Friday 5th of December 2014 12:55:47 PM

jon641 · Veteran Member

Thanks everyone for the advice, the only thing running off the Battery during the day would be the 40lt Waeco, I have a 120 watt panel with a direct feed to the 20 amp controller mounted next to the battery, at night I run a couple led strip lights and a tv and sat box, usually unplug the fridge overnight, (it stays cold and I only use it for the drinks) and I plug it back in during the day.

Reed · Senior Member

Apropros of nothing - just wanted to comment that I love the photo that Stratman77 has as atavar. Now that is truly retro.

If you are going to use a generator and solar, use the generator first in the morning and let the solar finish the charge. You can run a generator forever and not see much of a SOC (status of charge) above 90%.

Reed and Elaine

SnowT · Guru

As a Few People above had said...

If your current Battery is not good enough to cover your daily usage the Best bet is to go for More solar Panels over the extra Battery...

- By buying an extra Battery without the ability to charge it is a false economy.. it might work well for the short term but if you fail to fully recharge the batteries then the batteries will die a Quicker death....

--- A well balanced system will have enough solar to Recharge the Batteries to full capacity... and that should be in what is the worst of conditions..

to me an ideal system should not fall below 85% in a single day..

ie if I used 20ah of power over night and had the solar to cover that load and recharge at the same time I would be happy.. the reason I say 15% of capacity is that I like to allow for at least 3days of no sun/solar...

Where a few people fall over is not having the ability to recharge the batteries.. NOT enough solar..

If you run a portable fridge or 2, some led light's and charger's... A single 120w Panel is not going to do the job....
Your aim is to hit over the dreaded 80% state of charge and get as high as you can...

so I don't care of what other say.. A Good solar system will fully charge the system no matter what the load is....

Juergen

My own system, even thou I don't have Lead Acids.. I use the extra power to do thing's like run my Hot water system..

-- Edited by SnowT on Friday 5th of December 2014 08:20:16 PM

Stratman77 · Senior Member

As a relative newbie, I relish all the great tips, etc. from all you experienced campers out there! Initially, I wasn't sure of my exact needs during a prolonged freecamp, and accept that my 120watt solar would struggle with the car fridge on 24/7 and at night the TV, media player, fan (when hot) and CPAP (wife) machine and some lights (soon to be LEDs). So I chickened out and bought a genny that will run the whole flamin' van including A/C as SWMBO just can't handle hot weather - especially hot nights! Fortunately, I haven't needed it yet, but I'm sure the time will come. Oh. And thanks for the nice words about the old van photo, Reed. Retro really doesn't cover it!

exa41 · Guru

Hi John , well I have just gone through the exercise , at greens last week we found that a cloudy day limited our system greatly , we have a 12v fridge a 12v freezer tv lights etc etc and ran low ( not too low) on power during the night . I had 240 watts solar and 200 ah batteries , my battery man said as others have said above that extra batteries would not help so I added another panel of 140 watts and at the moment they are pumping 15v with 98% charge , looks like we wont be back to Greens until Monday but that will then test the system again. The trick is a good MPPT solar controller and go up one size in cable to prevent voltage drop, I also fitted a 12/12 DC charged , hope it works.

PeterD · Guru

jon641 wrote:
1. Thanks for the replies guys, I have a good 100 amp deep cycle lead acid that will possibly only charge to 80% with the 120 watt solar panel,
2. my dilemma is do I buy another 100 amp lead acid that will then give me 200 amps albeit 80% of it,
3. or scrap the lead acids and buy one 120 amp gel at nearly double the price and have 120 amps available which should recharge back up to full voltage?
4. I also have a generator capable of charging the batteries if there is no sun.

1. On what basis are you basing this 80% maximum charge? It's a possibility your are misinterpreting your readings. There is another possible source of your problem, the regulator may not be set correctly or faulty. Are you at any time seeing the regulator go into its float mode?

2. If you install a 200 Ah bank of batteries without an increase in your solar panel capacity you are likely to only charge the batteries to 40% over a long period without any mains charging or charging your batteries from the tug. If your solar regulator is doing its job properly you have insufficient solar capacity (or you are misinterpreting the battery capacity.)

