# C40 controller question



## JohnP (Sep 1, 2010)

I'm confused. I'm getting ready to put together a small PV system. 1-2 180 watt panels, 12vdc water heater element as diversion load, golf cart batteries etc.
Do I need two C40 controllers? One as a charge controller and one as a load divert controller.


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## 12vman (Feb 17, 2004)

No.. You can use the controller to divert the extra energy to a load and it will work normally. 

I wouldn't advise using it like that with a solar system. The diversion set up is for hydro or wind systems where there is constant charge 24/7 available to provide a constant load on the wind genny or the hydro charger when the battery is fully charged, using the diversion as the load instead of the battery.


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## JohnP (Sep 1, 2010)

I forgot that diverters were for wind/water power. I guess the controller just disconnects when batteries are charged and cuts back in when they need charging? (during sunlight)
How many 6vdc golf cart batteries per 180 watt panel would you recommend.

So basically this is all I need. (below is simplified, I'll be using xantrez diagram for "charge controller")


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## 12vman (Feb 17, 2004)

The C-40 will monitor the voltage of the battery and taper the charge when the battery reaches the user adjustable settings for bulk, float charge. (Bulk ~ 14.4/14.6 Float ~ 13.6/13.8)

180 watts of panel.. @ 12 volts..

180 divided by 17 = ~10.5 amps..

Fla., I'll figure 5 hrs. of charge time..

5 x 10.5 = ~52.5 aHr./Day..

Standard golf cart batteries have a capacity of around 200 aHr. reserve.. (@ 6 volt)

2 in series will give you 12 volts @ ~200 aHr. reserve..

Keep your daily usage @ ~ 50 aHr./day and you should be good. (25% discharge of battery)

Hope this helps..


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## Valleyguy (Jan 5, 2011)

JohnP,

You will want something like the C40 as the solar charge controller. The C40 in the "charge control" mode functions as 12vman explained to give proper battery charging.

When the batteries are full, indeed solar does not have to be diverted. However if you want to preheat water then I am not sure why you can not just run the C40 in the "diversion load" mode. I use a C40 as a diversion load controller to keep the wind energy in check. If I remember right the C40 diverts to the dump load (water heater) in bulk and float stages just like it would if it was in the charge control mode.

I think I would use a C40 between the panels and the battery and another hooked to the batteries and going to the dump load. You could set the charge control C40 to a slightly higher charging value than the dump load C40 so the full solar passes through to the battery and the diversion C40 handles the charging stages. Just thinking off the top of my head and don't have a manual handy to see if that works.

This would only be useful if you have a use for the excess energy from the panels, after the battery is full. Otherwise it is a lot of trouble and expense for nothing.

Rick
*Homepage*: www.power-talk.net
*Forum*: forum.power-talk.net/


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## JohnP (Sep 1, 2010)

Looking at the C40 wiring diagram, I see a shunt and a pvgfp. How important and what are they? Granted, I figured out that pvgfp is pv ground fault protection but doing a web search brought up nothing but the xantrex pvgfp at more than twice the cost of the controller.

I've read the definition of a shunt being a slight voltage reducer but the diagram shows it on the negative side which makes no sense to me. (neither does wanting to reduce pv power)

Regarding panel voltage/amps:

The C40 will take up to 125vdc input and I currently have two panels rated at the typical 18-21 vdc and 5 amps each. I've got them wired up in parallel to keep the voltage. Is there any benefit to wire in series to minimize wire size etc? I'm thinking down the road with more panels and not having to upsize wire. Would I lose charging amps by wiring in series or does the C40 convert the extra voltage into extra amps? (doubtful)


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## 12vman (Feb 17, 2004)

A C-40 uses Pulse Width Modulation (PWM) technology to charge a battery. Even though it will handle a higher voltage, it won't convert voltage into current like a MPPT type. (Multi Point Power Tracking Charge Controller)

http://www.wholesalesolar.com/Windy/MPPT-article.html

By using a MPPT controller, you could run your array voltage higher and use smaller gauge wire. (series your panels) With the C-40, you're better off to parallel your panels and gauge your wiring accordingly to distance and current load.

If you plan to use 12 volts as your system voltage, I wouldn't be concerned about pvgfp. The highest possible voltage would be ~21 volts open circuit with your panels connected in parallel. They mention pvgfp because the C-40 can be used to charge a 48 volt system. Open voltage on such an array could reach ~60+ volts open circuit! That could bite ya.. LOL

A shunt is a precision low ohm resistor that will drop a volt or two under a defined load. A meter is connected across this resistor to show how much drop there is across it. This shows how much current is passing in the circuit. IMO, a shunt could be inserted in the positive or negative connection.


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## adamtheha (Mar 14, 2007)

You don't have to use a C40 as a load diverter, a C35 would work just as well, and would cost less. If you have a larger array, and you want to use some of the excess summer sunlight to heat water, a C35 set to divert could be worth it, over a longer period of time. I have one sitting around that I haven't got a use for yet, it was only $95.


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