Low battery disconnect + fall back charger?

[toothy]

Hello Weston

I get it.  Build what you want and enjoy it.

Here is my probably incorrect idea, shoot holes in it at will, use a standard off grid inverter and treat the grid as your generator input.

Use the inverters automatic generator start (AGS) to close a relay, when the inverter sees power on the AC side it will charge just like it would from a generator and stop/open the relay when charged.

Have fun
Wade

[vtmaps]

Weston, sorry for the unhelpful comments... you were quite vague in your requirements for equipment and motivations for solar.   Solar can be very disappointing if your expectations are not realistic, and I was probing to find out just what you expected from a system, and why. 

Use the inverters automatic generator start (AGS) to close a relay, when the inverter sees power on the AC side it will charge just like it would from a generator and stop/open the relay when charged.

I think this makes sense to accomplish your goals.  Buy a full featured off-grid inverter (magnum, outback, schneider) and use the AGS and the built-in transfer switch.

--vtMaps

[wbustraan]

I did call, actually. Unfortunately, my cell phone dropped the call and cut the discussion short. I decided that, since the engineers were busy people and my question is not urgent, it might be better to ask my question in message form, so that they might respond at their convenience, rather than tie up a phone line.

[wbustraan]

That's an interesting idea, I will probably look for that feature when I'm researching inverters.

The way I see it, there are 4 points at which you can feed external power to a battery bank that's not getting enough solar input to match demand:

1. Input to the charge controller
This is wildly theoretical, but, with a bridge rectifier, you could take 110VAC from the grid and make it look like a 110VDC source. Switching would be controlled by the Classic's Low Bat Disc

• pro: The Classic stays in control of the charging
• con: This would likely mess with the MPP tracking

2. Input to the battery bank
This is the scenario I described above, with an external AC charger that is turned on by the Classic's Low Bat Disc

• con: Have to use a delay to prevent it from toggling on and off due to voltage readings on the bank bank terminals
• con: External charger may not charge as efficiently as a Classic

3. Input to the inverter
The scenario proposed by toothy and vtmaps, using the AGS to feed power from the grid into the inverter as if it were a generator.

• pro: More efficient, because the electricity is not being converted from AC to DC and back.
• pro: Does not draw power from the bank, allowing all incoming solar power to be put towards bringing the battery bank back up to an acceptable voltage.
• con: Does not charge the battery bank. I am assuming that, in this scenario, the Classic is still responsible for charging the bank and the inverter does not have charging features. Until the sun comes back out, the bank will stay in a low charge state. I don't know how long it can stay that way before sulfation starts becoming permanent. Perhaps it's long enough that it's not a concern?
• con: Requires a more expensive inverter with more features

4. Input to the electrical panel
An automated transfer switch is triggered by the Classic's Low Bat Disc condition, switching the electrical panel temporarily to grid power.

• pro: More efficient, because the electricity is not being converted from AC to DC and back.
• pro: Does not draw power from the bank, allowing all incoming solar power to be put towards bringing the battery bank back up to an acceptable voltage.
• con: Does not charge the battery bank. Until the sun comes back out, the bank will stay in a low charge state. I don't know how long it can stay that way before sulfation starts becoming permanent. Perhaps it's long enough that it's not a concern?
• con: There would probably be a momentary interruption in power when the transfer switch flips. Might be an issue for electronics (blinking 12:00)

[zoneblue]

With a hybrid inverter/charger you can use the inverters AC input to charge the batterys via the internal charger function.

But you are right , its always more efficient to use the AC direct, rather than charge batterys. 

[vtmaps]

3. Input to the inverter
The scenario proposed by toothy and vtmaps, using the AGS to feed power from the grid into the inverter as if it were a generator.

• pro: More efficient, because the electricity is not being converted from AC to DC and back.
• pro: Does not draw power from the bank, allowing all incoming solar power to be put towards bringing the battery bank back up to an acceptable voltage.
• con: Does not charge the battery bank. I am assuming that, in this scenario, the Classic is still responsible for charging the bank and the inverter does not have charging features. Until the sun comes back out, the bank will stay in a low charge state. I don't know how long it can stay that way before sulfation starts becoming permanent. Perhaps it's long enough that it's not a concern?
• con: Requires a more expensive inverter with more features

Wrong assumption.  Both Toothy and I mentioned previously that it does require an inverter/charger.  The inverter/chargers also have a built-in transfer switch.  You can program an inverter/charger to NOT charge the batteries if you wish, but it will still transfer the AC to the loads.

