Power requirements dc solar system/Connect 12 v pannels and charge controller to 24v

[jacob84401]

I need to run a 1.5 hp motor (1.5 hp X 746 watt/hp=1120 watt) using 12 v batteries and a solar pannel. I will write out my math so you can check if my logic is sound. I need to run this motor for 5 minutes every 12 hours. (8 am and 8 pm) I will keep to this schedule for 6 days and then I will have a break for 2 weeks. It is very important that the motor be able to run so even if it is over cast for a couple days straight.

The problem I am having is that I am not sure what size panel I need. I think I can calculate it but there are some variables that I am not sure of.

1. how many hours of max power output can I expect from the solar panel each day?
2. Assuming I use 12 volt deep cycle batteries (how many will I need?) simple rv batteries
3. I can run my system off of 12 v or 24 v. Is there a way to use a 12 v panel and a 12 volt charge controller to charge a 24 volt system?
4. I can't decide to go with a 12 or 24 volt system. I am not sure if why one would be better than the other. I hear rumors that higher voltage means higher rpm where higher amps (connecting 2 12 v batteries in parallel) means more torque. Is that true? Or does rpms only depend on the motors manufacturing? IS there any advantages to using a 24 volt system?
5. What size panel will I need?

Also there will be some remote control equipment that will need to run on standby all the time it shouldn't draw more than 40mA @ 12 v (v*I=0.48 W)

I am completely new to this and will probably need a lot of help so have patience.

In case anyone was wondering it will be used to replace a gas motor for a Wheel Line mover (part of an irrigation system).

[inetdog]

I need to run a 1.5 hp motor (1.5 hp X 746 watt/hp=1120 watt) using 12 v batteries and a solar pannel. I will write out my math so you can check if my logic is sound. I need to run this motor for 5 minutes every 12 hours. (8 am and 8 pm) I will keep to this schedule for 6 days and then I will have a break for 2 weeks. It is very important that the motor be able to run so even if it is over cast for a couple days straight.

The problem I am having is that I am not sure what size panel I need. I think I can calculate it but there are some variables that I am not sure of.

1. how many hours of max power output can I expect from the solar panel each day?
2. Assuming I use 12 volt deep cycle batteries (how many will I need?) simple rv batteries
3. I can run my system off of 12 v or 24 v. Is there a way to use a 12 v panel and a 12 volt charge controller to charge a 24 volt system?
4. I can't decide to go with a 12 or 24 volt system. I am not sure if why one would be better than the other. I hear rumors that higher voltage means higher rpm where higher amps (connecting 2 12 v batteries in parallel) means more torque. Is that true? Or does rpms only depend on the motors manufacturing? IS there any advantages to using a 24 volt system?
5. What size panel will I need?

Also there will be some remote control equipment that will need to run on standby all the time it shouldn't draw more than 40mA @ 12 v (v*I=0.48 W)

I am completely new to this and will probably need a lot of help so have patience.

In case anyone was wondering it will be used to replace a gas motor for a Wheel Line mover (part of an irrigation system).

A. Thank you for listing both the motor rating and the time schedule. You would be surprised (maybe) how many people leave that out. But there are lots of different kinds of ways of getting 1.5 HP, using different types of motors and AC or DC. You really need to figure out what kind of a motor you can use, since you are replacing a gas engine rather than supplying power to an existing motor.
B. The 12 versus 24 volt question is only on the DC side of an inverter, if used, and will have no relation to the speed or torque of an AC motor. It will affect a DC motor, but the motor itself will be designed for a particular voltage. 24 is better for high power since you can use smaller wiring (higher voltage means lower current for the same power.) I doubt that you will find a 1.5HP motor that runs on 12 volt. That would be pulling more than 100 Amps when starting. You might actually end up with a 48 volt DC motor.
C. The batteries are going to have to be carried along, so the weight may end up being a problem.
D. For intermittent high power use and for lowest weight, you may have to use AGM batteries. More on that in a later post.
E. You cannot use a 12 volt panel and charger for a 24 volt system. It would require going out to rewire the charger a couple of times per day, which I suspect you would like to avoid, and it would not do a good job anyway.

