Adding batteries to 24V system

[Draddog2169]

I am now running a 24v system by using 4 - 6v flooded batteries. I don’t have enough battery to take several showers. I run a deep well pump with the system. The pump draws 9.6 amps when running and 19 amps on start up. I would like to add more batteries. I was looking at adding 2 more 6v batteries in series, but that is only 12v. The 2 new batteries would be placed in parallel with the 24v batterie. Can this be done or do I need to add 4 batteries that equal 24 volts. Jerry

 

[Q-Dog]

No, you cannot parallel 12 volt and 24 volt batteries.

 

[Draddog2169]

I am now running a 24v system by using 4 - 6v flooded batteries. I don’t have enough battery to take several showers. I run a deep well pump with the system. The pump draws 9.6 amps when running and 19 amps on start up. I would like to add more batteries. I was looking at adding 2 more 6v batteries in series, but that is only 12v. The 2 new batteries would be placed in parallel with the 24v batterie. Can this be done or do I need to add 4 batteries that equal 24 volts. Jerry

No, you cannot parallel 12 volt and 24 volt batteries.

So do I need to get 4 more batteries so I have 2 strings at 24 volts

 

[SupraSPL]

I have separate 24V and 12V banks. I use the 12V bank to run RV pumps, hard drives, modems, leds, drone battery chargers etc. And of course to run 12V inverters. The 24V bank I use for 24V inverters, power tool and power station battery chargers.

The downside is you need a separate solar string and MPPT to charge each bank. Also it is 2 banks to keep an eye on to make sure they arent running low or overflowing.

 

[MichaelK]

How old are your first set of batteries? What generally happens with parallel strings is that the reduced capacity of the older set drags down the capacity of the new set. Since you are using this bank to power your on-demand water heater, and a well-pump, I'll guess that they have been severely drained several times by now.

You have a couple of choices here for you. What you can try first is getting set #1 fully charged, and equilized, and then check the specific gravity of the set #1 electrolyte to see how much of the original capacity you still have. If it looks OK, then go head and splice in the second set of four new batteries in parallel. I would continue to monitor and record the SG of both the old and new sets to make use the SG starts to drift down.

Your second option is simply to trade in the old batteries for a larger set, say Trojan L-16s. That will about double your storage capacity.

BTW, are you going to upgrade your solar at the same time? It is NEVER a good idea to upgrade battery capacity without first upgrading the solar. Over the years, there have been countless battery banks destroyed by chronic undercharging. A 200-250Ah golf-cart battery will want to get charged at ~25-30A. An L-16 would like 50A. Assuming you re-rate you panels to 85% for real-world production, that means (50A X 25Vcharging)/85%= 1470W of panels. Call that six 250W residential panels.

 

[Draddog2169]

MichaelK, Thank you for the thought on checking SG on the 4 batteries I have. I didn’t think about that. I currently have 4 - 200 watt panels and adding 2 more 200 watts when I add batteries. That would give me 1200 watts. Looks like I may be short on panel wattage also. I need to say I don’t run a water heater on this system Only well pump. I have a propane tankless water heater for showers. I now know that if I want to add batteries I will need to add 4 more Because I have a 24v system. My current batteries are 3 years old.

 

[MichaelK]

My bad! Mentioning too many showers meant hot water to me.

Three years old is past what I would consider acceptable. I'd say 12 months would be OK. What exactly is the amphour size of your batteries? Are they Trojan T-105s? Let's do the math for your battery assuming the size is 250Ah. If it isn't correct, just plug in your numbers.

[(250Ah/8) X 25Vcharging]/85% = 919W of panels Let's just call that 900 and don't worry about it. So, you were reasonably close to optimum when you implemented 800W of panels. Doubling the battery though means doubling the solar, so even just two extra panels is not enough. With 1840W being optimum, you're only 2/3rds of the way there with 1200W.

