diversion load question

System · August 2009

I use a morningstar prostar 15m charge controller for my small PV system.. in the summer months the battery gets charge 100% very early during the day and the rest of the day i just have a blinking light telling me its full.. whats the cheapest diversion load I can use for this excessive energy? meaning spending the less amount of money to make use of the excess power.. thanks

niel · August 2009

Re: diversion load question

most will use something like a resistive heating element like for heating water. if you run out of water the element can burn out though. look around as their are some popular pwm controllers that have this ability. c40 comes to mind right off the top of my head.

Solar Guppy · August 2009

Re: diversion load question

Add another battery to have the energy available later

mike95490 · August 2009

Re: diversion load question

With solar, not haveing a "diversion load" causes no problem. At least you don't have a dead battery

System2 · August 2009

Re: diversion load question

what I don't understand is that if you use the C40 as a diversion load controller does it still maintain its charge controller features? since I've been reading these controllers can only do 1 function at a time.. i still need it to protect my battery (i.e charge or divert the load).. is this a given that it does this when in diversion mode?

also.. if i use hot water elements as my diversion load as suggested how will a 12vdc source heat a conventional 240VAC hot water tank?? or is there special tanks for this purpose than run in DC?

Solar Guppy · August 2009

Re: diversion load question

The C40 can only do one or the other function. PV does not require a diversion controller, as the C40 will just stop charging when the battery is full. Its wind generators that need diversion load to stop over speed conditions

tallgirl · August 2009

Re: diversion load question

solarguy wrote: »

what I don't understand is that if you use the C40 as a diversion load controller does it still maintain its charge controller features? since I've been reading these controllers can only do 1 function at a time.. i still need it to protect my battery (i.e charge or divert the load).. is this a given that it does this when in diversion mode?

also.. if i use hot water elements as my diversion load as suggested how will a 12vdc source heat a conventional 240VAC hot water tank?? or is there special tanks for this purpose than run in DC?

Generally speaking, at the point when "diversion" comes into play, there isn't a lot of "charging" left to do.

Likewise, for PWM controllers they aren't all that incompatible. If the battery voltage is below a cut-off, connect the source to the batteries. If the battery is above a cut-off, connect the source to the diversion load.

System2 · August 2009

Re: diversion load question

so if I understand well, if its in diversion mode the battery will not overcharge when its full right?

tallgirl · August 2009

Re: diversion load question

solarguy wrote: »

so if I understand well, if its in diversion mode the battery will not overcharge when its full right?

Correct. Because the purpose of the diversion load is to get rid of the power that would do that in the first place.

In reality they only "Do" one thing at a time. It just happens to be that the "one thing" has two different effects.

Solar Guppy · August 2009

Re: diversion load question

Diversion is not a state for charging battery's, its a feature to apply an unregulated load. So for example you have a pwm controller configured for diversion, it will turn on at a set voltage point, unfortunately, if the load is large, not only will it divert the charging source , with PV it can drain the battery.

If all you have is PV, you do not want to have a diversion controlled load

dwh · August 2009

Re: diversion load question

solarguy wrote: »

also.. if i use hot water elements as my diversion load as suggested how will a 12vdc source heat a conventional 240VAC hot water tank?? or is there special tanks for this purpose than run in DC?

Not a special tank, a special heating element that runs at 12v (or 24 or whatever).

http://www.survivalunlimited.com/diversionloads.htm

If it were me and I had to solve this problem...

I might buy a small tank, stick a 12v element (or two) in it, and plumb it with a small circulation pump to my main tank. Then, when the "diversion" is happening, both the heating element and the pump are running. If nothing else, it would serve as a "pre-heater" so the heater in the main tank (electric or gas) wouldn't have to run as much.

Now how long it would take to amortize the investment...I dunno, I'm too lazy to do the math so I leave that as an exercise for the reader.

Windsun · August 2009

Re: diversion load question

We are not fans of diversion loads for one main reason, and that is because if they fail, it can be a disaster.

