Affordable Charge Controller for AGM Battery

[photolimo]

I am experimenting with solar for the first time trying to get my head around the concept by testing out cheap components. I received an AGM battery for a bargain from a local golf cart shop that is a 12V 212Ah SunXtender. I am planning to charge it with a 100W poly panel and a PWM charge controller. What I found is that the voltages are slightly off for what is recommended for my AGM.

Charge: 14.4V recommended vs. 14.6 given.
Float: 13.4V recommended vs. 13.6V given.

Is this a problem? Should I seek out another charge controller? If so what would you recommend under ~$50.

[SunEagle]

I am experimenting with solar for the first time trying to get my head around the concept by testing out cheap components. I received an AGM battery for a bargain from a local golf cart shop that is a 12V 212Ah SunXtender. I am planning to charge it with a 100W poly panel and a PWM charge controller. What I found is that the voltages are slightly off for what is recommended for my AGM.

Charge: 14.4V recommended vs. 14.6 given.
Float: 13.4V recommended vs. 13.6V given.

Is this a problem? Should I seek out another charge controller? If so what would you recommend under ~$50.

The CC is a PWM type which means it is "amps in = amps out". So whatever that 100 watt panel Imp is rated (~5.5amps) is what you will be charging your 212Ah battery. That calculates to C/38 which is way to slow to properly charge your battery. If you use the PWM CC you will need about 400 watts of panel which can get you a C/11 charge rate. Or get a 30amp MPPT type charger (watts in = watts out) and a 250 watt panel will get you a charger rate ~ C/10 which is ok for that battery.

[photolimo]

The CC is a PWM type which means it is "amps in = amps out". So whatever that 100 watt panel Imp is rated (~5.5amps) is what you will be charging your 212Ah battery. That calculates to C/38 which is way to slow to properly charge your battery. If you use the PWM CC you will need about 400 watts of panel which can get you a C/11 charge rate. Or get a 30amp MPPT type charger (watts in = watts out) and a 250 watt panel will get you a charger rate ~ C/10 which is ok for that battery.

The rate of charge is not something I had considered before, thanks for pointing that out.

I looked up some info on this to clarify what you were describing. C/10 means: "a charge rate in amps of one-tenth the overall battery capacity in amp-hours" Correct?

Target: 212Ah/10 = 21.2Amps or 21.2Amps/212Ah = 0.1C
Current: 212Ah/5.5Amps = 38C or 5.5Amps/212Ah = 0.026C

[photolimo]

The CC is a PWM type which means it is "amps in = amps out". So whatever that 100 watt panel Imp is rated (~5.5amps) is what you will be charging your 212Ah battery. That calculates to C/38 which is way to slow to properly charge your battery. If you use the PWM CC you will need about 400 watts of panel which can get you a C/11 charge rate. Or get a 30amp MPPT type charger (watts in = watts out) and a 250 watt panel will get you a charger rate ~ C/10 which is ok for that battery.

SunXtender Technical Manual: "For repetitive deep cyclying applications (deeper than 50% DOD), chargers should have a current of at least 0.2C. If a charger with at least 0.2C is not practical, an alternative charge profile using a low rate constant current stage at the end of the absorption stage will normally improve the life cycle. The constant current stage should be at 0.02C for no more than one hour."

Recommended Standard Charge: 210Ah*2/10 = 42.4Amps
Recommended Low Rate Charge: 210Ah*2/100 = 4.24Amps

I am not sure what this low rate charging would look like or what kind of device would do that. Any ideas?

[SunEagle]

SunXtender Technical Manual: "For repetitive deep cyclying applications (deeper than 50% DOD), chargers should have a current of at least 0.2C. If a charger with at least 0.2C is not practical, an alternative charge profile using a low rate constant current stage at the end of the absorption stage will normally improve the life cycle. The constant current stage should be at 0.02C for no more than one hour."

Recommended Standard Charge: 210Ah*2/10 = 42.4Amps
Recommended Low Rate Charge: 210Ah*2/100 = 4.24Amps

I am not sure what this low rate charging would look like or what kind of device would do that. Any ideas?

AGM type batteries allow you to be more aggressive when charging. So a C/5 or 42.4amps for a 210Ah battery is acceptable.

The Low Rate Charge is nothing more than a "Float" charge cycle which is there to get the last few % of the battery up to 100. Quality charge controllers have at least 3 stages of charge with the "Float" being the last and using the lowest amount of amperage.

Normally you have run out of useful sun to complete the 100% charge if you discharge the battery too much.

[Sunking]

I looked up some info on this to clarify what you were describing. C/10 means: "a charge rate in amps of one-tenth the overall battery capacity in amp-hours" Correct?

Almost correct, it means the 10 Hour Rate. C = the battery AH CAPACITY, and x = Hours.

Amps = AH/H

So for a 212 AH battery C/10 = 212 AH / 10H = 21.2 Amps

It can also be expressed as a number like .1C so .1 x 212 = 21.2 amps.

However don't get to caught up in any of this. In any off-grid solar design using batteries there are two critical factors in making sure the system will do what it is designed to do.

1. There must be enough panel wattage to replace all the energy used in a day under worse case conditions. Otherwise you would be a Democrat battery charger operating at a DEFICIT CHARGING which means you destroy the battery in short time, go dark, and blame someone else for your ignorance and expect a bailout.

