Please critique my solar plans

[twinboat]

Check out "vtewarehouse.com" for buss bars and posts.

They seem well made and less then Blue Sea.

[twinboat]

Check out "Copper Industries" for fuses

[Jill on Maya]

It looks as if this thread has almost come to an end with OP having obtained the information he asked for. I'd like to continue to seek a little more detail on the same topic. Have followed this thread with great interest as our current project is to install solar charging on our 48 ft mono. House battery bank is 675 Ah gels (3 x 225 12 volt).

Using information and following references on the forum we have purchased 2 x Sunpower E20 327 watt panels (knowing new model will be available soon but we could not wait). Plan is to separately connect each panel (via an isolating switch) to its own MPPT 30 amp, programmable controller (Powertech brand sold by Jaycar). The Sunpower panel specification gives a Voc (open circuit voltage) of 64.9V.

Is anyone prepared to assist with advice on these questions:

1. The Sunpower E20 panel does not state the nominal voltage rating, only gives the Voc of 64.9V. The Powertech controllers suit solar array of nominal 12V or 24V and max Voc of 65V. Should we be concerned that these controllers may not suit these panels?

2. OP says he is using a busbar to connect the output from the 2 controllers before connecting single connection to battery bank via a single breaker. Our plan is to take the output from each controller via a breaker and connect them after the breakers and take single connection to the battery. This seems to be the best way to create redundancy and maintainability without much extra cost. Any comments on pros and cons of these alternative set-ups?

[jbinbi]

Originally Posted by Jill on Maya

2. OP says he is using a busbar to connect the output from the 2 controllers before connecting single connection to battery bank via a single breaker. Our plan is to take the output from each controller via a breaker and connect them after the breakers and take single connection to the battery. This seems to be the best way to create redundancy and maintainability without much extra cost. Any comments on pros and cons of these alternative set-ups?

[OP]Would probably do the same. However, then you need a smaller gauge wire, and then have to potentially fuse that. I.e. you have 2 wires each with 25A to a breaker, then you need a wire to handle the 50A of the combined outputs. I think (somebody please correct me) that you should then fuse this single 50 smaller gauge wire. So now you have 2 breakers and a fuse. If you combine them prior to the breaker, you only need a single breaker. (i might be incorrect on this)

[ranchero76]

Originally Posted by monte

heres our L380 power budget

Is there place where I can look for this information about other cats? Thanks.

[Jill on Maya]

Originally Posted by jbinbi

[OP]Would probably do the same. However, then you need a smaller gauge wire, and then have to potentially fuse that. I.e. you have 2 wires each with 25A to a breaker, then you need a wire to handle the 50A of the combined outputs. I think (somebody please correct me) that you should then fuse this single 50 smaller gauge wire. So now you have 2 breakers and a fuse. If you combine them prior to the breaker, you only need a single breaker. (i might be incorrect on this)

Don't understand why you would use a smaller gauge wire after combining the outputs. If amps increase (from 25A before output joined to 50A after output joined), wire gauge should be increased. However in this situation our plan is to use the same gauge wire before and after input current is combined. Wire runs are very short so extra cost is insignificant. Plan is to use wire to suit up to 100A and fit a 100A breaker after each controller and before the two inputs join. After the join (via busbar or stud) use the same wire to suit up to 100A but carrying only about 50A. No need for additional breaker or fuse as the existing 2 breakers will provide protection and ability to isolate each controller. But if I have this wrong I hope someone can explain the error.

[mitiempo]

While the 2 breakers can be used to isolate the individual controllers they are not necessary for protection. One fuse or breaker after the bus bar close to the battery positive post is all that is necessary.

[socaldmax]

Originally Posted by mitiempo

While the 2 breakers can be used to isolate the individual controllers they are not necessary for protection. One fuse or breaker after the bus bar close to the battery positive post is all that is necessary.

I'm curious about that. Obviously, the fuse or breaker is supposed to be between the source of current (normally the battery) and the bulk of the cable or system, usually the load.

But in this case, the solar controllers and the battery are both sources of current, so even if one were to trip the breaker near the battery during the day, you could have current still flowing from the solar controllers to the short.

[mitiempo]

Originally Posted by socaldmax

I'm curious about that. Obviously, the fuse or breaker is supposed to be between the source of current (normally the battery) and the bulk of the cable or system, usually the load.