As for the inverter/charger being more expensive, I thought you made it clear that this system is about independence, not cost-effectiveness.

--vtMaps

[wbustraan]

Wrong assumption.  Both Toothy and I mentioned previously that it does require an inverter/charger.  The inverter/chargers also have a built-in transfer switch.  You can program an inverter/charger to NOT charge the batteries if you wish, but it will still transfer the AC to the loads.

I assumed, given that this is a MidNite Solar forum, that their product should be included in the design. Otherwise, tell me why you are hanging out on this forum attempting to persuade people to buy products that MidNite does not offer?

I know there are devices out there that are all-in-one charger/inverter/grid-tie/transfer-switch/slice/dice/make-julienne-fries kind of devices. I happen to like what I see in the Classic 150. I like the features and I like what I've seen so far of the company that makes it. I'm guessing that there are many people who have built successful battery banks with the Classic in just the scenarios I described.

The other things is that I don't know how those all-in-one devices scale. If I have a separate inverter and charge controller, and I want to add a wind turbine to an existing solar system, I'm pretty sure I know what to do: I can just buy another Classic 150, set them up to talk to each other, and leave the inverter as is. I don't know how this works with the systems you're describing.

As for the inverter/charger being more expensive, I thought you made it clear that this system is about independence, not cost-effectiveness.

You're being deliberately obtuse. Please stop; it's not constructive to the discussion. If you go back an read what I said, I said that cost-effectiveness is not my primary motivating factor; I did not say that it was not a factor at all. If money were no object, I certainly wouldn't be visiting this forum and trying to figure it out on my own; I'd find a professional, tell him what I wanted, and pay him to figure it out.

Of course cost should be included as a factor when comparing solutions. If you've got two systems that both meet the requirements equally and one is more expensive that the other, why would you choose the more expensive one?

[zoneblue]

This thread is getting out of hand.  Please understand that we are trying to help.

If you want to use a battery with the grid, the best way is a purpose built hybrid grid interactive backup inverter. They are expensive.

If you want to use a classic with the grid you have two options:

- classic plus iota type ac charger, using aux1
- classic plus ordinary inverter/charger, using AC in.

Either will work. In the former, the hold and delay settings on aux1 can be used to take care of the contention / chatter etc.
With the later the hybrid inverter, has various settings to determine how the grid support is used and provides its own independent charging system.

There is a thrid way but its not that recomended, get two classics, and feed the iota into the pv terminals on one of them (via a big power resister), and that way you would be able to use followme coordination. But you dont need coordination in the followme sense because both sources are not being used during the later charge stages only one at a time.

Good luck. You may also like to check out the NAWs forum.

[Westbranch]

VT and ZB, from the beginning,  the OP has a concept that he is unable or unwilling to state as we have questioned his 'plan'... 

IMHO he has now flamed us while we have patiently tried to discuss various options for him to achieve his goal....

Nuff Said!

[TomW]

Sorry to drift off topic, folks, but. Lets work the problem.

We all know it is hard to clearly describe some things even if you are well versed in the technology. Doubly so if it involves those who are not.

Might need to back this train up and get a fresh perspective on exactly what the thread opener wishes to achieve.

Frustrating on all sides but lets not get sidetracked on conjecture, please.

Anyway, its pretty clear (to me) that turn key options exist and I happen to have one myself but off the shelf solutions do not fit every need. More information is better than less and a clear goal definitely helps.

Thanks.

Tom

[wbustraan]

I appreciate your responses, zoneblue and TomW, they gave me some hope. I'll give it another shot at explaining my question better.

Here's the scenario: Imagine that you have

• 6 solar panels
• a Classic 150 charge controller
• an inverter (I have a Whistler 2500W inverter, but it won't do 220VAC, so it won't work. I haven't figured out what one to buy instead)
• and some number of deep cycle batteries (my father-in-law manufactures electric wheelchairs and has offered to give me a bunch of deep cycle batteries).

Those are the basic components to build an off-grid system, right?

So, let's say you hook it all up and it works great; the solar input is keeping up with the demand all summer long. Now, one cold winter day, a snowstorm dumps a foot of ice and snow on your solar panels. You estimate that it's going to take at least a week for you to get it fully cleared off. Over the course of that week, your battery bank starts slowly depleting, because your panels aren't generating any current. Finally, it hits a low threshold and everything shuts down. You're now sitting in the dark.

Question 1: How long can you let the battery bank sit in that low charge state before the sulfation starts to become permanent damage?

