Cheap MPPT Controllers for casual use

[SolarCurious]

While I do not have first hand experience with one of those charge controllers I wouldn't say it was unsafe just not efficient.

With an MPPT charge controller the formula is Watts in = Watts out. So if you have 500 watts charging a 12volt battery the amount of amps the CC can produce = 500w / 12v = 41.7amps. A PWM type charger is Amps in = Amps out so those 500 watts will only get you about 30amps at best. Having more charging amps with an MPPT type charger will allow you to maintain a larger battery system and is more efficient then a PWM cc.

Back to your decision to have an battery powered emergency backup system. The issue is that even if you do not use those batteries much they still reduce in life. You have to keep them charged and need to at least cycle them every once and a while. Just letting them sit around does not make them happy. It will be more work just to baby sit your investment to they work when you need them.

Next thing to consider is the amount of battery (and the cost) needed to run that fridge and AC unit. Those type of appliances are big watt hour users which will require a pretty big battery bank. Now you have this very expensive solar panel/battery system that is not used much but still needs to be check, charged and maintained with the main reason to be used during a power outage.

If you do not have many power outages then using a standby generator will be much less expensive to have as your backup power source then a very large battery system.

To me it is an easy decision to use a generator as my emergency power supply then to have a bunch of solar panels stored away and a battery system that needs to be baby sat so it will work when I need it.

Yes, I am use PWM controller. So it seems I will be right at the limit for Amps. Maybe I need a 40 amp controller after all for safety margin?
The batteries are being used in other places while not being used for solar. ie...boat and van
I can usually get 4 to 5 years out of these batteries.

I also have a Honda inverter generator. Problem is, after about two weeks (if gasoline does not become available) you're out of luck. That happened many years ago.
So the solar is there for situations where power is out long enough for my gasoline reserves to run out. It has happened where I live.

My understanding is that generally speaking, Grid power is cheaper than solar power. So I will use grid power whenever possible.

Thanks

[SolarCurious]

One thing that does concern me with the cheap charge controllers is heat dissipation.

I notice that most of the better quality charge controller have significant means of dissipating heat via fins. Some have fans.

I'm not sure how the small, cheap charge controllers deal with the heat issue.

[jimindenver]

I have to agree with the concept of using a back up system. In this case there is not enough solar o handle enough battery to run the items you are looking to run.

Now if you had more battery I could see setting up a small functioning system as a hobby and learning project OR greatly scale back what you expect to run while using the gear as a back up system.

[SunEagle]

Yes, I am use PWM controller. So it seems I will be right at the limit for Amps. Maybe I need a 40 amp controller after all for safety margin?
The batteries are being used in other places while not being used for solar. ie...boat and van
I can usually get 4 to 5 years out of these batteries.

I also have a Honda inverter generator. Problem is, after about two weeks (if gasoline does not become available) you're out of luck. That happened many years ago.
So the solar is there for situations where power is out long enough for my gasoline reserves to run out. It has happened where I live.

My understanding is that generally speaking, Grid power is cheaper than solar power. So I will use grid power whenever possible.

Thanks

I understand where you are coming from. I have a few emergency backup power sources that I have acquired over a period of years mainly due to the possibility of power outages from hurricanes.

Those "backup" systems are; 5500watt & 1800watt gas generators, 3250watt LNG generator and a small solar battery system similar to what you are describing. I built this system a couple of years ago and like you have my panels nicely stored and my batteries (AGM type) being monitored and maintained.

I spent about $2500 on that system and it can safely get me about 600 watt hours a day which is a pretty small load at a high expense. Now that I better understand the cost and labor to build a solar battery "backup" system I would have gone with a whole house 10kw LNG generator with a 100 gal tank. That would get me about a weeks worth of power for just about everything in the house. I can't power even half of my loads even using all of those smaller generators and the battery system.

So take it from someone that made the mistake of thinking I can "cheaply" build a solar battery system for power outages only to find out it costs a lot more than what I thought and provides a lot less power than what I need.

[paulcheung]

One thing that does concern me with the cheap charge controllers is heat dissipation.

I notice that most of the better quality charge controller have significant means of dissipating heat via fins. Some have fans.

I'm not sure how the small, cheap charge controllers deal with the heat issue.

To my understanding that the PWM controller do not convert the high voltage to low voltage, it simple regulate the voltage , on the other hand the MPPT controller covert the high voltage low amps input to lower voltage higher amps output, that conversion create a lot of heat, hence the fins and fans .

[jimindenver]

You could use the system as you plan as a back up but for some lights, a fan, to keep your cell phone or laptop charged up. Even the smallest 5000 btu window AC I know of using 465w and 3.9a at 120v/ 39a at 12v wouldn't run long on your two batteries. Possible with fully charged batteries and your panels tracking the sun, the system would offset some of the load but that would only get you a little more run time. Even a different 5000 BTU unit may take over 500w and 46a which would out pace my 720w system.

