Charge controllers in parallel for both charging AND load

[James259]

Hi,

I know the question about putting charge controllers in parallel has been asked and answered a lot, but the threads I have found all talk about doing it for charging only and any diagrams I have seen show only one pair of load terminals connected. I am interested in also connecting together the load terminals to increase maximum output current for my load.

First of all, I am on a budget so going out and buying a big fancy charge controller may be an obvious answer, but I am hoping for a more cost efficient method. (I am also hoping to just add in more controllers as I get more panels, which will be over a long period of time)

I currently have a couple of 12v batteries. (2 brand new 120Ah deep cycle, received today)
I have a single 200W 24v panel and hopefully will soon be getting a 250W 24v panel to go with it.

I have a cheap charge controller. (its called SOLAR30, ebay special)

I recently got my hands on an 800w 12v inverter.

My charge controller has a maximum rating of 30Amps.
My load that I want to run occasionally is 500watts. I make that approximately 42 Amps.
My general load the rest of the time (maybe an hour or two per day) varies between about 20w and 80w. (about 1.5A to 6.5A)


What I was hoping to do is get another identical (well, same brand/model) 30A charge controller and run it in parallel with the other. (except for the panel connection)

My batteries are in parallel, so running at 12v.

From what I have read, I have a pretty decent chance of being able to attach a single panel to each controller and connect the batteries to both controllers at the same time by simply connecting the positive terminals together and negative terminals together. (Actually, trying to make the cable length from each controller to battery as close as possible, not simply daisy chaining them, to minimize voltage difference the two controllers see.) I understand that the controllers will probably come on/off at slightly different times and there is a chance that one may make the other think the battery is charged so it doesn't activate. For that side of things I will just try it and see. From what I have read it sounds like a lot of people have had a fair amount of success with that configuration.

My question is can I do with the load side what I plan to do with the batteries? Connect together the two positive terminals and then the two negative terminals and attach my 42A load? Is this something that can work or will the whole thing just blow up in my face? I am hoping that both controllers will simply share the load and allow me to run maybe 50A for a short period if I needed to.

I do understand that at 50A my batteries are gonna be reaching 50% in around 2 hours. I only want to use this load for maybe 30 minutes and probably only once a week. (maybe twice) I also hope to add more panels and more batteries later. (and possibly a 3rd controller)

Can anyone share any experience with this?


I only recently bought the inverter, which is rated at 12v only.
My controllers are rated 12v/24v. In hindsight I would obviously have connected the batteries in series to run at 24v and get a 24v invertor, cutting my current demand in half. Isn't hindsight a wonderful thing. :/
Unfortunately, I purchased the invertor a few weeks ago when I was running on a single dying 12v car battery. I since replaced that with 2 new ones.

I very much appreciate the time anyone spends trying to help me out.

[Sunking]

Man we gotta a lot of work to do here with you. Not sure I want to walk you through it as you have little knowledge on electrical fundamentals. Only so much we can do here. . First things first. Your charge controller current rating has nothing what so ever to do with you load current.

All the charge current rating on a controller means is how much charge current (Maximum) the controller can safely pass from the panels to the batteries. Has nothing to do with how much current the batteries can supply to a load.

The real issue for you is your battery capacity and expected load. Can it do the job. For a 500 watt load at 12 volts you are going to need at least a 400 AH battery to deliver 500 watts for any length of time.

[LETitROLL]

Hi,


I recently got my hands on an 800w 12v inverter.

My charge controller has a maximum rating of 30Amps.
My load that I want to run occasionally is 500watts. I make that approximately 42 Amps.
My general load the rest of the time (maybe an hour or two per day) varies between about 20w and 80w. (about 1.5A to 6.5A)

From the way you explain it, I think you maybe looking at the Load hookups on your charge controller wrong. They do say LOAD, but especially on inexpensive charge controller you "DO NOT" want to hook up any sizable load (over 10a) directly to your Controller. The large loads you are describing 30A to 50A would normally be hooked directly to your battery bank, and any inverter also "DO NOT" hook to CC, only direct to your battery bank. Now your panels should not produce more than about 15A combined, so your 30A CC is enough, if you tried to run a 50A load to CC you would need 2 as you described, but you do not want to hook it up that way anyhow, so you just saved buying another CC. With your panels already 24v, your CC okay for 24v, and your 2 batts. in series (better) are 24v, you already have a complete 24v system (minus the inverter), you may have to look into trading/upgrading the inverter to 24v, the advantages are significant.