A diversion controller can fail in the "shorted" mode, in which case it will totally drain the batteries down to zero volts, most likely ruining the batteries. You might thing a fuse or breaker would solve that problem, but then you run into the next type of failure:

It can also fail in the "open" mode, in which case you may end up having no control at all over what the panels or other source is feeding to the batteries. If your panels are putting out 18 volts to your 12 volt battery, it won't take a long time to do horrible things to them.

Kamala · August 2009

Re: diversion load question

From what I have learned in my ~6 mos on this forum, diversion is unnecessary for PV/BB with a proper SCC. You simply can't "harvest" the SE... it's lost. It won't affect your system because you haven't harvested it. An earlier post mentioned that diversion was only a factor in wind driven systems. This makes sense to me. I don't recall, and haven't tried to find out if wind was part of the OP, but I don't think so.

Craig

halfcrazy · August 2009

Re: diversion load question

If all you have is PV and you are worried about losing extra power you can use a Charge Controller like the MF60 and a solid state relay to power a heating element or something. I forget what outback calls it opportunity mode or something?

That said I agree with Wind and Sun if there is no wind turbine don't bother it is just another failure point. just run some loads manually if you are there.

tallgirl · August 2009

Re: diversion load question

halfcrazy wrote: »

If all you have is PV and you are worried about losing extra power you can use a Charge Controller like the MF60 and a solid state relay to power a heating element or something. I forget what outback calls it opportunity mode or something?

That said I agree with Wind and Sun if there is no wind turbine don't bother it is just another failure point. just run some loads manually if you are there.

There's also using Outback's "Load shed" feature.

ADV/FX/AUX----------
aux output Load Shed
function
DOWN  INC  DEC

then

ADV/FX/AUX----------
loadshed    42.0 vdc
off setpoint
DOWN  INC  DEC

When the battery voltage falls below a certain value (pick a high one ...) the AUX relay turns on. Use that to control an AC load that's consuming spare solar power.

(And for those of you who are new to seeing me post, if you want to see what made those screens, go here.

mshen11 · August 2009

Re: diversion load question

[ AUX relay turns on. Use that to control an AC load that's consuming spare solar power.]

forgive me for being dumb (i cant view the link from work)... can you elaborate on that? the FM60 has an AC port (inverter?) to plug in AC devices???

mike95490 · August 2009

Re: diversion load question

Use the excess power to run a fan for your windmill

BB. · August 2009

Re: diversion load question

I believe the issue is the Aux port (on most controllers) only supports a very small output signal (see manual for your unit).

You would have to drive a DC Relay (to control DC loads), Inverter remote (using the remote control available on some inverters), or AC solid state relay (on the inverter AC output) to use the excess power.

-Bill

dwh · August 2009

Re: diversion load question

tallgirl wrote: »

When the battery voltage falls below a certain value (pick a high one ...) the AUX relay turns on. Use that to control an AC load that's consuming spare solar power.

Why does that sound backwards to me? When the voltage *falls* to a certain point, shouldn't that turn the AUX load *off*?

Conversely, when the voltage *rises* to a certain point, should that not turn the AUX load *on*?

Cariboocoot · August 2009

Re: diversion load question

I don't know about other controllers, but the MX60's aux function can be programmed to activate under a number of different circumstances. For load diversion, you'd set it to turn on when the batteries reach "float". It can fire a 12V, 200mA relay that can activate an additional AC load, say. If you watch your panel output carefully, you'd know that under float mode you only use "X" Amps of an available "Y" potential. Setting a diversion load that is just under the X-Y differential makes good use of the solar power you would otherwise not be harvesting (it is wrong to say "wasting"). This could be when you turn on the water pump and refill your storage tank, for example. That's what I do, but I do it manually because I'm always a little leery of too much automation.

tallgirl · August 2009

Re: diversion load question

dwh wrote: »

Why does that sound backwards to me? When the voltage *falls* to a certain point, shouldn't that turn the AUX load *off*?

Conversely, when the voltage *rises* to a certain point, should that not turn the AUX load *on*?

I hate to admit this, but experimentation is the only way for me to make sense of the documentation. The value is "Load Shed Off", but the indication is that the AUX relay is turned ON when the condition is reached. Maybe.

diversion load question

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