So, I’m thinking of setting up a system to supply power to a window A/C Unit (500-700 watts) from 3-8pm during the summer months here in Phoenix. Since most of that time there will be sunlight and solar panels are cheaper than batteries, I’m thinking of getting enough solar panels so I can run the AC just on them (even when it’s cloudy), except for maybe the last couple of hours. I plan to have a battery where 1200-2400 watts hrs. will be available to use. The question I have, is that on a bright day, and the A/C not running, the panels could be producing 1800+ watts of power which presumably the solar controller will direct that to the discharged battery. I don’t want that much power going into my empty battery as it would be excessive and either reduce it’s life and/or trip the BMS (if it’s a lithium 12v 100ah battery). I believe, in general, lead acid batteries maximum C rate is even lower then lithium and is .3 (AGM) or less. So, can I regulate the controller so it will provide enough power to run/not run the A/C Unit and charge the battery at a safe C rate. Or am I making something out of nothing. Hope this make sense.
Preventing a Battery of getting a charge rate (C) from a solar controller greater then what the battery is rated for.
- Thread starter DASH
- Start date
Thanks Kernel
If your charge controller is rated for the maxC of the battery, the solar should just go to waste when not demanded.
The panels supply only what the mppt charge controller "calls" for, so to speak. It will never overcharge your battery. Also, it will never deliver more amps than it is rated for. (These points assume that the controller is set up correctly for your battery type).
You also brought up a good point to consider: If you want to operate a steady-state load of 700w, you will need at least 60a or so, at 12v, just to keep up. You probably will want to have a 24v battery setup (30a from the controller to the battery) or 48v (15a). And you will need some additional amps from the controller to charge the battery simultaneously.
The forum has a great energy audit/system sizing sheet here:
diysolarforum.com
You also brought up a good point to consider: If you want to operate a steady-state load of 700w, you will need at least 60a or so, at 12v, just to keep up. You probably will want to have a 24v battery setup (30a from the controller to the battery) or 48v (15a). And you will need some additional amps from the controller to charge the battery simultaneously.
The forum has a great energy audit/system sizing sheet here:
System Energy Audit and Sizing Spread Sheet
To get the spreadsheet, click on the orange button at the top of this page. This sheet is intended to help you plan your system. Fill it out down to the last decimal place, look at the results..... and then make your best guess;) Notes...
diysolarforum.com
ghostwriter66
"Here - Hold my Beer"
SCC senses what your battery needs and then draws that from the panels ... your not going to overcharge unless you set the voltage toooo high on the SCC
Hi Ghostwriter. I'm not concerned about overcharging, I'm concerned about charging batteries at a high amperage. For Example (This is an extreme situation) . I have Solar Panels and a Controller that is capable to charge a 12 volt battery at 120 amps. I have a 12 volt 100 amp hr AGM battery that has a maximum charge rate of .3C, and is at 50% capacity. Will the battery initially receive 120 charging amps, from the controller (as it's capable to deliver that) or will the controller regulate the amperage to a maximum .3C rate (maximum charge rate for the battery) which in this case would be about 33 amps. Thanks.
Do you have a specific SCC that you are asking about?
Look at the SCC manual.
You choose the battery type profile in the SCCs programing for AGM. Sealed. Flooded or User etc so the SCC will only output what an AGM battery can handle.
If you had the profile on the wrong battery type or inputted too high or low of setting in the User profile then you could damage the battery.
Look at the SCC manual.
You choose the battery type profile in the SCCs programing for AGM. Sealed. Flooded or User etc so the SCC will only output what an AGM battery can handle.
If you had the profile on the wrong battery type or inputted too high or low of setting in the User profile then you could damage the battery.
I have a EPEVER 40AMP Controller. Yes, it does have settings (Sealed, GEL, Flooded, or User), but I don't see how or where the Controller limits the amperage according to the battery (perhaps it's automatic? ) I know that some lithium batteries can have different recommended C rates, and I don't see a setting for that including the User settings. (Maybe someone knows where it is). I'm figuring, maybe the way to control the C rate is getting the right mixture of solar panels and batteries.
Bill Taylor
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Hey DASH. I will just jump in here and give my opinion. I'm pretty good at that ?.