[Sunking]

You are going to run into a huge problem with the battery. Depending on the efficiency of that motor it will draw some 1200 to 1500 watts from the battery. At 12 volts you are talking 100 to 125 amps.

Here is the problem batteries have internal resistance, and when you draw current through a battery with resistance the voltage drops called IR losses. Voltage = Current x Resistance = IR. If that voltage drop is significant more than .5 volt or more, your inverter will trip off line from under voltage. So doing a little math at 100 amps with .5 volts means a resistance of more than .005 Ohms will be a problem. YOu wil be lucky to even keep the wiring and connector resistance lower than .005 Ohms, and that is not including the battery internal resistance yet that has to be added on.

OK here is the Meat On The Bone. For Flooded Lead batteries they can deliver roughly C/8 current before Voltage drop gets to be a problem. C = the battery AH capacity at the 20 hour discharge rate. That means if you need 100 amps, you need a 800 AH battery. You are talking about a 600 pound battery at 12 volts that will cost you some $1500 to $2000.

For a AGM battery general rule is no more than C/4 discharge. So for a AGM you would need around a 400 AH battery. It ways about 1/3 the weight of a 800 AH FLA but there is a catch. A 400 AH AGM battery cost as much as a 800 AH FLA.

If you insist on 12 volts the only 12 volt battery I know of that can work is an Optima Yellow Top D34 with a internal resistance of .0028 Ohms.

[jacob84401]

A. Thank you for listing both the motor rating and the time schedule. You would be surprised (maybe) how many people leave that out. But there are lots of different kinds of ways of getting 1.5 HP, using different types of motors and AC or DC. You really need to figure out what kind of a motor you can use, since you are replacing a gas engine rather than supplying power to an existing motor.
B. The 12 versus 24 volt question is only on the DC side of an inverter, if used, and will have no relation to the speed or torque of an AC motor. It will affect a DC motor, but the motor itself will be designed for a particular voltage. 24 is better for high power since you can use smaller wiring (lower voltage means lower current for the same power.) I doubt that you will find a 1.5HP motor that runs on 12 volt. That would be pulling more than 100 Amps when starting. You might actually end up with a 48 volt DC motor.
C. The batteries are going to have to be carried along, so the weight may end up being a problem.
D. For intermittent high power use and for lowest weight, you may have to use AGM batteries. More on that in a later post.
E. You cannot use a 12 volt panel and charger for a 24 volt system. It would require going out to rewire the charger a couple of times per day, which I suspect you would like to avoid, and it would not do a good job anyway.

B- Thanks for your response you've provided me with a lot of good information. When you said "(lower voltage means lower current for the same power.)" did you mean lower voltage means higher current? I thought I understood this concept but I want to make sure. I would like to use DC over AC just because I think it might be cheaper if I don't have to get an inverter. (I could be wrong on this. If it were cheaper to get an inverter and use ac I am all for that. If I am not mistaken it would be cheaper and easier to find a 1.5 hp motor that uses AC power.) I am not too sure if I care about the size of the wiring just because I may only need 3' of wire to go between the batteries to the motor. (the solenoid I use might not like 100+ amps going through it though) I don't have anything against using a 48 volt dc motor but if I have to connect 4 car batteries together it will be heavy and expensive. (I would be open to other battery options as long as they were cheap.) One of the reasons I am partial to 12 volt is because my remote control receiver runs off of 11 to 14 volts.

E- That is very good to know about the charge controller. I assume that means I can't get a cheap harbor freight 12 volt solar panel and expect to run a 24 v system. (Well if I get 2 panels and wire them in series? who knows?) There's probably a better place to by panels but that will come later.

As for the motor I am not even sure what RPM's will be needed. I am trying to figure that out. All I know is that some other company makes a similar conversion kit and they use a 1.5 hp motor.

[inetdog]

B- Thanks for your response you've provided me with a lot of good information. When you said "(lower voltage means lower current for the same power.)" did you mean lower voltage means higher current?

