Wiring inverter to charge controller/battery?

[PNjunction]

Couple of things to keep this fun:

Do you have the manual for the charge controller? I checked the description, and it shows a 13.7 volt cutoff for full charge. If that controller only charges up to a float voltage of 13.7 it is going to take a long time to charge. Typically, a cc should have a spec of anywhere from 14.3 - 14.6v or so for the cyclic use you are putting it to. And, it shows a low voltage cutoff of 10.5 volts - might as well kiss that battery goodbye if you rely on that.

I'd suggest a reliable little pwm controller like a Morningstar Sunguard 4.5a unit. That ebay charge controller is freaking me out.

You can check how well your charge is by letting the battery rest for at least 4 hours with no charge or discharge, and taking a voltage reading. Shirt-pocket multimeters aren't accurate enough.

AGM's:
12.8V + = 100% charge (typically 13v seen for really fresh well maintained agm's)
12.6 = 75% charged (recommended no lower for longest cycle life)
12.2 = 50% charged (lowest I'd go)
11.8 = 25% charged (don't go here)

Other things to look into is what gauge and length of a run of wiring do you have going from the roof to the charge controller/battery combo, and solar insolation hours for your area. I feel that your battery is just not getting enough of a charge.

[PNjunction]

.. For a 12 volt AGM battery here is a general rule of thumb. For each 10 AH of battery can run 30 watts of inverter.
For a 12 volt flooded battery for each 10 AH of battery can run 15 watts inverter..

You just took the fun out of my complicated spreadsheet. Seriously, thanks for breaking that down between AGM and FLA so simply. Saved me some bucks since I was going to buy another one that was too large to be efficient, despite not being able to support a huge load in the first place.

[sultan316]

Couple of things to keep this fun:

Do you have the manual for the charge controller? I checked the description, and it shows a 13.7 volt cutoff for full charge. If that controller only charges up to a float voltage of 13.7 it is going to take a long time to charge. Typically, a cc should have a spec of anywhere from 14.3 - 14.6v or so for the cyclic use you are putting it to. And, it shows a low voltage cutoff of 10.5 volts - might as well kiss that battery goodbye if you rely on that.

I'd suggest a reliable little pwm controller like a Morningstar Sunguard 4.5a unit. That ebay charge controller is freaking me out.

You can check how well your charge is by letting the battery rest for at least 4 hours with no charge or discharge, and taking a voltage reading. Shirt-pocket multimeters aren't accurate enough.

AGM's:
12.8V + = 100% charge (typically 13v seen for really fresh well maintained agm's)
12.6 = 75% charged (recommended no lower for longest cycle life)
12.2 = 50% charged (lowest I'd go)
11.8 = 25% charged (don't go here)

Other things to look into is what gauge and length of a run of wiring do you have going from the roof to the charge controller/battery combo, and solar insolation hours for your area. I feel that your battery is just not getting enough of a charge.

Ok this is really pissing me off. I just went back on my roof to fully seal my panel because it had opened up a little because of the heat. I hosed it down because it was really hot and the plexiglass warped a bit. I plug in my laptop (at 2pm with great clear weather) and it charges and works fine. Less than a minute later, my inverter starts beeping at me. While the light is still green and charging, it is beeping at me. I'm assuming it's because not enough voltage is available. While using my multimeter I found about 14V at both the battery terminals as well as at the point on the CC where the panel hooks up to. I'm pretty sure thats not enough voltage coming from the panel, but is that really my panel's fault, or is it the CC's fault? I have 39 cells up there and while they're grade B, it was guaranteed less than I believe 5% gone.

Ahh I just want this thing to work already so I can let it be and stop spending money on it.

[billvon]

While the light is still green and charging, it is beeping at me. I'm assuming it's because not enough voltage is available. While using my multimeter I found about 14V at both the battery terminals as well as at the point on the CC where the panel hooks up to.

That's not unusual if you have an MPPT controller and a partially charged battery. The battery is pulling the panel voltage down to its own voltage (14V.)

If your inverter is beeping at you AND the voltage is 14V at the inverter terminals AND there are no suspicious transient loads to load it down momentarily - there's something wrong with the inverter. Every 12V inverter out there sees 14V as a good battery.

I'm pretty sure thats not enough voltage coming from the panel, but is that really my panel's fault, or is it the CC's fault?

Disconnect the charge controller. If the panel voltage shoots up to 20ish volts then the panel is giving you enough voltage. It may not be giving you enough current at 14V to charge your battery but that's a different problem. To really check that out you'd need an active load, or at least a very large variable resistor to do a V/I sweep of the panel.

I have 39 cells up there and while they're grade B, it was guaranteed less than I believe 5% gone.

Right. But you may also have bad solder connections, you may have damaged them during assembly etc.

Ahh I just want this thing to work already so I can let it be and stop spending money on it.

That's the nature of homebuilt systems - you learn a lot about solar but they never work quite right.

[Sunking]

Less than a minute later, my inverter starts beeping at me. While the light is still green and charging, it is beeping at me. I'm assuming it's because not enough voltage is available. While using my multimeter I found about 14V at both the battery terminals as well as at the point on the CC where the panel hooks up to.