If you're planning to run loads other than the air conditioner, you might want to go for option one. But if it's just for the air conditioner and nothing else, option two is probably a lot better idea.
#1 - If you are going with solar modules, batteries, and inverter scenario. You will need a large enough battery bank to accept the power those panels can put out. I don't recall seeing a charge controller with a current limiting function. It doesn't matter where you set the voltage, or what charge profile the controller is set on. If you have 100 amps available, and your battery is low, the charge controller will try to charge at 100 amps. That will result in the voltage rapidly rising, but it can also damage the battery. You mentioned 1800 watts. That could be as much as 150 amps at 12-volts, 75 amps at 24 volts, etc. If you go that high with your solar, I would be looking at a minimum of six golf cart batteries. (Assuming a 12v system) I know that's probably more than you were expecting, but that will also allow you to run the air conditioner into the evening after the sun's gone down.
#2 - It's not really a secret, but it seems there are not too many people that know about this. APS allows its customers to install grid-tie systems of 1000 Watts or less without any contract, special disconnects, or even a site visit from them. They don't even require notification. That will easily give you 5 or 6 KW each day. Which would go a long way toward covering the usage from your air conditioner. No battery, no inverter, no hassle, cheap simple and easy. If you shop around, you should be able to pick up everything you need (used) for around $500. Of course, you may be required to get a building permit, that would be up to you. All you need to do is run a few wires into a breaker in the bottom of your load center. Pretty straightforward stuff. I don't know about SRP or other utilities. But I know at least half a dozen people on APS who has been running unpermitted 1kw grid-tie systems for over a year. No problems at all. Works like a champ!
Good luck.
If you're planning to run loads other than the air conditioner, you might want to go for option one. But if it's just for the air conditioner and nothing else, option two is probably a lot better idea.
#1 - If you are going with solar modules, batteries, and inverter scenario. You will need a large enough battery bank to accept the power those panels can put out. I don't recall seeing a charge controller with a current limiting function. It doesn't matter where you set the voltage, or what charge profile the controller is set on. If you have 100 amps available, and your battery is low, the charge controller will try to charge at 100 amps. That will result in the voltage rapidly rising, but it can also damage the battery. You mentioned 1800 watts. That could be as much as 150 amps at 12-volts, 75 amps at 24 volts, etc. If you go that high with your solar, I would be looking at a minimum of six golf cart batteries. (Assuming a 12v system) I know that's probably more than you were expecting, but that will also allow you to run the air conditioner into the evening after the sun's gone down.
#2 - It's not really a secret, but it seems there are not too many people that know about this. APS allows its customers to install grid-tie systems of 1000 Watts or less without any contract, special disconnects, or even a site visit from them. They don't even require notification. That will easily give you 5 or 6 KW each day. Which would go a long way toward covering the usage from your air conditioner. No battery, no inverter, no hassle, cheap simple and easy. If you shop around, you should be able to pick up everything you need (used) for around $500. Of course, you may be required to get a building permit, that would be up to you. All you need to do is run a few wires into a breaker in the bottom of your load center. Pretty straightforward stuff. I don't know about SRP or other utilities. But I know at least half a dozen people on APS who has been running unpermitted 1kw grid-tie systems for over a year. No problems at all. Works like a champ!
Good luck.
Ok... look.
A charge controller with 120A capability will charge the battery with a maximum VOLTAGE set by the type setting. The battery will not draw more amps than it’s internal resistance will allow... the only way to damage the battery is if the VOLTAGE goes too high, and the charge controller will not exceed the type settings... it doesn’t matter if the controller is capable of 120A... a voltage limit for bulk or float rate is built into the controller settings.
A charge controller with 120A capability will charge the battery with a maximum VOLTAGE set by the type setting. The battery will not draw more amps than it’s internal resistance will allow... the only way to damage the battery is if the VOLTAGE goes too high, and the charge controller will not exceed the type settings... it doesn’t matter if the controller is capable of 120A... a voltage limit for bulk or float rate is built into the controller settings.
When you "run AC off solar" youre running AC off a battery first and foremost. Youre always charging with 1800w whether the AC is running or not. Discharge and charge rates are the same so you need an appropriate size battery either way you slice it.
