Panel/array size vs battery bank & daytime only loads?

[Sunking]

Isn't there an MPPT controller out there, which can be set to limit the output current (like my grid tie)? Bruce Roe

Yes but why? Charge current is determined by panel wattage and battery voltage selection. All the controller does is regulate voltage.

However there are some Controllers that will allow you to limit charge current which is insane IMO. Example say you have 2000 watts of panels on a 24 volt battery. Max charge current is 80 amps, but you limit to say 50 amps. You just reduced panel wattage 1250 watts. That is nucking futs IMO and says you have a piss poor design.

To the OP go back and read my reply in post 12. You can make this work if you use the right Inverter and battery type within your budget. Hopefully by now you have figured out your application is not a good fit for solar. You would be better off using a generator for the tools and use solar for the small stuff.

[bcroe]

I don't think its such a bad idea. Sure its very convenient to limit max current by limiting panel wattage. It works
where the sun shines every day. But with frequent clouds, it is inadequate many, many days. Doubling up panels
will mean meeting needs many more days, and a current limiting MPPT will mean no additional problems
with batteries. Bruce Roe

[sensij]

I don't think its such a bad idea. Sure its very convenient to limit max current by limiting panel wattage. It works
where the sun shines every day. But with frequent clouds, it is inadequate many, many days. Doubling up panels
will mean meeting needs many more days, and a current limiting MPPT will mean no additional problems
with batteries. Bruce Roe

Yeah, I agree. Where the OP is going wrong is in choosing a 60 A charge controller on a 200 Ah bank. Why spend money on a big CC if it is just going to be throttled back? If a smaller charge controller (say, 30 A) is chosen that is better matched for the battery, over-paneling the system for heavy daytime use (when the sun is available) is fine if night-time consumption is served by that smaller battery.

[Sunking]

Yeah, I agree

I think you are missing a big point. He wants to use panel power during mid day to supplement battery power to run a brute of a 3000 Watt Inverter. Choke or limit panel current with an undersized battery is asking for false trips.Last thing you want to do is limit power on an already limited soft source.

This can be done and is done routinely for a different application we use in the USN. In a submarine there comes a time when the Captain says give her all shes got Scotty to make the sub fly. The nuke has limited power, and when you need to sub to fly, you bring a 500 volt 10,000 AH battery on-line to supplement the nuke. Do that and the sub flies real damn fast, but only for an unspecified amount of distance.

[sensij]

I think you are missing a big point. He wants to use panel power during mid day to supplement battery power to run a brute of a 3000 Watt Inverter. Choke or limit panel current with an undersized battery is asking for false trips.Last thing you want to do is limit power on an already limited soft source.

This can be done and is done routinely for a different application we use in the USN. In a submarine there comes a time when the Captain says give her all shes got Scotty to make the sub fly. The nuke has limited power, and when you need to sub to fly, you bring a 500 volt 10,000 AH battery on-line to supplement the nuke. Do that and the sub flies real damn fast, but only for an unspecified amount of distance.

There are times when over-paneling is more cost-effective than building the whole system up to be balanced. You're right, though, I didn't focus too closely on the actual loads the OP intends to run during the day. If the panels can chip in an extra 700 W that the batteries don't have to supply, the chances of getting a power tool to start up without a false trip are better, but the risk of a trip still exists. There is a safe way to over-panel for daytime loads, but it tends to be better suited for lower, continuous loads, and doesn't add much to the power capability of the system.

[Wy_White_Wolf]

I don't think its such a bad idea. Sure its very convenient to limit max current by limiting panel wattage. It works
where the sun shines every day. But with frequent clouds, it is inadequate many, many days. Doubling up panels
will mean meeting needs many more days, and a current limiting MPPT will mean no additional problems
with batteries. Bruce Roe

If you limit current from the array to the battery bank how does the extra current reach the inverter?

Limiting the current just defeats the purpose of an oversize array.

WWW

[Sunking]

If you limit current from the array to the battery bank how does the extra current reach the inverter?

Limiting the current just defeats the purpose of an oversize array.

WWW

That is what they are missing.

[Amy@altE]

Just to mix things up a little, oversizing the array and limiting the charge controller current output, like with a Morningstarr MPPT charge controller, will prevent the warned of boom mid-day, and will allow the solar array to provide more power earlier and later in the day. So while it may clip the output mid-day, you might even it out with more energy generated through the off-peak time. Also, not sure if anyone brought it up, but if these panels are mounted on a bus roof, the output will be seriously derated due to lack of tilt angle, especially in the winter. So an oversized array may be helpful.

[bcroe]

If you limit current from the array to the battery bank how does the
extra current reach the inverter. Limiting the current just defeats the purpose of an oversize array.
WWW

It does seem limiting charge current takes care of the batteries, but NOT the need for a lot of extra load
power. Can't a charge controller just limit as battery voltage rises, and add current as the load pulls
the voltage down (like most DC systems)?

I'm inclined to agree with SunKing that just using a generator is the simple solution. Another way is to
go to battery powered tools; direct battery can deal with surges, and a controller monitoring voltage would
start dumping in extra power when tools are turned on.