[Mike90250]

here's the simple way for me to say NO, it won't work that way.


Take 2 watches. Set them to the same time. Check the next day, they are different !

The hope of synchronizing 2 or more controllers to manage parallel LOAD connections, is vanishingly small. Zero.

[James259]

Thank you all for your responses.

Sunking: Understood. After reading your comment I did some reading of the sticky threads on here and followed some calculations. For my peak expected usage (one or two days per week) it came out at 306.25Ah so my current 240Ah would be inadequate based on that, as you suggested. I will add 2 additional batteries near the top of my wish list. (I know 1 120Ah would bring me close enough but I will buy in pairs so I can switch to 24v configuration if/when I can afford to replace the inverter.)

LETitROLL: Interestingly, my original plan was to hook up directly to the battery for load and ignore the load terminals on the charge controller. However, this does not work. I can connect up that way and draw my load no problem. However, in the daytime when the panels are supplying power - if I run a load from the batteries directly, the charge controller appears to detect the falling battery voltage when its expecting it to rise. In response to this it enters a kind of panic mode (manual calls it "Abnormal Operation") and suspends any charging until I intervene with the buttons on the controller. If I connect my load to the load terminals on the controller then it works fine. The controller keeps track of Ah in and out (I can browse that info on the LCD) so I guess it knows when there is a load present if connected to the terminals and so expects the battery voltage to drop.

Mike90250: I am not sure that I understand what you are describing with the watches. You could probably tell me in more technical terms if it was easier. I did study electronics for about 5 years, albeit a long time ago, so I will quite probably have half a chance of understanding. I already know that on the charging side there can be issues with the two controllers seeing slightly different battery voltages (component variations, differing cable resistance/length, etc) and also the issue that controllers can switch on/start charging at slightly different times, which can result in the second controller never turning on because the battery voltage is already too high if the second controller takes too long to kick in after the first one. From what I have read the issues in doing this for charging are more of an annoyance (sub-optimal) than damaging though and quite a few ppl I have seen talk about it said it often works reasonably well - just depending on the controller. (Sounds like a pot luck thing)

The load side is obviously going to be different as it doesn't really do any PWM or anything to change the voltage around. I assume it just passes though, trips at peak current and has a mechanism (diode, mosfet, etc) for preventing reverse current flowing from load side to battery. I was just hoping someone had actually tried this sort of thing before.

Is connecting directly to the battery for load a common thing then? Strange that my charge controller kind of actively prevents it. I didn't buy the cheapest, but it is cheap. I chose this one because it has LCD to give statistics and show whats going on. Maybe I should have just gone for those really cheap tiny boxes?

If anyone else has anything to add then please do. Maybe I will just have to give up for now and save up for a long time for an 80A controller, or something that doesn't have a hissy fit when I take load directly from the batteries.

Thank you guys for your input. Very much appreciated.

[Sunking]

Sunking: Understood. After reading your comment I did some reading of the sticky threads on here and followed some calculations. For my peak expected usage (one or two days per week) it came out at 306.25Ah so my current 240Ah would be inadequate based on that, as you suggested. I will add 2 additional batteries near the top of my wish list. (I know 1 120Ah would bring me close enough but I will buy in pairs so I can switch to 24v configuration if/when I can afford to replace the inverter.)

James there is another catch FLA with batteries. Not only are there limits of how much current they can supply to a load, they also have some minimum input requirements for charge current to prevent the electrolyte stratifying. Generically speaking the minimum is C/12 where C = the battery Amp Hour Capacity, and the number is charge/discharge rate in Hours. So for example if you have a 120 AH battery the minimum charge current is 120 AH / 12 H = 10 Amps. So if you are using a PWM controller with 18 volt battery panels require 180 watts of panels, or if you use MPPT controller requires 120 watts minimum.