None of that matters. What is the voltage at the inverter input terminals. Sounds like you have a wiring problem as the inverter should work down to about 10.5 to 11 volts

Ahh I just want this thing to work already so I can let it be and stop spending money on it.

That is why we never recommend making your own panels. Today it is less expensive to buy them and they actually work for a long time. By this time next year or sooner your panel will be in the dump.

[sultan316]

Ok so you guys brought up good points. I'll disconnect the CC tomorrow at around the same time and test the voltage to see if it shoots up.

Now as for my inverter. I bought it brand new, so in theory it should be perfect. I might not have it hooked up right. It's one that connects to a car lighter, so I bought an adapter to connect to battery terminals. I only connected it to my battery using alligator clips (+ to +, - to -). I have nothing from it to the CC. Didnt think that was necessary.


As for making my own panel instead of buying it. I have a strong interest in solar energy/technology, so I did this as a simple project for pure learning purposes. I'm not trying to save money on my energy bill or anything really (yet). Only a single panel, but I will definitely buy my next ones haha

[billvon]

Now as for my inverter. I bought it brand new, so in theory it should be perfect. I might not have it hooked up right. It's one that connects to a car lighter, so I bought an adapter to connect to battery terminals. I only connected it to my battery using alligator clips (+ to +, - to -).

Alligator clips? I see your problem. Alligator clips are good for temporarily hooking up low power DC circuits and that's it. They will cause your inverter to trip out very quickly due to their high (and often unrepeatable) resistance. You need real (i.e. reliable low resistance) connections there.

[sultan316]

Alligator clips? I see your problem. Alligator clips are good for temporarily hooking up low power DC circuits and that's it. They will cause your inverter to trip out very quickly due to their high (and often unrepeatable) resistance. You need real (i.e. reliable low resistance) connections there.

Seriously? How do I permanently/reliably hook them up then? I thought the best way was through alligator clips...

[billvon]

Seriously? How do I permanently/reliably hook them up then? I thought the best way was through alligator clips...

Yes, seriously. Using alligator clips for inverters is like using duct tape to fix your car. Might work in some cases, but it's not going to last - and you pretty much expect it to fail after a while. Use correctly rated wire with good lugs on the end (preferably crimped with a real crimp tool, not a pair of pliers). And of course use the right circuit protection.

[sultan316]

Yes, seriously. Using alligator clips for inverters is like using duct tape to fix your car. Might work in some cases, but it's not going to last - and you pretty much expect it to fail after a while. Use correctly rated wire with good lugs on the end (preferably crimped with a real crimp tool, not a pair of pliers). And of course use the right circuit protection.

Ok, but I would think they should work at least for a little. I've only just tried them. How can I even convert it to a wired connection onto the lug nuts? Like I said its meant for a car lighter slot, and I used an adapter to convert to alligator clips.

Also, I tested my panel today by removing from the CC. It shot up to about 18V which is great. This tells me that the panel is working fine. Problem lies on the floor, but what....

[Sunking]

Billvon I suggest you be careful with recommendations. You are talking to someone who has no understanding of what they are doing and you are now going on hook for being responsible and liable. That is why I DO NOT give nuts and bolts advice. A lawyer can track you down very easily in 5 minutes.

[sultan316]

Billvon I suggest you be careful with recommendations. You are talking to someone who has no understanding of what they are doing and you are now going on hook for being responsible and liable. That is why I DO NOT give nuts and bolts advice. A lawyer can track you down very easily in 5 minutes.

ok then besides advice on nuts and bolts. Honestly, I feel like it's going to make no difference. I do have some wiring and electronic background from classes, and I think the problem isn't with alligator clips (even if it may not seem like a permanent solution).

Can someone just let me know where the problem is most likely lying (i.e. CC, inverter, wiring)? I've eliminated the panel and I've given the specs and wiring of everything. I dont know what else I can provide.

[Sunking]

ok then besides advice on nuts and bolts. Honestly, I feel like it's going to make no difference. I do have some wiring and electronic background from classes, and I think the problem isn't with alligator clips (even if it may not seem like a permanent solution).

OK I will give you a hint. Your problem is voltage drop from current flowing through resistance. Meaning your connections are poor, and/or you wire is too small and too long. That is why I asked early on: What is the voltage at the input of the inverter? You have not answered that yet, and that is you rproblem. You have already determined the voltage is fine at the source, but your inverter goes into under voltage alarm when loaded up. Figure it out.

[sultan316]

OK I will give you a hint. Your problem is voltage drop from current flowing through resistance. Meaning your connections are poor, and/or you wire is too small and too long. That is why I asked early on: What is the voltage at the input of the inverter? You have not answered that yet, and that is you rproblem. You have already determined the voltage is fine at the source, but your inverter goes into under voltage alarm when loaded up. Figure it out.

ok but how do I measure the voltage at the input of the inverter? Isn't the input of the inverter at the battery terminals? If so, that typically fluctuates between 11-14V like I said before.

[epsgunner]

Usually taking a DC meter will tell you the VOLTS at the end of the wire from the battery bank to the inverter..

Put leads on the ends of the wire where they hook onto the inverter itself..