pile of parts

[bcroe]

A good 15 amp MPPT controller will cost $200.

True, but these prices have seemed too steep to me for a while. The common switcher box used in PCs handles
120-240 input ranges and delivers regulate outputs in that power range, on sale at $20. The unisolated MPPT
does less (no AC-DC section); the MPPT function change is negligible cost. Not saying they should be that cheap
with lower market volume, but the gap should be smaller. Bruce Roe

[Sunking]

my biggest load is my compressor, 20 (startup amps)

20 amps at what voltage? 20 amp does not mean anything.

20 amps @ 1.2 volts is 22 watts a high powered LED flashlight
20 amps @ 12 volts is 240 watts, a RV TV and Stereo
20 amps @ 120 volts is 2400 watts, a dryer
20 amps @ 240 volts is 4800 watts, a dryer plus hot water heater.
20 amps at 2400 volts is 480,000 watts a factory or a Walmart
20 amps on a utility 1,000,000 volt line supplies a small city of 20,000 homes on the same size wire of all above

20 amps does not mean squat.

[TheGuyFromNJ]

20 amps at what voltage? 20 amp does not mean anything.

20 amps @ 1.2 volts is 22 watts a high powered LED flashlight
20 amps @ 12 volts is 240 watts, a RV TV and Stereo
20 amps @ 120 volts is 2400 watts, a dryer
20 amps @ 240 volts is 4800 watts, a dryer plus hot water heater.
20 amps at 2400 volts is 480,000 watts a factory or a Walmart
20 amps on a utility 1,000,000 volt line supplies a small city of 20,000 homes on the same size wire of all above

20 amps does not mean squat.

I'm sorry I wasnt clear, my air compressor is 120v 20amp to start.

[Sunking]

I'm sorry I wasnt clear, my air compressor is 120v 20amp to start.

OK that is easy to do and not near as expensive as you might think. Ready to listen to a conservative with real solutions?

• Wire the 2 panels in series.
• Buy a Morningstar SunSaver 15 amp MPPT Controler ($200)
• Buy a pair Trojan T-105's golf cart batteries and wire them in series. They are 6 volt golf cart batteries and can supply your gizmo for 4 hours standing on their head, under water, and holding their breath. About $300 for the pair. You can nail them with 200 amps easily for startup. Golf carts can pull up to 600 amps for a moment at start up, and supply 50 amps for 4 hours if needed. 1 hour a day easily blindfolded with their hands tied behind their back with a 1/2 a brain.

Does that make you

[karrak]

Maybe I'm thinking too big....

my biggest load is my compressor, 20 (startup amps)for maybe 20-30 minutes a week, my 6 ac lights are 192w total 8-10 hours/week, there is a time when both are used at the same time.
Maybe I don't need such a big system. How much battery do I need to start a 20a compressor?

I apologize in advance if it seems like I am trying to beat a dead horse.

Is your current setup capable of starting your compressor and running your other equipment at the same time?

There are several things to consider when looking at your power/energy requirements.

The first is the maximum amount of instantaneous power that your system needs to provide. In your case it is 192W +20x120 = ~2.6kW. This is the maximum amount of surge power that your inverter and battery must be able to supply.

The second is your average power usage. Once the compressor has started, its running current might reduce to 4A so the amount of power that you need on a continuous basis is 192W +4x120 = ~0.7kW. Your compressor is not on all the time but you are using other power tools so lets say your average power usage is ~1kW.

If these figures are correct I would think your current inverter and battery (if it is in a workable condition) would easily run your loads.

The next thing to consider is how much energy you have to have stored in your battery to supply the power you need for the time you need. Let us say you work in your shed for four hours. The total amount of energy you need would be 1.0kW x 4 which equals 4kWh. We have to subtract the power losses in the inverter and battery so would end up with your consumption being somewhere around 5kWh.The amount of energy stored in your battery is the battery capacity in Ah x battery voltage so in your case 9x114x12 =~12.3kWh.

The next thing is the amount of power from the solar panels needed to recharge the battery. You currently have two 100W panels. Each hour in ideal sunshine conditions your panels will provide 0.2kWh of energy to recharge your battery.In reality and due to losses this is more likely to be around 0.15kWh. To recharge the 5kWh you have used would take at least 33 hours of sunshine.

So you are correct in thinking that you need to increase the number of solar panels. If you add the five 220W panels to your system you recharge time reduces to around 5 hours of sunshine.

As you only use the system on a part time basis it is possible that your battery is still in reasonable condition. You will have to run some discharge tests to see if this is the case.

If you add the panels and solar controller or two I would think your current setup assuming the battery is OK will continue to work for you. If you want to increase your power consumption looking at converting to 24 volts or even 48 volts would be a good idea.