My small systems work because a RV uses relatively small amounts of power compared to a house. It's systems are 12v to start with and most of the heavy work is done via propane. The furnace is the heaviest load in the trailer at 8a intermittent. The highest load on the inverter is a 1375w microwave that may run 8 minutes cooking some taters. The TV/satellite system uses more over the long run but when the batteries are in float during the day, they don't see it as the solar cover most small loads without dropping the batteries voltage. Only the microwave, hair dryer, coffee pot and vacuum do that, and they don't run long enough to drain the bank.

[inetdog]

To my understanding that the PWM controller do not convert the high voltage to low voltage, it simple regulate the voltage , on the other hand the MPPT controller covert the high voltage low amps input to lower voltage higher amps output, that conversion create a lot of heat, hence the fins and fans .

The PWM controller does not even have to deal with the difference between panel Voc or Vmp and the needed battery voltage, since the panels are a current source and if you pull enough current from them the panel voltage itself will drop as low as the CC needs it to be. Hence no extra heat dissipation beyond the voltage drop under load across the switching elements. And that can be less than one volt without much difficultly.

[SolarCurious]

Well, I found a pretty good deal on a Xantrex 40C which should handle the 40 amps I felt was a safety margin so I bought this instead of the cheaper one on ebay.

C-60(new).jpg

[SolarCurious]

You could use the system as you plan as a back up but for some lights, a fan, to keep your cell phone or laptop charged up. Even the smallest 5000 btu window AC I know of using 465w and 3.9a at 120v/ 39a at 12v wouldn't run long on your two batteries. Possible with fully charged batteries and your panels tracking the sun, the system would offset some of the load but that would only get you a little more run time. Even a different 5000 BTU unit may take over 500w and 46a which would out pace my 720w system.

My small systems work because a RV uses relatively small amounts of power compared to a house. It's systems are 12v to start with and most of the heavy work is done via propane. The furnace is the heaviest load in the trailer at 8a intermittent. The highest load on the inverter is a 1375w microwave that may run 8 minutes cooking some taters. The TV/satellite system uses more over the long run but when the batteries are in float during the day, they don't see it as the solar cover most small loads without dropping the batteries voltage. Only the microwave, hair dryer, coffee pot and vacuum do that, and they don't run long enough to drain the bank.

By far the one most vital appliance I want to run would be the refrigerator and I have run it on just ONE of these batteries for 6 hours so at the very least, I have more than enough to run my most vital appliance. That will save some of my generator gas for powering the small window AC for the one room I decide to cool (bedroom, for sleeping).

The batteries run everything. The solar panels just feed the batteries as I see it.
I have two more AGM 100Ah batteries on hand that actually act as server backup batteries and are constantly maintained by an APC battery backup.
So, if there was an extended power outage, I actually have 4 batteries for a total of 460Ah at my disposal.

More than enough to run a fridge and LED lighting.

Plus, I went ahead and purchased another 100watt panel so now I have 600watts and 36 amps (PWM)

[paulcheung]

By far the one most vital appliance I want to run would be the refrigerator and I have run it on just ONE of these batteries for 6 hours so at the very least, I have more than enough to run my most vital appliance. That will save some of my generator gas for powering the small window AC for the one room I decide to cool (bedroom, for sleeping).

The batteries run everything. The solar panels just feed the batteries as I see it.
I have two more AGM 100Ah batteries on hand that actually act as server backup batteries and are constantly maintained by an APC battery backup.
So, if there was an extended power outage, I actually have 4 batteries for a total of 460Ah at my disposal.

More than enough to run a fridge and LED lighting.

Plus, I went ahead and purchased another 100watt panel so now I have 600watts and 36 amps (PWM)

How much you paid for the 100 watts panel? you can buy a Tracer 40amps MPPT charge controller for less than US$250 and the 5 panels will give you 40 amps.

[jimindenver]

So you will need to understand how much power the fridge uses constantly and at start up. I think you will find that one 130 ah battery with 65 ah available will hard pressed to run a residential fridge for 6 hours. When you put a big load on a inverter, the bank that powers it drops voltage under load. as soon as the load ends the voltage shoots back up but the inverter sees the voltage under load and will shut down when it gets low enough. So you don't even really have 65 ah available in that situation. The two batteries combined will have abetter chance but it depends on your fridge.

As far as using the solar to assist in running things. we don't have room for a big bank to power our 3000w PSW inverter. On its own our 8-D can run the micro pulling 1375w for a few minutes before the voltage sag is too much. With the 490w solar it can nuke a few taters for 10 minutes and the sag doesn't get below 12v. Smaller things like the trailers furnace wont even bring the bank out of float as the solar just covers the load.

[Sunking]

Well, I found a pretty good deal on a Xantrex 40C which should handle the 40 amps I felt was a safety margin so I bought this instead of the cheaper one on ebay.

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Even if it is free is not worth the cost. It is PWM. It will rob you blind and you will not even know it.

[Sunking]

Plus, I went ahead and purchased another 100watt panel so now I have 600watts and 36 amps (PWM)

You may think you have 600 watts, but no where close because you have a thief in your system, a PWM controller. 600 watts should give you 50 amps.

[SolarCurious]

Even if it is free is not worth the cost. It is PWM. It will rob you blind and you will not even know it.

So why do they even bother manufacturing PWM controllers?

[russ]

So why do they even bother manufacturing PWM controllers?

Suckers will buy them.