Solar Combiner Box -- used in a series?

PorkChopsMmm

I have built this solar panel combiner box from this site and it appears to be working for one 240 watt panel I have hooked up. I have 2 more identical 240 watt panels I would now like to wire into the combiner box. From what I have been reading I need to hook up my panels in a series.

With this sort of combiner box is there any downside or problems I will encounter if I use the bus bars of the box to wire string the panels together, mixing the positive and negative connections as appropriate?

Thanks in advance!

FreeWatts

Re: Solar Combiner Box -- used in a series?

combiners are used to parellel the strings of pannels that are wired in series.

is this a grid-tie?

PorkChopsMmm

Re: Solar Combiner Box -- used in a series?

FreeWatts wrote: »

combiners are used to parellel the strings of pannels that are wired in series.

is this a grid-tie?

No, it is off grid. Would it hurt to run a series through the combiner box? I already have it built and it is working for one panel.

arkieoscar

Re: Solar Combiner Box -- used in a series?

Unless you need to triple your voltage, you need to parallel the panels and this box looks like it will do it. Don't know what kind of breaker or rating you're using but if they are appropriate, it should be good.

PorkChopsMmm

Re: Solar Combiner Box -- used in a series?

arkieoscar wrote: »

Unless you need to triple your voltage, you need to parallel the panels and this box looks like it will do it. Don't know what kind of breaker or rating you're using but if they are appropriate, it should be good.

From the website I am using D Square 15 Amp breakers. I read that I needed a series since the increase in voltage will help charge my 8 battery (12 volt 55 amp hour each) paralleled battery array. Also the distance from my panels to my charge controller will be around 50 feet, if that helps.

mikeo

Re: Solar Combiner Box -- used in a series?

I read that I needed a series since the increase in voltage will help charge my 8 battery (12 volt 55 amp hour each) paralleled battery array

Yes you can series panels into the combiner but you may exceed the DC voltage that these breakers can handle. I would series no more than 2 panels which means you would have to purchase one more panel to get 2 strings of 2 panels at about 40 volts. You would then need an MPPT charge controller to charge the 12 volt battery bank. Also the breaker panel that you choose has no listing for DC use as far as I know. If you had bought the Square D series QO style box and breakers, they are rated to 40 volts DC and are available at many box store outlets.

PorkChopsMmm

Re: Solar Combiner Box -- used in a series?

mikeo wrote: »

Yes you can series panels into the combiner but you may exceed the DC voltage that these breakers can handle. I would series no more than 2 panels which means you would have to purchase one more panel to get 2 strings of 2 panels at about 40 volts. You would then need an MPPT charge controller to charge the 12 volt battery bank. Also the breaker panel that you choose has no listing for DC use as far as I know. If you had bought the Square D series QO style box and breakers, they are rated to 40 volts DC and are available at many box store outlets.

Sorry, I should have given more information. Below is my solar panel information from this thread I posted earlier. I have an Outback MX60 MPPT Charge Controller for managing the panel output.

Rated Power (Max) 240W
Tolerance +- 5%
Voltage at PMax (Vmp) 30.0V
Current at Pmax (Imp) 8.0 A
Open-Circuit Voltage (Voc) 36.0 V
Short-Circuit Current (Isc) 8.96 A
Nominal Operating Cell Temp (NOCT) 45 +- 2 degrees Celcius
Maximum System Voltage 600VDC
Maximum Series Fuse Rating 15A
Operating Temperature -40 to + 85 degrees Celcius
Fire Resistance Class C
Cell Technology Poly-Si

I may be mistaken, and usually am, but wouldn't having a 15 amp circuit breaker wired to each panel and then "series-ed" in the combiner box not trip the breakers since each panel is below the 15 Amp rating? I was figuring on having something like this configured in the combiner box...

Panel 1 - hooked up to 15 Amp breaker with positive to positive and negative to negative connections
Panel 2 - hooked up to 15 Amp breaker with positive to negative and negative to positive connections
Panel 3 - hooked up to 15 Amp breaker with positive to positive and negative to negative connections

I need to research the breaker panel I purchase. I bought a D Square outdoor 100 Amp box and 3 D Square 15 amp breakers, unsure of the model. They were the cheapest ones at Lowes.

mikeo

Re: Solar Combiner Box -- used in a series?

Open-Circuit Voltage (Voc) 36.0 V

Ok, you should run 3 strings of 1 (single) panels in this case with your combiner box with each string on a 15 amp breaker. You could get away with no combiner box and a 15 amp dc rated 150 volt fuse if you just wire all three panels in series to the mx60 controller. Your total current will be around 8 amps at 108 volts =864 watts and the output of the mx60 would be around 57 amps at 15 volts which is running near the MX60 maximum of 60 amps. OR you can buy a combiner that supports DC rated breakers to 125 volts or higher. If you use the panel and breakers that you already have use 3 15 amp breakers then a 70 amp dc rated breaker for the combined strings going to the charge controller. If you ever want to expand this system, I suggest that you look at using a 24 volt battery bank. If you don't have the QO series breaker box and breakers, I suggest that you take what you have back and either buy the QO series from the same store or take them back and by a commercial combiner box from our hosts website.