Simon

Off grid 24V system, 6x190W Solar Panels, 32x90ah Winston LiFeYPO4 batteries installed April 2013
BMS - Homemade Battery logger
Latronics 4kW Inverter, homemade MPPT controller

[TheGuyFromNJ]

Yes my current setup runs my garage, but the charge time is the problem.

So if I wanted to invest no more money. ..

what If a guy (not unlike me) paralleled four of these 200 W panels to my crappy 30 amp CC and reduced the batteries down to 4 or 6 at 12v 116ah each in parallel?

I know at some point the reduction in batteries reduces the amount of amps available for the inverter to feed the compressor on start up, (in-rush), also at some point the amount of batteries exceeds the CC ability to recharge, is there a happy medium? I just don't know how that is calculated.

btw, the inverter is a pure sine 1800w, 3960w peak with inrush delay.

[Sunking]

I know at some point the reduction in batteries reduces the amount of amps available for the inverter to feed the compressor on start up, (in-rush), also at some point the amount of batteries exceeds the CC ability to recharge, is there a happy medium? I just don't know how that is calculated..

Super easy 5th grade math even Karrak can figure out with some help with a teacher and calculator in hand. Rest of us can do it in our heads.

It is called C-Rates where C is the battery AH Capacity. Flooded Lead Acid Batteries need at least a C/12 minimum Charge rate, Maximum charge rate and discharge rate is typically C/8. Some can go higher up to C/6, and some AGM's can do 1C. The numbers 8 and 12 are hours.

So here is how the math works.

AH = Amps x Hours.See told you that was easy.

from that we can also rearrange the formula to:

Amps = Amp Hours / Hours

and

Hours = Amp Hours / Amps.

Again just simple 5th grade algebra. Think of Amp as dollars, and hours as hours. How many hours do you have to work to make $100 if you make $10 per hour.

So let's say you have a 80 AH battery. What is the maximum current you can discharge/charge at? Well we know that is C/8. So 80 AH / 8 Hours = 10 amps. What is the minimum charge rate.

So what is the minimum charge rate. Again we know C/12, so 80 AH / 12 hours = 6.67 amps.

OK when you see a specified battery capacity most use what is called the 20 Hour rate or C/20. So a 80 AH battery is telling you you can discharge that battery at 4 amps for 20 hours, or 80 AH / 20 H = 4 A. This is kind of important with respect to Peukerk Law that says the faster you discharge a battery, the less capacity it has. Going back to the 80 AH battery if you discharge at 8 amps or the 10 hour rate is faster than 20 hours. The capacity is reduced to around 60 AH. Discharge at say 2 hours and you are down to 25 AH. So the faster you discharge, the less capacity you actually have. Commercial and Industrial batteries specify at 4, 6 and 8 hours. So if that 80 AH consumer battery were a commercial battery rated at 8 hours would be specified as 55 AH rather than 80 AH. They spin the numbers. Consumer batteries ar exaggerated.

Easy peasy.

[karrak]

what If a guy (not unlike me) paralleled four of these 200 W panels to my crappy 30 amp CC and reduced the batteries down to 4 or 6 at 12v 116ah each in parallel?

We need to know what voltage the 220W panels are. If they are 24 Volt panels (Vmp around 35 volts) putting them on a 12 volt PWM controller will reduce the power available from each panel to around 120W.

Your current 100W panels if they are 12V panels (Vmp around 18 volts) will charge your battery at around 10-12A in full sunshine.

Replacing the 100W panels with three 220W panels would increase this to around 27A if they are 24 volt panels. Make sure that your controller will work with 24V panels otherwise it might go up in smoke.

As you are using the battery on an irregular basis with gaps between use I don't think that maintaining a minimum charge rate of C/12 (in your case 87A) is so important.

I know at some point the reduction in batteries reduces the amount of amps available for the inverter to feed the compressor on start up, (in-rush), also at some point the amount of batteries exceeds the CC ability to recharge, is there a happy medium? I just don't know how that is calculated.

The larger the battery, the less stress you put on it with startup loads and the less charge as a percentage you take from the battery when you use it. Both these things will increase the longevity of your battery. As you already have your 9 batteries in parallel set up I would leave the arrangement as it is. Have you had a look at the article on how to wire batteries in parallel I linked to earlier?

Simon

Off grid 24V system, 6x190W Solar Panels, 32x90ah Winston LiFeYPO4 batteries installed April 2013
BMS - Homemade Battery logger
Latronics 4kW Inverter, homemade MPPT controller

[Sunking]

what If a guy (not unlike me) paralleled four of these 200 W panels to my crappy 30 amp CC and reduced the batteries down to 4 or 6 at 12v 116ah each in parallel?

You cannot use the 200 watt panels on a 12 volt battery with a PWM controller. I do not need to see the specs because there is no such thing as a 200 watt 12 volt battery panel.If you did two things happen and neither is good.