2. After requirements of #1 are met you must make a sanity check to be sure the panel wattage is within the minimum/maximum charge rate requirements of the battery. As a general rule for Flooded Lead Acid battery min = C/12 and max = C/8. For AGM is more forging of a max of C/4 and no real minimum because stratification is not an issue with them.

Having said that in your location is a bit unusual being in Sun Valley AZ with way above average Sun Hours your panel wattage will be too small to support FLA batteries forcing you to oversize panel wattage. Real life example if you want say 1 Kwh per day requires a 5 Kwh battery. If you were to select a 12 volt battery would need a 400 AH battery. Using a MPPT controller and December Sun Hours of 5 Sun hours means you only need a 300 watt solar panel. Well a FLA 400 AH battery requires a minimum 400 AH / 12 H = 33 Amps of charge current and a 300 watt panel on a MPPT will only generate 25 amps. So you would need a minimum 400 watt panel.

Now you could use a AGM battery and that would solve the problem, but not a wise financial decision. Adding 100 watts of solar panel only adds $80 to $120. But to use AGM in place of FLA is going to hurt. A 400 FLA good quality 5 year battery is going to cost you roughly $700 to $900. A pair of Sun Extender PVX4050HT is going to cost you just over $1400 and only last half as long as FLA batteries. So when you look at short term initial cost AGM is roughly 100% higher and long term is 200% higher in cost.

Having said that does not mean to never use AGM as it has its applications.

[photolimo]

Thanks for the responses. I am aware that AGM is not always a smart financial choice but since I sourced mine used for less cost than a used FLA battery that is what I went with. I appreciated the advice and thought process though.

I know my panel is less that what would be desired in a full reliance situation but I am just experimenting with solar for some hobby projects and trying to size my usage based on the panel I have.

I just want to make sure that the slow charge rate and voltage won't kill the battery.

[russ]

Thanks for the responses. I am aware that AGM is not always a smart financial choice but since I sourced mine used for less cost than a FLA battery that is what I went with. I appreciated the advice and thought process though.

I know my panel is less that what would be desired in a full reliance situation but I am just experimenting with solar for some hobby projects and trying to size my usage based on the panel I have.

I just want to make sure that the slow charge rate and voltage won't kill the battery.

Got what it was worth?

[Sunking]

Charge: 14.4V recommended vs. 14.6 given.
Float: 13.4V recommended vs. 13.6V given.

With a 100 watt panel, 5 amp of charge current (C/44), no problem. A 100 watt panel on that battery is a Trickle Charger, not a charger

You should be more worried about undercharging the battery, not over charging.

[photolimo]

Got what it was worth?

What are you referring to?

[photolimo]

Thanks for the responses. I am aware that AGM is not always a smart financial choice but since I sourced mine used for less cost than a FLA battery that is what I went with. I appreciated the advice and thought process though.

I know my panel is less that what would be desired in a full reliance situation but I am just experimenting with solar for some hobby projects and trying to size my usage based on the panel I have.

I just want to make sure that the slow charge rate and voltage won't kill the battery.

Found this kit for $100.

Also found these controllers. They will sell a sample for $100 but they go for $45/1000.

[Sunking]

Don't go spending any money yet because you have some issues to resolve.

1. Your battery is used. Concord makes fantastic AGM batteries, but it is a AGM battery and at best 2 to 4 years service life. If you bought them from a golf course they have already been in a gold cart for at least 2 years and got replaced because they are getting weak.

2. You only have a 100 watt panel which severely limits what you can do. If you have a PWM controller, the largest battery it can support is 50 AH. If you have a top of the line MPPT controller can support up to 100 AH battery. Either way is not much and at best will only reliably run a laptop and charge up cell phones.

You basically have a toy. To generate any meaningful power you are looking at $3000 to provide you with 10-cents of electricity per day with a 300 pound $1000 battery.

[Amy@altE]

An important question hasn't been asked. How much power will you be using a day? All of the discussions have been assuming using 50% of the battery a day. If you are only using a small fraction of the battery capacity, you don't need to refill that much, just what you used.

I recommend a Morningstar SunSaver SS-10-12V. It does 3 stage charging, has a jumper to select flooded vs AGM, and costs under $50.

[SunEagle]

An important question hasn't been asked. How much power will you be using a day? All of the discussions have been assuming using 50% of the battery a day. If you are only using a small fraction of the battery capacity, you don't need to refill that much, just what you used.

I recommend a Morningstar SunSaver SS-10-12V. It does 3 stage charging, has a jumper to select flooded vs AGM, and costs under $50.

Amy

I believe the OP is wanting to "experiment" with solar and batteries and really does not have a good understanding of what his "daily load" will be.

This is a repeat of many people who first come into the forum after they have gotten "free" panels or batteries and now want to learn what type of CC they need to get and why can't they find a "cheap" one since they just want to experiment.

It is an example of someone having high hopes for solar and little understanding of the true cost to build a good and balanced system. Hopefully they learn before the waste a lot of money on hardware that is useless.

[photolimo]

An important question hasn't been asked. How much power will you be using a day? All of the discussions have been assuming using 50% of the battery a day. If you are only using a small fraction of the battery capacity, you don't need to refill that much, just what you used.

I recommend a Morningstar SunSaver SS-10-12V. It does 3 stage charging, has a jumper to select flooded vs AGM, and costs under $50.

I have a 50w DC light that I am looking to power for 12 hours a day. It has a voltage regulator on it to help manage the power consumption/brightness. I am hoping to fine tune the battery/panel power this way.

Thanks for the recommendation.