As you can see you just cannot arbitrarily change one component without affecting another component. Everything has to be made to work and support each other. It also makes things real easy for us to see problems instantly without any thought. Example let's say someone comes here and says: I have a 1000 watt 12 volt inverter, 12 volt 100 AH battery, 100 watt panel with 10 amp charge controller and the Inverter shuts off after a few minutes.

We know instantly what is wrong. We know a 1000 watt 12 volt Inverter requires 100 Amps of current. It takes a minimum 12 volt 800 AH battery to deliver 100 amps (C/8 maximum current) . A 800 AH battery requires 80 amps (C/10 sweat spot) of charge controller with 1000 watts of panels using MPPT, or 1500 watts with PWM. Take note that in most cases Inverter wattage roughly equal Panel wattage. When we see that balance upset we instantly know what is wrong.

So be careful, you cannopt just go change one thing without having to change the rest of the equipment. Battery systems do not lend themselves to growth very well.

[LETitROLL]

Is connecting directly to the battery for load a common thing then? Strange that my charge controller kind of actively prevents it

As far as I know, with cheap 30A and under PWM controllers it is highly common as they will often be damaged if you try and pull any large loads through them directly. You may want to do a few tests with that, use a couple of different smaller test loads, When you have a large load directly to your battery if it is near or over maximum normal discharge rate (about 1/8th of batt. A/H rating?) then of course battery voltage drops rapidly, maybe your controller sees that (externally) as a system problem and adjusts in response. I have hooked up both direct and through CC (only small loads) with a couple different controllers and no issues. Those load terminals are usually switched for adjustable dusk/dawn lighting control, etc. and more for help with small load control/management on the units I have tested.

[Mike90250]

As far as I know, with cheap 30A and under PWM controllers it is highly common as they will often be damaged if you try and pull any large loads through them directly. You may want to do a few tests with that, use a couple of different smaller test loads, W

Or you can read the manual and spare yourself the trouble of possibly burning out a controller.

re: Watches. They will drift with time, and give you 2 different readings. Same with multiple controllers. This is where precision counts, and is absent. Even just being different .1 volt, will cause a problem, one shuts off, the other is forced to take the full load.

Some controllers can be programmed to sync their charge voltages, but not the load cut-offs.

[Bucho]

As far as I know, with cheap 30A and under PWM controllers it is highly common as they will often be damaged if you try and pull any large loads through them directly.

You should be able to use a 30A CC for a 30A load. You should not be able to use it for a load larger than 30A.

[LETitROLL]

You should be able to use a 30A CC for a 30A load. You should not be able to use it for a load larger than 30A.

On most charge controllers that may be correct, but on at least a few (mostly inexpensive ones) it may not be true, I have been told by Renogy, especially on loads other than simple lighting, that I should not exceed 20 ~ 25a on the load output of their basic 30a PWM controller. Some loads (like inverters) of course will draw more for a brief moment to charge Caps., or motors that need startup surge, and it seems one may want to leave a little headroom.

[Bala]

I have dual charge controllers but have another unit that is connected in the system so they work together.

My system is 24V, and I have 12V, 24V and 240VAC items running off my load terminals with different cut in out times and voltages via relays.

My load terminals on the CC are only 7 amps, but all that is connected to the load terminals are the coils of the relays so the load terminal only has milliamps of current.

My total load is based on relay size, which can be as much as you want,

[SunEagle]

I have dual charge controllers but have another unit that is connected in the system so they work together.

My system is 24V, and I have 12V, 24V and 240VAC items running off my load terminals with different cut in out times and voltages via relays.

My load terminals on the CC are only 7 amps, but all that is connected to the load terminals are the coils of the relays so the load terminal only has milliamps of current.

My total load is based on relay size, which can be as much as you want,

Using low amp draw relays connected to the Load Terminals is a pretty good idea. I would still add a fuse a head of those relays to protect the CC in case one of them shorts out.

[Bala]

Using low amp draw relays connected to the Load Terminals is a pretty good idea. I would still add a fuse a head of those relays to protect the CC in case one of them shorts out.

Everything is fused.

The load terminal on the CC is rated at 7amp and I have a 1amp fuse inline.

[SunEagle]

Everything is fused.

The load terminal on the CC is rated at 7amp and I have a 1amp fuse inline.

Good job.