MPPT Charge Controller Adjustable Voltage / Parallel?

[mikes]

Ok, so I have two questions that I'm hoping someone can help me out with.

1) If I buy 2x 20 Amp charge controllers, can I connect the output of them in parallel to the same bank of batteries to charge those batteries at a maximum of 40amp? Each charge controller would have it's own PV input.

2) I'm trying to find a 24v MPPT charge controller that I can adjust the output voltage on so I can charge a Lithium Ion battery pack. Most of the ones I'm finding are preset for other battery chemistries. I need one that I can adjust to make sure each cell is getting the correct charge voltage (24v would be 4.2x7 or 29.4v). I have a cheap Chinese PWM charger that allows adjusting but would prefer MPPT for the obvious reasons.

Thank you very much!

[Logan005]

If you need a 40a CC, Get a good quality MPPT controller that does 40a or better. two MPPT CC's I am aware of that have fully adjustable operating parameters is OutBack and Midnight solar. I own an OB flex80, very nice CC for about 500 bucks. there are other brands, these are the ones I know.

[Amy@altE]

Midnite Solar's Kid charge controller has the ability to select the battery type for predefined settings, they include Lithium as one of the choices. If their settings aren't what you need, you can select Custom and enter your own settings. The Kid is a 30A MPPT charge controller that also has the ability to talk to each other when 2 are installed in parallel, ensuring they are truly working together instead of potentially conflicting. Sounds like exactly what you are looking for to me.

[Sunking]

Tightwad, cough up some money for a good controller. Your first challenge is using Lithium Cobalt cells requiring 4.2 vpc. That voltage does not play well with 12, 24, 36, and 48 volt systems. At 3S for 12 volts is 12.6 volts charge and operates at 10.8 volts. 12 volt equipment does not like operation at 10.8 volts and shuts off at 10.5 volts. You could use 4S, but that puts charge voltage up at 16.8 volts out of range for most charge controllers. Most 12 volt equipment will not play well when charging at 16.8 volts. Makes no difference at 24 volts, just double the numbers.

You should be using LiFeP04 cells which use 3.6 vpc charging and 3.2 operation which is a good match for 12, 24, 36, and 48 volt systems. That puts charge voltage at 14.4, 28.8, 43.2 and 57.6 volts which is perfect even for cheap charge controllers with no adjustable voltages as those are perfect voltages and compatible with all 12, 24, and 48 volt battery equipment. Operating voltage is at 12.8, 25.6, and 51.2 which is perfect match either charging or operating.

[mikes]

Sunking, I believe the post is specifically asking about a charger to charge Lithium Ion cells. Not about LiFePO4, Cobalt, Tightwads, etc. Thank you for your comments but it does not help either of my questions. Furthermore, I am not sure why you are calling me a tightwad. Nothing in my original post suggested I was looking for cheap.

Thanks Amy@altE & Logan005, I'll check them out.

[Sunking]

Sunking, I believe the post is specifically asking about a charger to charge Lithium Ion cells. Not about LiFePO4, Cobalt, Tightwads, etc.

BS.

First 4.2 volts per cell is Lithium Cobalt cells. LiFeP04 (aka LFP) is 3.6 volts per cell. So yes you did say specifically Lithium Cobalt. You just do not know what the heck you are talking about. Lithium charge voltages range from 3.1 to 4.4 volts per cell. 4.2 volts per cell is specifically Lithium Cobalt. 3.6 is specifically LiFeP04 and the only cell compatible with off the shelf solar equipment you can buy. You are just making things more difficult if not impossible using Lithium Cobalt which is incompatible with Solar. Use LFP and you can even use Cheap Chi-Com with fixed outputs or anything else with adjustable outputs you want. That is the Best advice you going to get.

Yes you are a tightwad and is exactly what Amy and Logan are telling you. They are telling you to quit thinking about buying cheap POS Chi-Com controllers with fixed outputs. They are telling you to buy a single controller of 30 to 40 amps from a reputable company that will cost you 3 to 6 times more than cheap Chi-Com POS equipment. Go price out the Midnite Solar Kid controller. It is $300 to $400 for a 30 amp controller. Expect to pay $100 per 10 amps of controller

Am I making myself perfectly clear?

[mikes]

BS.

First 4.2 volts per cell is Cobalt cells. LiFeP04 is 3.6 volts per cell. So yes you did say specifically Lithium Cobalt. You just do not know what the heck you are talking about. Lithium chare voltages rangge from 3.1 ro 4.4 volts per cell. 4,2 is specifically Lithium Cobalt. 3.6 is specifically LiFeP04 and the only cell compatible with off the shelf solar equipment you can buy.

Yes you are a tightwad and is exactly what Amy and Logan are telling you. They are telling you to quit thinking about buying cheap POS Chi-Com controllers with fixed outputs. They are telling you to buy a single controller of 30 to 40 amps from a reputable company that will cost you 3 to 6 times more than cheap Chi-Com POS equipment. Go price out the Midnite Solar Kid controller. It is $300 to $400 for a 30 amp controller.

Am I making myself perfectly clear?

I am aware that a single controller is better. I am asking for proof of concept - does it work. I am not saying that I'm going to buy 2x 20amp controllers. That would be retarded. I know exactly what I'm talking about. I'm talking about charging Lithium Ion cells. I'm not going to go in to any further details because you're just going to come at me with more arrogant responses on how I'm doing it "wrong" in your eyes. If you don't have anything useful to add to this conversation, please refrain from posting and acting like an asshole to me. It is rude and disrespectful.

Am I making myself perfectly clear?

[Sunking]

I am aware that a single controller is better. I am asking for proof of concept - does it work.

Yes it is common to use two controllers on dedicated panels serving a common battery. However it is usually reserved with total charge current above 80 amps since 80 amps is the largest controllers you can buy, and use controllers with a communication link for Load Sharing. That is what they are made to do. No proof of concept involved, already on the market. But it will not be from any Chi-Com owned company making POS PWM controlers. It will be from companies like Midnite Solar, Morningstar, and Outback and none of those are inexpensive.

You can even use cheap controllers PWM or MPPT with fixed outputs. But what will happen is one controller will have a slightly higher voltage than the other and will dominate. Initially both will output full power, But when the battery nears full charge, the other will drop out. The voltage set point has to be within .01 volts. Even with adjustable outputs is impossible to balance without a Comm Link.

Lastly again use the right Lithium Cell for Solar. Only LiFeP04 is comparable with off the shelf solar, and you can use any controller you want. Use anything else and you will likely fail. Even if you use Chi-Com chit you can make it work with LiFeP04 as the voltages are the same as Lead Acid. Use something else and it will be a loosing battle.

[jflorey2]

2) I'm trying to find a 24v MPPT charge controller that I can adjust the output voltage on so I can charge a Lithium Ion battery pack. Most of the ones I'm finding are preset for other battery chemistries. I need one that I can adjust to make sure each cell is getting the correct charge voltage (24v would be 4.2x7 or 29.4v).

I will second Amy's suggestion for the Midnite Kid. It's a great controller and is configurable to do what you want to do. As others have pointed out, it will be closer to 3.7 volts per cell for practical batteries (LiFePO4.)