 

[Draddog2169]

They are Rolls flooded L16 batteries at 390 ah. I do need to move my solar array. The trees have now grown higher and puts some shade on the array later in the afternoon. I also get some shade from morning sun. I only get about 4 hours of good sun. i am intending to move my solar array next summer. Micheal you sound very knowledgeable on solar calculation. I understand electricity and went to school for it, but not very knowledgeable about solar and its calculation. Thank you for helping me out. More information on my situation. It is a weekend cabin with very low power use when we are there except for the well usage. Two years ago I upgraded the maintenance center from a 50watt to a 3000w. Last summer we added the well pump to the system. Before that we took out the generator and plugged it to the well pump. We can take 2 showers with no problem, but 3 or 4 showers are too much For the 4 batteries. Maybe my issue is besides not enough battery is not enough solar. Da I guess I now realize that. Guess I am short on both ends. When the array is in full sun I only see 15 to 18 amps charging. Should I start with adding more panels first. Maybe I am not charging my batteries to their full potential.

 

[MichaelK]

They are Rolls flooded L16 batteries at 390 ah. I do need to move my solar array. The trees have now grown higher and puts some shade on the array later in the afternoon.

With only four hours of good sun, that should be thrown into the calculation. Maybe scaling your solar to 2X to compensate for getting less than full sun across the day.

Maybe my issue is besides not enough battery is not enough solar. Da I guess I now realize that. Guess I am short on both ends. When the array is in full sun I only see 15 to 18 amps charging. Should I start with adding more panels first. Maybe I am not charging my batteries to their full potential.

Trojan recommends a charging rate of 13%, or 1/8th of C, so doing the math, your 390Ah batteries will want 390Ah X 0.13 = 51amps. To get an honest 51 amps while charging at a minimum of 25V, I like to add a 85% correction factor. That means in real-world conditions, don't expect the panels to put out more than 85% of what their rating says. So, getting back to the math, (51A X 25Vcharging)/85% = 1500W of solar.

With 800W of panels, I would have expected more from your panels. I would have expected to see (800W/25V) X 85% =27A at noon. So, there's a big descrepency between you potentially producing 27A, but only seeing 15-18A? I think this is an issue that should be investigated further? What kind of charge controller do you have? Is it PWM or MPPT? Your numbers look like PWM numbers? There is a problem with fake MPPT controllers on the market. Can you show use some pics of what controller you have?

What needs to be done here is to upgrade your system to the point that your 15-18A of output gets raised to 50+A. Then your batteries will be happier.

 

[Draddog2169]

Here is what I purchased. We felt we needed a 3000W to run the well pump. The well pump at start up draws 19A and running is at 9A. At one time looking at the solar charger screen I thought I saw a 55A draw from the batteries. When I move the panels I should get 6 to 8 hours of sun. As far as other draws from the batteries, we only use lights, tv and radio. No microwave or electric appliance. At this point I am just trying to get the well pump to fit our needs. Oh yes, the well pump is also used to run the kitchen faucet when water is needed. Very low use.

 

[MichaelK]

Are these the specifications for the unit you bought?

The surge rating in the table looks great, though I am a bit skeptical. 9000W for 20 seconds seems like a very long time for an inverter this cheap?

One thing that stands out to me though is the relatively low maximal solar voltage, which is recommended not to exceed 85V. That's really not much if you want to locate your panels a good distance away from the batteries. I myself have 200V Midnights, and I have arrays with four 250W grid-tie panels wired in series for 120VDC. I can send about 8A about 130' with no measurable voltage drop with 10 gauge solar cable. That allows me to position my arrays in the very best locations to get optimal sun the whole day.

If you wanted to optimize location in the same way, it might be valuable for you to buy a separate charge controller, rather than passing the power through the MPPT of the SunGold. You could get something like a Tracer AN 6420, which would allow you to upgrade to 1500W of panels that can be placed anywhere you want, say within 150'.

