Newbie with some questions

[joehump]

I just built a new solar panel. 36 cells, rated at .5 volt and 8 amp. From what I read these are the newest and best. I can get anywhere from 17.5 to 20 volts during the day.
I have a Xantrex c60. I have it set for charge controller. The bulk charge is set to 14.8 volts and the float charge is set for 13.5 volts.
Is this correct?

I have 2 T105 Trojan batteries in series. Rated at 225 amp hours.

I have a Cobra 1500 watt inverter.

The panel is located about 75 feet from the C60. I am using 14 gauge stranded. Is this ok? I measured the voltage at the panel and at the C60 and there was virtually no difference.

Do I need a 10 amp Diode? I believe the C60 has one built in.

I ran the batteries down to 11.3 volts the first night just to give everything a good test, but the highest I have been able to charge the batteries back to is only 12.2 volts. I had 2 full days of sun.

I think that I have everything hooked up correctly. I am using 4 gauge from Xantrex C60 to the batteries and 4 gauge from the batteries to the Cobra 1500 inverter.

Thanks in advance for any pointers. So far this has been a very informing and fun project. I plan on building 2 more panels.

[icarus]

Quick comment,

I would guess that you would be LUCKY to ~ 9 amps out of your panel if I do the calcs right. A C 60 is a pretty big controller for only 9 amps. I would guess there is a fair bit of inefficiency there. Second, # 14 is pretty small to run 75'. There is a "sticky" with a voltage drop calculator in this forum. I suggest that you look at it. Third, running your batteries down to 11.3 volts is a really bad idea! Compound this by not FULLY charging them within a matter of a couple of days will put them on the road to scrap metal. I suggest you look at the following:http://www.batteryfaq.org/ http://www.windsun.com/Batteries/Bat...of%20Batteries

The important measurement is not how many VOLTS you get our of a panel, but how many AMPS you get at WHAT VOLTAGE (watts) 17.5 volts @1 amp= 17.5 watts, same 17.5 volts @ 10 amps = 175 watts. It is also important to remember that unless you use a MPPT controller, you will never get the stated WATTAGE out of any given panel unless your battery voltage were to rise to the Vmp of the panel, which in this case would cook the battery. So lets say you were getting 9 amps @ 17 volts, you would get 153 watts. Put that same 9 amps at 12.6 volts and you would only be getting ~113 watts.

A rough rule of thumb is that flooded batteries need to be charged at a current between ~5-15% of ah capacity (11-23 amps) just to maintain charge.

At this point I wouldn't worry about float or even absorb voltages as you are unlikely to ever get there.

Finally, if you expect to run your inverter anywhere near 1500 watts you will not have nearly enough battery, except for very short term (minutes) loads.

Welcome to the forum, good luck, and read all you can here and elsewhere. There are some pretty sharp folks here who have forgotten more than most of us will ever know. Using this resource allows us not to have to re-invent the wheel each time,

Tony

[joehump]

Thanks for the info on this. It sounds to me like I need more panels for more watts to power the batteries. I was actually planning on getting 2 more T-105 trojans and building 2 more panels.

What kind of amperage should I be putting into the charge controller in order to get those batteries back up to where they should be?

I dont want to start off by ruining 2 perfectly good batteries.

I will replace the cable tommorrow with the correct gauge wire from the panel to the charge controller.

Thanks again in advance.

[mikeo]

What kind of amperage should I be putting into the charge controller in order to get those batteries back up to where they should be?

I would shoot for around 10% of your battery capacity, in this case around 22 amps. A 20 amp battery charger would do the trick very well, you could get by with a 10 amp battery charger if you have one available to get the batteries charged back up. A 8 amp panel is just not enough.

[joehump]

Thanks MikeO.

Im living and learning. My cells should be delivered by aboaut Tuesday so hopefully by about Friday I can have them put together.

I fortunatley still have my day job.

Thanks again for the info. Its all starting to make more sense.

[joehump]

One other thing that I have noticed and dont really understand.

I measured the voltage on the batteries before the sun went down and measured 12.2 volts. I measured again a couple of hours later and I measured 12.0 volts.

Is this normal? I have everything turned off. Just wondering.

I have the cables from the panel going to the C60 and then from the C60 to the Batteries. I am measuring from the C60 and from the Batteries. Both show 12.0 now.

Is this correct?

Thanks

[mikeo]

The panel is located about 75 feet from the C60. I am using 14 gauge stranded. Is this ok? I measured the voltage at the panel and at the C60 and there was virtually no difference.

You need at least #6 wire for this run from the panels to the controller to maintain a less then 3% drop at 8 amps.

Do I need a 10 amp Diode? I believe the C60 has one built in.

You are correct, no diode is needed.

I ran the batteries down to 11.3 volts the first night just to give everything a good test, but the highest I have been able to charge the batteries back to is only 12.2 volts. I had 2 full days of sun.

You will need 3 of these panels to properly charge and maintain this battery bank, any less and you will kill the batteries prematurely.

I think that I have everything hooked up correctly. I am using 4 gauge from Xantrex C60 to the batteries and 4 gauge from the batteries to the Cobra 1500 inverter.

at full load you will be drawing 125 amps. You will need at least 2 AWG to maintain less then 5% drop in voltage, 1 or 1-0 would be better.