PorkChopsMmm

Re: Solar Combiner Box -- used in a series?

mikeo wrote: »

Ok, you should run 3 strings of 1 (single) panels in this case with your combiner box with each string on a 15 amp breaker. You could get away with no combiner box and a 15 amp dc rated 150 volt fuse if you just wire all three panels in series to the mx60 controller. Your total current will be around 8 amps at 108 volts =864 watts and the output of the mx60 would be around 57 amps at 15 volts which is running near the MX60 maximum of 60 amps. OR you can buy a combiner that supports DC rated breakers to 125 volts or higher. If you use the panel and breakers that you already have use 3 15 amp breakers then a 70 amp dc rated breaker for the combined strings going to the charge controller. If you ever want to expand this system, I suggest that you look at using a 24 volt battery bank. If you don't have the QO series breaker box and breakers, I suggest that you take what you have back and either buy the QO series from the same store or take them back and by a commercial combiner box from our hosts website.

Thanks for this information -- this is exactly what I was looking for. I will go home tonight to pull the model #'s off the D Square products.

If you were to put the panels in a series *without* the combiner box would you just twist the bare wire ends of the solar panels together to form the series and enclose in some sort of water tight box? This is what part of solar projects that is usually glossed over.

Thanks!

PorkChopsMmm

Re: Solar Combiner Box -- used in a series?

mikeo wrote: »

Ok, you should run 3 strings of 1 (single) panels in this case with your combiner box with each string on a 15 amp breaker. You could get away with no combiner box and a 15 amp dc rated 150 volt fuse if you just wire all three panels in series to the mx60 controller. Your total current will be around 8 amps at 108 volts =864 watts and the output of the mx60 would be around 57 amps at 15 volts which is running near the MX60 maximum of 60 amps. OR you can buy a combiner that supports DC rated breakers to 125 volts or higher. If you use the panel and breakers that you already have use 3 15 amp breakers then a 70 amp dc rated breaker for the combined strings going to the charge controller. If you ever want to expand this system, I suggest that you look at using a 24 volt battery bank. If you don't have the QO series breaker box and breakers, I suggest that you take what you have back and either buy the QO series from the same store or take them back and by a commercial combiner box from our hosts website.

I just checked and the outdoor breaker box I purchased is the QO series. The combiner box is up on my roof so it may take me a while to check the breakers. If it makes any difference the one panel I currently have hooked up to one breaker (of unknown series) is working fine.

mikeo

Re: Solar Combiner Box -- used in a series?

I just checked and the outdoor breaker box I purchased is the QO series

Then it is likely you have QO breakers since they have their own mechanical connection unlike any other brand of breakers that I know of. They are rated to 40 volts DC so be careful not to exceed their specifications.

PorkChopsMmm

Re: Solar Combiner Box -- used in a series?

mikeo wrote: »

Then it is likely you have QO breakers since they have their own mechanical connection unlike any other brand of breakers that I know of. They are rated to 40 volts DC so be careful not to exceed their specifications.

Thanks for the help, MikeO. Your advice is great. If I have a single panel, with specs listed below, tied to 1 of these QO breakers, is there any chance of me exceeding the 40 volts? I see 36 V in the specs -- does that give me enough room?

Rated Power (Max) 240W
Tolerance +- 5%
Voltage at PMax (Vmp) 30.0V
Current at Pmax (Imp) 8.0 A
Open-Circuit Voltage (Voc) 36.0 V
Short-Circuit Current (Isc) 8.96 A
Nominal Operating Cell Temp (NOCT) 45 +- 2 degrees Celcius
Maximum System Voltage 600VDC
Maximum Series Fuse Rating 15A
Operating Temperature -40 to + 85 degrees Celcius
Fire Resistance Class C
Cell Technology Poly-Si

mikeo

Re: Solar Combiner Box -- used in a series?

I just looked up the QO circuit breakers rating up and these circuit breakers are actually rated at 48 volts. I don't they will meet all the new code standards at that voltage. They would meet the 1.25 X rating at 36 volts but the AIR is only 5000 amps and more may be required to meet the new standards. The old standard would allow them if you fused the battery connection from the controller to the battery with a higher rated fuse or breaker with AIR of at least 10000 amps. That being said, if its your system and you do not require code inspectors, there are hundreds of 24 volt battery based off grid system that have used them safely for years.

PorkChopsMmm

Re: Solar Combiner Box -- used in a series?

mikeo wrote: »

I just looked up the QO circuit breakers rating up and these circuit breakers are actually rated at 48 volts. I don't they will meet all the new code standards at that voltage. They would meet the 1.25 X rating at 36 volts but the AIR is only 5000 amps and more may be required to meet the new standards. The old standard would allow them if you fused the battery connection from the controller to the battery with a higher rated fuse or breaker with AIR of at least 10000 amps. That being said, if its your system and you do not require code inspectors, there are hundreds of 24 volt battery based off grid system that have used them safely for years.

Thanks for the heads up. We will not be using code inspectors for this off-grid cabin. I really appreciate all of your help, truly.