 

[Draddog2169]

MichaelK, sorry with Christmas and all I got sidetracked. Yes those are the specs of my charge controller. Do you have a larger panel than mine. Mine is only 3000w. I see that this charge controller can handle up to 1400W from the panels. When I move the panel array it would only be 30 feet from the charge controller. Currently it is about 20 feet from the charge controller. Would the tracer replace my current charge controller

 

[Draddog2169]

MichaelK, it looks like the Tracer is a communication piece of equipment that would leave me communicate with my charge controller. Correct.

 

[MichaelK]

Do you have a larger panel than mine. Mine is only 3000w. I see that this charge controller can handle up to 1400W from the panels.

Not sure what this question means? What does "larger panel" refer to? Do you mean the SunGold Power unit? It is appropriate to call it an All-in-One, or AiO, because it incorporates a charge controller, an inverter, and a charger, all in one box.

When I move the panel array it would only be 30 feet from the charge controller. Currently it is about 20 feet from the charge controller.

I have Midnight200 controllers. That lets me run four 30V residential panels in series to get 120VDC. I can run the raw solar power ~125' away without any detectable voltage drop in 10 gauge wire. You could do the same thing with a Tracer 5420 or 6420, which also has a 200V limit. Remember, it's the Voc on the coldest day of the year, not the typical output voltage.

Would the tracer replace my current charge controller

It could work side by side with your AiO. Don't refer to your SunGold as a controller. It has a charge controller built in, but it is more than just a controller. What you would do in this situation is wire the Tracer directly to the batteries, and wire the solar into the Tracer, not using the solar terminals on the SunGold at all. Only the battery to inverter terminals would be connected between the batteries and the SunGold. So, the Solar fuels the Tracer, the Tracer charges the batteries, and the batteries fuel the SunGold. Remember, always connect the battery to the Tracer first, before connecting the solar to the Tracer.

MichaelK, it looks like the Tracer is a communication piece of equipment that would leave me communicate with my charge controller.

The Tracers can be purchaced with the optional MT-50 data unit. You string a wire from the controller itself over to the spot where you want to monitor it, and mount it on the wall. So, you can see how the charging system is operating without walking outside to visit the controller.

 

[Draddog2169]

I like the idea of a tracer In both regards. I understand what you are saying. You are teaching me a lot about solar. My cabin is 90 feet from my batteries and SunGold unit. I would love to monitor it from the cabin.
Can we move to the solar array. I have 4 panels at this time. I do not have a combiner, but feel that maybe I should have one. When I move the array and add 2 more panels I am thinking I should definitely purchase a combiner. Am I correct on stating this.

 

[MichaelK]

I like the idea of a tracer In both regards. I understand what you are saying. You are teaching me a lot about solar. My cabin is 90 feet from my batteries and SunGold unit. I would love to monitor it from the cabin.
Can we move to the solar array. I have 4 panels at this time. I do not have a combiner, but feel that maybe I should have one. When I move the array and add 2 more panels I am thinking I should definitely purchase a combiner. Am I correct on stating this.

What are the specifications on your exact panels? Do they have a Vmp of 18-20V? What I am mostly doing is wiring four 30V residential panels in series for my arrays, with a Vmp of 120VDC. Here is a pic below of one of my 4-panel arrays. If your panels indeed have a Vmp of ~20V, then you could put all six into a single series string, if using the 6420 controller. But, we really need the exact specs to make a decision.

According to code, a combiner is only required with more than two series strings, but incorporating a combiner adds flexibility besides just safety. When troubleshooting problems, I can simply flip a breaker, and determine how much power one individual string is producing. Midnight Solar makes 3, 6, and 12 bay combiners. You simply pop in the correct amperage breaker for your system, and then each string can be flipped of at the touch of a finger.

 

[DaddyBUDsDoorags]

No, you cannot parallel 12 volt and 24 volt batteries.

I know that...2in series=24
2 strings of 24v in parallel.
I wasn't clear...but it's totally possible since the manual covers this configuration.