3. GEL batteries are just another type of lead acid battery. The main difference is the electrolyte used in the construction. You will achieve little for a hell of a spending spree.

4. What ever you do with your solar/battery system don't throw it away. You may still need it some day in atrocious weather conditions.

moblet · Senior Member

A 120W panel and 100Ah battery is theoretically capable of keeping up with your stated power demand. I ran a 31L Waeco 24/7 long-term at 4 degrees C from a 40W portable panel. With a battery of that size there should be no need to unplug the fridge unless the battery isn't adequately charged by sunset.

It sounds to me like you have no method of tracking your battery's state of charge (SoC), and without this information you're very much in the dark about the day-to-day performance of your system and any money you spend may be wasted. I bought an LED meter that plugs into an accessory socket, which gives me a quick and convenient reading of the battery voltage. Another source of information is your solar charge controller - even basic controllers usually have an LED that indicates when the battery has reached "float charge" status, meaning it is has effectively reached full charge, along with an indicator if the SoC is getting low. If your controller gives you this information have a look at it occasionally through the day to see if it's reaching float. If your battery is never reaching float charge then your panels aren't meeting your demand, but if it reaches float charge most days then your panels are keeping up.

jon641 · Veteran Member

Thanks everyone, the "float charge indicator is a new one to me, I do have 3 lights on the controller but have only ever see 2 light up, so will def have a look at that before we head off again>

moblet · Senior Member

If you can't find the instructions for your controller tell us or link us to the model and we can likely tell you what to look for. (Most of the smaller controllers I've seen have a green LED that lights when the panels are pumping, and a multi-colour LED for the battery condition. It'll be green when the SoC is adequate, and orange or red when it isn't. During float charging the green LED will flash slowly.)

Jaahn · Guru

Stratman77 wrote:
I have posted this before, and I believe it is worth reading. The report looks at all types of batteries and their suitability in an RV environment and charging requirements.

Check it out if your'e interested at: www.aandncaravanservices.co.uk/battery-technology.php

Hi Stratman77,

I had a look at that site. Interesting to see another point of view. smile However some statements seemed a bit sus;

"If your Motorhome has a sophisticated charger controller like a ---- it will prevent any more power being taken from the battery once it drops below 11v to prevent battery damage. So if you have spent £700 on a battery that will safely Deep Discharge down to 8v, you will have wasted your money."

Hmmmmm 8 volts disbelief that's some remarkable battery !

Jaahn

oldtrack123 · Guru

Jaahn wrote:
Stratman77 wrote:
I have posted this before, and I believe it is worth reading. The report looks at all types of batteries and their suitability in an RV environment and charging requirements.

Check it out if your'e interested at: www.aandncaravanservices.co.uk/battery-technology.php
Hi Stratman77,
I had a look at that site. Interesting to see another point of view. However some statements seemed a bit sus;
"If your Motorhome has a sophisticated charger controller like a ---- it will prevent any more power being taken from the battery once it drops below 11v to prevent battery damage. So if you have spent £700 on a battery that will safely Deep Discharge down to 8v, you will have wasted your money."
Hmmmmm 8 volts that's some remarkable battery !
Jaahn

Hi Jaahn

Apart from the 8V ,even taking LA batteries down to 11 volts could be bad for them[particularly if that is with a light load ]

11V is near dead flat[ actually around 95% discharged]

PeterQ

-- Edited by oldtrack123 on Sunday 7th of December 2014 03:16:34 PM

Jaahn · Guru

oldtrack123 wrote:

Hi Jaahn
Apart from the 8V ,even taking LA batteries down to 11 volts could be bad for them[particularly if that is with a light load ]
11V is near dead flat[ actually around 95% discharged]

PeterQ
Yea can't argue with that. Perhaps those guys are expert at chargers for batteries, but not so good on discharging batteries.
As we know voltage, when discharging is a very variable thing and needs a book to qualify it to an actual figure. If all you have is a voltmeter or a row of leds then you probably should be cautious discharging to lowish voltages.
Jaahn