Going further, you realize that you've got an 110 VAC source available to you. Whether that's a generator, a grid hookup, or even a big long extension cord that goes over to the neighbor's house, let's just assume that it's 110 VAC and the available wattage can handle the load. For purposes of this discussion, I'll call it "generator".

One solution to getting yourself out of the dark would be to install a transfer switch and manually switch the electrical panel over to the generator source in an emergency like this. But, going back to Question 1, that would just run your house; it wouldn't charge the bank back up, so it would still be sitting at low charge for a while. Now, if I don't need to worry about sulfation for quite a while, then this is probably the simplest solution. Run the house off the generator until the panels start producing current again.

Going one step further from that solution, it occurred to me that I could use that generator power to also charge the battery bank up with some sort of AC charger. That would get the bank back out of the sulfation danger zone.

So far, in this scenario, it's all manual. I would have to keep checking the display on the Classic periodically and see where the levels are at. Once the bank was charged back up, I would then go pull the switch and switch it from generator back to battery bank. If I can't figure this out, at the very least, I'm pretty sure this manual method would work.

However, one thing that is neat about the Classic is that it has the two Aux contacts. So, I thought, what if, instead of doing this all manually, I let the Classic control the process using a relay and Aux 1. And that is the question I posted in my very first message. As I understand it, the state of Aux 1, when using Low Bat Disc, is determined by measuring the voltage of the battery bank.

Question 2: Am I correct in my understanding that, if an outside device, such as an AC charger, is applying voltage to the bank and the Classic attempts to measure the voltage, it will appear to the Classic that the bank is charged?

Now, as has been suggested, I could purchase an inverter that has the ability to perform the role of the AC charger in the above scenario, and charge the bank. However, (assuming the answer to Question 2 is yes) unless they have the ability to communicate, I still have the problem of two devices (Inverter and Classic) attempting to charge the same bank and interfering with each other.

[ClassicCrazy]

The inverter charger and Classic won't interfere with each other. They will charge to their programmed setpoints. If the inverter charger has charged the battery all the way then the Classic will just go into float soon. If the batteries were only charged about 80% with inverter charger the Classic would finish off the charge. Neither one is going to charge and will go to float once their setpoints are reached.

[ClassicCrazy]

If you get new batteries all the same date of manufacture you will be okay. If you get used batteries of different dates you may not find very good performance.  That being said I have a bunch of used AGM batteries on a 12v system but don't expect them to work to their rated capacity. But they work for the small loads I need .  I have had individual batteries go bad though. 

Lead acid batteries life span starts ticking as soon as the acid is in the cells no matter how little they have been used along the way.

[wbustraan]

The inverter charger and Classic won't interfere with each other. They will charge to their programmed setpoints. If the inverter charger has charged the battery all the way then the Classic will just go into float soon. If the batteries were only charged about 80% with inverter charger the Classic would finish off the charge. Neither one is going to charge and will go to float once their setpoints are reached.

Ok, that's a piece of information I was missing. So far, I've just been looking at "dumb" inverters and "dumb" chargers, that don't have setpoints. All of the battery chargers that you find in your typical retail store will just keep charging until the battery is 100%. If the battery dips below 100%, they start charging again. With a charger like that on all the time, the Classic would never kick in.

Does anyone have any recommendations of companies that carry lines of inverters that have that capability, that will play nice with a Classic, and aren't 5 times what the Classic costs? I mean, I can get my butt off the couch and monitor the system manually quite a few times for the cost of some of the "Cadillac" inverters.

If you get new batteries all the same date of manufacture you will be okay. If you get used batteries of different dates you may not find very good performance.  That being said I have a bunch of used AGM batteries on a 12v system but don't expect them to work to their rated capacity. But they work for the small loads I need .  I have had individual batteries go bad though. 

Lead acid batteries life span starts ticking as soon as the acid is in the cells no matter how little they have been used along the way.

I appreciate for the reminder. I'm aware that used/old batteries will certainly give reduced performance. I would want to replace them as soon as the budget allows. In the meantime, I figure that something is better than nothing.

[ClassicCrazy]

Darn  - I wrote  a long reply but it got lost. Basically I said a quality inverter charger that is sine wave and puts out a lot of amps will cost 3 or 4 times as much as the Classic. You could check out Samlex to see if they have a model , they are good quality and usually cost less than Outback, Magnum , or Schneider .

You could look for a used Trace non sinewave inverter charger - should cost a lot less and might do what you need if cost is an issue.