Part of the issue is not understanding the load in detail. Not being plugged into a nuke, power has to be
measured off carefully. An AC motor needs a big surge from a stiff source, but then drain will follow the
loading. Here most tools run a VERY SMALL percentage of the time, even in active service. That is exactly
the wrong type of load for solar, that delivers modest power all mid day. We fix it of course with a battery,
but that means the battery must deal with the surges, if the solar can deal with the average. So the
battery and SunKings surge rated inverter will set what is possible on an AC system, adding panels for
surge is VERY inefficient. Bruce Roe

[jflorey2]

Isn't there an MPPT controller out there, which can be set to limit the output current (like my grid tie)? Bruce Roe

Yes. However, what the OP wants is an MPPT controller that will limit CHARGE current but not OUTPUT current. That way he does not overstress his batteries, but has all that power available for his tools. It would require relocating the output current sensor to the battery, rather than leaving it inside the charge controller. I don't know of any charge controllers that allow that.

[Sunking]

It does seem limiting charge current takes care of the batteries, but NOT the need for a lot of extra load
power. Can't a charge controller just limit as battery voltage rises, and add current as the load pulls
the voltage down (like most DC systems)?

No that is my point, the load is IR. Increase current into a resistance, and voltage goes up. You cannot have one without the other. A Charge Controller or any battery charger is just a DC power Supply with current limiter and voltage regulator. It can supply X amount of current up to a specified voltage. Say 10 amps at 12 volts into a 1.2 ohm load. So what happens when the load goes to 1 Ohm? Simple the current limiter folds back voltage to 10 volts to limit current to 10 amps. That is called the Bulk aka Constant Current Mode.

Part of the issue is not understanding the load in detail. Not being plugged into a nuke, power has to be
measured off carefully. An AC motor needs a big surge from a stiff source, but then drain will follow the
loading. Here most tools run a VERY SMALL percentage of the time, even in active service. That is exactly
the wrong type of load for solar, that delivers modest power all mid day. We fix it of course with a battery,
but that means the battery must deal with the surges, if the solar can deal with the average. So the
battery and SunKings surge rated inverter will set what is possible on an AC system, adding panels for
surge is VERY inefficient. Bruce Roe

Bruce technically you are talking about a Stiff Source vs a Soft Source. POCO and Generators are Stiff Sources of practically speaking unlimited power. Solar is a Soft Source of unknown power at any given time. At best it might be 1000 watts on a 1200 watt system at solar noon or 120 watts at solar noon. Completely unknown and unreliable. The only way to stiffen it up is with batteries and even batteries are soft sources. A 100 AH battery is only good for 10 to 20 amps for relatively short period of time before the voltage starts to fall.

Th eOP like so many who come here asking for the impossible. His application is not a good candidate for solar. He may only need 1Kwhj a day and under normal circumstances would only need a 12 volt 400 AH battery. But that 3 Kva motor load eliminates that. It dictates a much larger battery which he cannot afford and wants to make up with solar which would harm a smaller battery. He cannot have his cake and eat it to.

I do know one work around, but not for this person. Actually simple. But if he cannot afford the proper size FLA or AGM battery, he damn sure cannot afford LFP. Nor does he have the skills to operate a LFP battery.

A generator is the right answer.. Use the solar for the small stuff. If it were me I would just use a generator, charger, and small battery for small stuff. Use the generator to charge the batteries and charge batteries. To hell with solar and the expense. He could work day and night in any weather. That is what anyone would do who has hungry mouths to feed.

[badley]

all that needs to be done really is switch off panels on a normal basis so only enough is 'on' to keep the batts maintained and dont over-current them, thats hella bad for them .. batteries are THE problem in any system, keeping a large bank balanced regardless of setup is a real challenge and in most cases im sure leads to early failures .. more panel is good, during the day, your in float, bang on the 'other' 12 panels .. a properly set up 12 system works fine, mine does it doesnt 'dim' when i put a heavy load on, mppt is hype, imo so is high voltage setups - its for whiners with 4 panels and 50 batteries theyre in the process of destroying .. when they go, and they will if they arnt religiously monitored and maintained .. that will be the end of their little solar experiment ..

[Sunking]

all that needs to be done really is switch off panels on a normal basis so only enough is 'on' to keep the batts maintained and dont over-current them,.

That is not required. A charged up battery does not charge or accept current. The battery voltage will be equal to the charger voltage, thus no current.

[Mike90250]

...., mppt is hype, imo so is high voltage setups......

Well, I disagree with your opinion. Many factors get decided when designing a system. One is the decision from PWM to MPPT, and another is efficiency and Voltage

[jflorey2]

all that needs to be done really is switch off panels on a normal basis so only enough is 'on' to keep the batts maintained and dont over-current them

You can do exactly the same thing with a charge controller. They let you adjust the output current as well - without switches and relays.

a properly set up 12 system works fine, mine does it doesnt 'dim' when i put a heavy load on

Sure, at low powers. Inverter AC systems don't "dim" as long as AC side wiring is OK - they provide 120 volts until they don't anymore due to high IR drops.

At higher powers higher voltages make more sense.

mppt is hype, imo so is high voltage setups - its for whiners with 4 panels and 50 batteries theyre in the process of destroying .. when they go, and they will if they arnt religiously monitored and maintained .. that will be the end of their little solar experiment ..

You have no clue what you are talking about.