But in this case, the solar controllers and the battery are both sources of current, so even if one were to trip the breaker near the battery during the day, you could have current still flowing from the solar controllers to the short.

Correct, the panels are a source of current, but just like an alternator they are self limiting. The current from the panels will never be higher than their maximum capability. The battery, on the other hand, can produce thousands of amps if it is shorted.

As with an alternator one fuse near the battery.

Once the breaker tripe no current will flow as the circuit is interrupted.

[Jill on Maya]

Originally Posted by Jill on Maya

Plan is to use wire to suit up to 100A and fit a 100A breaker after each controller and before the two inputs join. After the join (via busbar or stud) use the same wire to suit up to 100A but carrying only about 50A. No need for additional breaker or fuse as the existing 2 breakers will provide protection and ability to isolate each controller.

If I interpret Mitiempo and Socaldmax correctly our plan above is good? Although one breaker/fuse close to battery would be enough for current protection, we want the two breakers to be able to isolate each controller. 100A waterproof breakers are not expensive ($30) even in Australia.

[mitiempo]

Originally Posted by Jill on Maya

If I interpret Mitiempo and Socaldmax correctly our plan above is good? Although one breaker/fuse close to battery would be enough for current protection, we want the two breakers to be able to isolate each controller. 100A waterproof breakers are not expensive ($30) even in Australia.

Yes, that works. The additional breakers are handy for isolation, just not necessary for protection.

[Ribbit]

I wouldn't worry about 'newer' panels, they are either monocrystalline or polycrystalline.

Right now, monocrystalline A1 cells are far and away the best for a reliable and long service life.

327 watts divided by 60 volts does not give you 25 amps feeding into a breaker, and the breaker to use should be a resettable fuse anyway (it trips when the amperage is reached) - so no need for a separate, additional fuse.

Remember watts = volts x amps, so amps = watts divided by volts.

The 60v wire is therefore carrying a max of 5.45 amps.

So put your charge controller very close to the battery bank (as 12v or 24v will be exiting it at the higher amperage) for very short low loss cable runs between them, and have your long runs to the charge controller with cheap thin cable, as 60v means very low losses (something like 1% over 30ft if I remember right - so not enough to worry about).

If you are getting a total of say 10 amps at 60v, as 10 x 60 = 600, that's the watts. 600 watts divided by 12 is 50 amps, and if it was a 24v battery bank, the amps would be 25 (it's why higher voltages with DC become very useful for saving money and providing long term reliability of cables, fittings, and components).

My home system is 48v for very good reasons (but that is providing 230v AC house current, not 12v DC).

[jbinbi]

Originally Posted by Jill on Maya

Don't understand why you would use a smaller gauge wire after combining the outputs. If amps increase (from 25A before output joined to 50A after output joined), wire gauge should be increased.

Smaller the gauge of wire, the higher the current carrying capacity , but really what is critical is the lower the voltage drop over the distance is. Which also means less heat generated by the resistance in the wire. (and thicker the wire is). A 28 guage wire is what you might compare to spaghetti. 2 gauge is as thick as your finger. Not exactly, but you get my idea.

Not trying to dis you, but If you don't know this, and Ohms Law, you might want to have an electrician or someone familiar with electrical stuff helping out.

[unclemack]

Originally Posted by jbinbi

Smaller the gauge of wire, the higher the current carrying capacity , but really what is critical is the lower the voltage drop over the distance is. Which also means less heat generated by the resistance in the wire. (and thicker the wire is). A 28 guage wire is what you might compare to spaghetti. 2 gauge is as thick as your finger. Not exactly, but you get my idea.

Not trying to dis you, but If you don't know this, and Ohms Law, you might want to have an electrician or someone familiar with electrical stuff helping out.

I hate AWG. Not the only cause of confusion here but "smaller gauge" should always mean "smaller size."

BSP sizes are nonsensical too.
Long past time all these ridiculously unwieldy national traditional standards were standardised globally.
I mean standardized, obviously.

As an old git I still think in Imperial but recognise the superiority of Metric SI.
Sorry for adding to the drift.

[twinboat]

LOWER the gauge, LOWER. Not smaller !!!