Thanks for calling my attention to the mindo. (variation on typo). I have fixed it.

[jacob84401]

You are going to run into a huge problem with the battery. Depending on the efficiency of that motor it will draw some 1200 to 1500 watts from the battery. At 12 volts you are talking 100 to 125 amps.

Here is the problem batteries have internal resistance, and when you draw current through a battery with resistance the voltage drops called IR losses. Voltage = Current x Resistance = IR. If that voltage drop is significant more than .5 volt or more, your inverter will trip off line from under voltage. So doing a little math at 100 amps with .5 volts means a resistance of more than .005 Ohms will be a problem. YOu wil be lucky to even keep the wiring and connector resistance lower than .005 Ohms, and that is not including the battery internal resistance yet that has to be added on.

OK here is the Meat On The Bone. For Flooded Lead batteries they can deliver roughly C/8 current before Voltage drop gets to be a problem. C = the battery AH capacity at the 20 hour discharge rate. That means if you need 100 amps, you need a 800 AH battery. You are talking about a 600 pound battery at 12 volts that will cost you some $1500 to $2000.

For a AGM battery general rule is no more than C/4 discharge. So for a AGM you would need around a 400 AH battery. It ways about 1/3 the weight of a 800 AH FLA but there is a catch. A 400 AH AGM battery cost as much as a 800 AH FLA.

If you insist on 12 volts the only 12 volt battery I know of that can work is an Optima Yellow Top D34 with a internal resistance of .0028 Ohms.

Your right I am expect to draw at least 1200 watts. I do only plan on running the motor for 5 min (0.083 hr) every 12 hours. I figure that puts it at .0096 kwh (1.2*.083). Is it unreasonable to figure that 2 car batteries can provide that. life=ah rating/amps drawn If I use a 12 volt battery P=VI (I=1200/12=100 amps if I use 24 volt -> 50 amps) life(hr)=60 AH/100=.6hr and that is with a low rated battery and only one battery .6hr>.083hr. If I were to use 2 batteries with a 100 amphr rating and hooked them in series (life=200amp hr/50amp=4hr) From my very limited knowledge (I am studying to be a mechanical Engineer) on electricity it looks like I could run the motor for 4 hrs before the battery goes dead. Now like I said I have very little knowledge on this subject but I would like to understand where the above calculations go wrong. Please explain to me why this doesn't work.

I do know that here is someone who builds these kits to convert wheel line movers to solar power and he uses 2 12v deep cycle rv batteries to run a 1.5 hp motor.

[Sunking]

Your right I am expect to draw at least 1200 watts. I do only plan on running the motor for 5 min (0.083 hr) every 12 hours. I figure that puts it at .0096 kwh (1.2*.083). Is it unreasonable to figure that 2 car batteries can provide that. life=ah rating/amps drawn

It is not the watt hours that is the problem here, it is the high demand of 1200 watts on a 12 volt battery, and the internal resistance of said battery, plus needing to oversize the panel wattage to keep up such a large capacity battery. With me so far?

In th eLead Acid battery family there are 3 major groups or classes of batteries being SLI (starting, lighting, and ignition aka Cranking and Starting you use in a vehicle), Hybrid (RV, Marine, and Golf Cart), and Deep Cycle. They are designed and built to do specific task.

SLI batteries are designed with multiple thin spongy textures plates to increase plate surface area. This provides for very low internal resistance so they can deliver very high amounts of short burst of current used to crank and engine, then be very quickly recharged by the vehicle alternator. They make for very poor cycle use, and if pressed into cycle service only have very few cycles in them an dwill not last. The plates will just corrode and sulfate then fall into the bottom of the jar.

Deep Cycle batteries are designed with fewer plates than SLI but very heavy thick plates which is perfect for deep cycling. If depth of discharge (DOD) is limited to 20% or less can have a cycle life up to 4000 cycles. The trade off with thick heavy plates is higher internal resistance, thus subject to limited charge and discharge rates. Fo rFLA C/8 is as high as you want to go, and for AGM C/4 is abou tas hard as you want to push those.