Outback and midnight solar current limit, fyi.
Outback and midnight solar current limit, fyi.
My system as any other i have pushed buttons on will jam whatever the current setting is into a battery.
We force charge into them. Its why every one has a maximum charging current specification.
John Frum
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Current flow is about resistance and potential difference(voltage).
Forcing charge means increasing the potential difference between the charge source and the battery.
If the charge source and the battery are the same voltage no current will flow even if they were connected with a super conductor.
The way a charge source limits current is by adjusting the potential difference downward.
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The easy way out is to ensure you have devices that would serve as opportunistic loads...else the Charge Controller will try to push out as many Amps as possible while the battery will try its best to resist based on its internal resistance. Also if your battery is minimally discharged, its internal resistance is higher at this point and the its easier for the charge controller to reduce the amount of current supplied. Therefore ensure you either have an opportunist load or high SOC; 80% is ideal.
@smoothJoey Yes, correct chemistry assertions aside, energy flows from high to low.
We cannot have flat tires sucking air from the compressors around here!
So, what a battery will accept based on its resistance and what it should accept as a matter of service life, manufacturer instructions and in the case of flooded batteries the freaking mess and constant maintenance in the battery cabinet.
So when the charger raises voltage current flows to the lower potential of the battery, yes but opening the floodgate will reduce battery service life amd increase maintenance amd replacement costs.
Set your controller within battery manufacturer guidelines no matter the theory being used to argue the physics of charging.
Excessive loss of water, drying or shrinking of electrolyte pastes, shorts, overheating and erosion of plates can result from charging at too high current levels but in the case of fla, cooks off water and spittles electrolyte all over the cables, terminals battery tops and cabinet.
My batteries are going on 4 years in service. Never wash them just dab when done watering two to three times a year.
No, spittle. No dried electrolyte, no terminal or cable/lug corrosion. No neutralizer.
I have better images somewhere. The big battleship mostrosity is what a company was producing at way too high costs, dont know how they swung those deals. They never heard of an RE loadcenter or e-panel! Some of the disconnects are 300$ where a breaker would work fine! Wire amd cable management, cable size and terminatinations caca as with the architecture.
Either way it was a long line of rehab for their old systems. If you zoom in you can see the neutralizer everywhere. Inside the battery boxes was horror.
We cannot have flat tires sucking air from the compressors around here!
So, what a battery will accept based on its resistance and what it should accept as a matter of service life, manufacturer instructions and in the case of flooded batteries the freaking mess and constant maintenance in the battery cabinet.
So when the charger raises voltage current flows to the lower potential of the battery, yes but opening the floodgate will reduce battery service life amd increase maintenance amd replacement costs.
Set your controller within battery manufacturer guidelines no matter the theory being used to argue the physics of charging.
Excessive loss of water, drying or shrinking of electrolyte pastes, shorts, overheating and erosion of plates can result from charging at too high current levels but in the case of fla, cooks off water and spittles electrolyte all over the cables, terminals battery tops and cabinet.
My batteries are going on 4 years in service. Never wash them just dab when done watering two to three times a year.
No, spittle. No dried electrolyte, no terminal or cable/lug corrosion. No neutralizer.
I have better images somewhere. The big battleship mostrosity is what a company was producing at way too high costs, dont know how they swung those deals. They never heard of an RE loadcenter or e-panel! Some of the disconnects are 300$ where a breaker would work fine! Wire amd cable management, cable size and terminatinations caca as with the architecture.
Either way it was a long line of rehab for their old systems. If you zoom in you can see the neutralizer everywhere. Inside the battery boxes was horror.
Nope...
Not if the charge controller has a voltage setting.
It will PROVIDE as much current as the battery will DRAW at a specific voltage, but there is no FORCING current into the battery, UNLESS voltage exceeds the parameters.
yes, bad controllers like PWM cheapo, or shop battery chargers, will up the voltage to 15 or 18V to push watts in faster... and that is bad.
Im aware of the direction of demand issue. And the correction is noted for further appeasements.
What i am attempting to illustrate is that you need to limit current to the battery, the battery is not self limiting to avoid destructive charging..... the control needs to be set to do that.
Now im going to let my tires suck the compressor dry! I kid.
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