1. Very dangerous asking for trouble. That should be a good enough reason.

2. Incompatible with a PWM controller. 200 watt panels have a Vmp = 36 to 37 volts and Imp of 5.5 amps. Connect them in parallel gives you 36.5 volts @ 16.7 amps. On the output gives you 12 volts @ 16.67 amps of just 200 watts from 600 watt input. Exact same power you would get from 3 x 100 watt panels. Have any problem with that?

Ignore Karrak, he is a fraud and dangerous. 27 amps my arse Karrak.

[Sunking]

Replacing the 100W panels with three 220W panels would increase this to around 27A if they are 24 volt panels. Make sure that your controller will work with 24V panels otherwise it might go up in smoke.

You really do not now WTF you are talking about and very dangerous. For Pete Sake you are suggesting someone intentionally use a 60 to 72 cell panel into a PWM controller to charge a 12 volt battery. Do you not understand how stupid dangerous you are pretending to be an expert? Obviously not.

Let's see it that gets you a vacation. You just hung yourself again.

[Mike90250]

We need to know what voltage the 220W panels are. If they are 24 Volt panels (Vmp around 35 volts) putting them on a 12 volt PWM controller will reduce the power available from each panel to around 120W.

Your current 100W panels if they are 12V panels (Vmp around 18 volts) will charge your battery at around 10-12A in full sunshine.

Replacing the 100W panels with three 220W panels would increase this to around 27A if they are 24 volt panels. Make sure that your controller will work with 24V panels otherwise it might go up in smoke........

I have highlighted the important part of Simon Karrak post.

It is very important that you realize the quality of information that you get for free over the internet, It's worth at least as much as you paid for it,
In this case, it's going to cost you $$ if you implement this idea. I honestly don't know what Karraks purpose is, because he is now on a vacation from this forum,
and it does not matter a bit to me, because it's bad information . Correction, it's dangerous information, connecting parts to parts and then stating "but it might just go up in smoke"

Moderator

[TheGuyFromNJ]

Ok thanks for all the info. I'll have to rethink my whole plan.

Btw, these are
pmax 220w
vmp 29.2v
lmp 7.53
voc 36.6

[Sunking]

Ok thanks for all the info. I'll have to rethink my whole plan.

Btw, these are
pmax 220w
vmp 29.2v
lmp 7.53
voc 36.6

OK if you parallel the three panels, the input current into the PWM controller is 3 x 7.53 amps = 22.59 amps. That means the output current is 22.59 amps into a 12 volt battery = 271 watts from 660 watts of panel power. The issue is the PWM controller. Now if that were 24 volt batteries everything is fine and dandy. Still the same 22.6 amps but at 24 volts is 540 watts from 660 watts of panels.

Now with that said, you can use those 220 watt panels with a 12 volt battery. To do that requires using at least a 55 amp MPPT Controller. If you do that then Output Current = Panel Wattage / Battery Voltage, or 660 watts / 12 volts = 55 amps. Guess what? 12 volts x 55 amps = 600 watts. With the right MPPT controller you can wire the panels in series so you go in with 87.6 volts @ 7.53 amps, and out at 12 volts @ 55 amps.

[Sunking]

I honestly don't know what Karraks purpose is, because he is now on a vacation from this forum,

Second time, maybe he will take the hint and not come back.By his own admission only came here to harrass me.

[karrak]

I have highlighted the important part of Simon Karrak post.

It is very important that you realize the quality of information that you get for free over the internet, It's worth at least as much as you paid for it,
In this case, it's going to cost you $$ if you implement this idea. I honestly don't know what Karraks purpose is, because he is now on a vacation from this forum,
and it does not matter a bit to me, because it's bad information . Correction, it's dangerous information, connecting parts to parts and then stating "but it might just go up in smoke"

Moderator

I am sorry Mike but you are wrong. Most of the cheap PWM controllers sold at the moment are dual 12/24V. A dual 12/24V controller is safe to use with a 24V panel and a 12 volt battery and so is a 12V only controller that can safely handle the V_OC of a 24V panel. I was issuing a warning to the OP to check that his PWM will work with 24 volt panels before going ahead.

It is not very efficient to use a 24V panel with a 12V battery as it cuts the power supplied by the panel by a little less than 50% compared to using a 24V battery. In this situation it might make sense because the OP had previously stated that he already has 5 220W panels with a Vmp of 29.2V and didn't want to spend any more money.

I don't need to be lectured about safety. My last paying design project was to design a piece of equipment for commercial use that connects to the PSTN (telephone network) from the ground up. Hundreds of the instruments I designed and manufactured are still in use today. Do you have any idea how many safety requirements you have to design into equipment that is connected to the PSTN and how much testing the equipment has to undergo before it can be legally connected?

Simon

Off grid 24V system, 6x190W Solar Panels, 32x90ah Winston LiFeYPO4 batteries installed April 2013
BMS - Homemade Battery logger github.com/simat/BatteryMonitor
Latronics 4kW Inverter, homemade MPPT controller