Hybrid Batteries, pay attention here because this is where you want to go. Are designed with fewer plates than SLI, but are heavier than SLI. The Hybrid has more plates than Deep Cycle but thinner. So what is obvious is the hybrid is in between SLI and Deep Cycle. It is an attempt to have th ebest of both, but falls short of the extremes. They cannot provide the extremely high currents of SLI, nor do they have the cycle life of Deep Cycle. Unfortunately you cannot have it both ways. The stupid Law of Physics get in the way. What you do get is a decent trade-off. Now for the Hybrids is where you want to look, specifically at the AGM flavor used in UPS systems and to a lessor extent the RV-Marine- Golf Cart varieties.

So with a 1200 watt load at 12 volts is 100 amps = 1200 watts / 12 volts anyway you spin the numbers. Inverters are picky little SOB's and have undervoltage Shut-Offs typically set at 11 volts. Catch here is motors are constant power users. A 1200 watt, 12 volt motor draws 85 amps at 14 volts, and 120 amps at 10 volts. So at the minimum input to the inverter the magic number to never go below is 11 volt Under-voltage Trip point. So the current at 11 volts with a 1200 watt load is 1200 watts / 11 volts = 109, so let's just say 110 amps.

So here is the challenge. A fully charged up 12 volt battery at rest is 12.6 volts. That only gives you 1.6 volts of wiggle room before the whole thing shuts down. Total resistance of the wiring, connections, and battery has to be less than 1.6 volts / 110 amps = .0145 Ohm.s You are going to have a expensive time just keeping the wiring and connection resistance under .0145 Ohm's, but you have the battery to worry about too as it is part of the total circuit resistance. Understand now?

For example the smallest copper guage wire in free air you can use safely at 110 amps is 4 AWG RHW. 4 AWG copper has a resistance of .31 Ohm/Kft. That means anything over 5-feet 1-way is over your .0145 limit. Only way to overcome that is to use much larger wire.

So this takes us back to the battery. The best fit for your application is the Optima Battery I linked too earlier. It is only a 55 AH battery, but has a internal resistance of .0028 Ohm's. It will only require you to use a 50 to 100 watt solar panel with a 10 amp charge controller. That is the cheapest and lightest route you can get.

[Naptown]

Just curious what is the purpose for this. Sounds like a garage door opener

[inetdog]

Just curious what is the purpose for this. Sounds like a garage door opener

OP:
...Wheel Line mover (part of an irrigation system)

When you have an irrigation system that has a long run of pipe mounted on large narrow wheels, you deliver water to a rectangular area with the pipe stationary and then have to move the line of pipe on to the next position.

I believe that center pivot irrigation, on the other hand, uses water power to move the pivoted pipe continuously whenever the water is turned on.

[jacob84401]

When you have an irrigation system that has a long run of pipe mounted on large narrow wheels, you deliver water to a rectangular area with the pipe stationary and then have to move the line of pipe on to the next position.

I believe that center pivot irrigation, on the other hand, uses water power to move the pivoted pipe continuously whenever the water is turned on.

Good explanation. The center pivot actually uses electricity to move. Water is not that reliable. It makes it really hard because each of the wheels on a pivot have to turn at a different speed.

As for the wheel line the gas motors just are not that reliable and also in order to move the line you have to walk into the middle of your field to the mover and then move it. This takes time (the lines are generally a 1/4 mile long) and you tramp a path through your crop every time you go out and back.

[jacob84401]

Okay so it sound like I will need to use a marine type battery. I actually did some more research and it turn out that I was wrong when I said that they were using deep cycle type batteries. I are actually using a marine battery. I might be crazy but I heard something about a group 27 type battery. I'll look more into that.

Now I am starting to wonder about sizing of the solar panel and charge controller. During an average day how many hours can I expect to get max output of my solar panel? Or with that what can I expect for partial lighting. And what factor of safety (maybe compensation is a better word).

[inetdog]

I might be crazy but I heard something about a group 27 type battery. I'll look more into that.

The Group number for a battery just standardizes its outside dimensions and terminal location. It says nothing about capacity or performance.