Wind gust spike voltage and shut off inverter

[RickR]

I've got my 12Ft 24 volt windgen up and running charging 6 car batteries using a Xantrex C40 diverting extra power to heating elements. I set the bulk voltage to 28 and float to 27vdc and it seems to work fine dumping extra voltage when it needs to. During winter I've been just letting it dump everything it can into heat thru the heating elements.  Lately its' been warming up so I've been playing around with an inverter to use some juice. I've noticed with wind gusts the voltage spikes to 30 volts befor the c40 can divert and shuts it off my inverter.

Is there somthing I can do to keep my inverter from seeing those spikes??

[Tom in NH]

Are you using a temperature sensor and if so, is it cold where it's located? The temperature compensation scheme will raise the voltage when the batteries are cold, and sometimes it will raise it higher than an inverter's overvoltage cut-off. --Tom

[richhagen]

I have been using a C40 to divert a 48V solar setup.  I have noticed that the C40 does not start to divert based soley on the voltage.  If the voltage shoots up quickly, the voltage will get higher before it starts to divert than if the voltage rises slowly.  I appears to me it uses an alogrithm to decide when to dump that takes into acount the voltage and the time as factors to decide when to throw the switch.  You can adjust the set points a bit, but I'm assuming you've already looked at that.  If your generation is larger relative to your battery bank, this will be more of a problem.  

One way around this might be to build a soley voltage dependant switch based on an op-amp comparator circuit with a zener diode on one leg and a voltage divider on the other with a potentiometer on one of its legs to adjust it, and a bit of hysterisis by feeding back a bit of power from the output to the voltage divider leg through a resistor to prevent it dropping the voltage below the threshold voltage on the input as soon as it is turned on. That prevents it from continuously switching at the threshhold voltage.

Kind of like the 12V battery monitor example on this page, but with the transistor circuit to throw a relay on the output like in the auto fan examble, but with a more robust transistor, and a relay capable of switching the amps for a dump load:

http://www.uoguelph.ca/~antoon/gadgets/741/741.html

I'm not a circuit guru of the board like some who frequent here, but I have built a few simple op-amp circuits, and in my experience they work reliably and predictably well.  Rich

[RickR]

No, I never hooked up the temp sensor for the c40.  The batteries, controller, and inverter are all in doors.

[Hank]

Hi Tom,

A bit off post but your Temp sensor worked out real fine. Today I had an opportunity to get out to the land after the freeze and installed it. Initially I thought it was not working correctly as it was calling for more volts then before (it was 20 deg.) but when I warmed it in my hand you could see the voltage requirement drop (state of charge). I could see this by the amount of blinks I got on the LED on the C40.

RickR,

I run a 12 volt system connected to Solar panels, wind pmg and occasionally a diesel powered alternator. I have never had my inverter trip out due to over voltage. The C40 reacts almost instantly to keep it below 15 volts.

As another poster speculated you may have to small a batttery pack for your system which could result in a rapid voltage spike when your pma puts out high current in a wind spike. I'm running with a 1000 amp-hour battery package. Judging from what you wrote it appears you only have about a 300 amp-hour system although at 24 volts.

What's the output of your wind mill or it's rating?

[RickR]

I've looked thru the examples you sugested and could handle building it but I don't totally understand what this circuit would do. Some of this is a little over my head.  Is this a voltage regulator that would constantly let no more then the set voltage thru or  would this shut off all power when above the set point??  

[RickR]

I've wondered about the batteries, I've got a mix, 2 smaller car batteries , 2 deep cycle marine, and two 6 volt out of tractors I don't use in the winter. There all hooked up in kind of a series, paralell mess.  Eventually I'd like to get an old forklift battery but for now I had these just sitting around so it was cheap to get started.  I built this using Hughs 12ft dia plans and have seen 1000watts max. I have seen the spikes in lower winds where outputs were 200 to 300 watts.

[Hank]

Rick,

Gut says this is where your problem is.

A big no no... is mixing batteries, same battery types of different ages is not to good. Mixing batteries of different sizes, types and voltages is even worse. They all have different amp-hr ratings and charging requirements and I can see where you could get a high voltage spike.

Hope you're not using all these batteries together at one time in a series-parallel system as you can't combine them all together and come up with a 24 volt system.

Chinese tractors?

[Hank]

Just as an after thought,

You said you are using the C40 in the diversion load mode.

Did you make sure the internal switches are set correctly? Is your load (heating elements) capable of handling the load?

[Hank]

Opps!  I guess you could wire all these batteries into a 24 volt system but still not a good idea.

[Flux]

I have never used a C40 but I believe it is common knowledge that it is slow responding, I have heard of this over voltage spike shutting down inverters before.

The problem is no doubt made worse by your indifferent batteries.

Richhagen' solution would be fine, but it does defeat the idea of using a C40 if you have to build something to override it during gusts.

Maybe your inverter has a rather low "high volt" setting.

Try setting the C40 voltage a little lower and perhaps raise it for a short time when you know the batteries have been well down and want equalising.

Flux

[richhagen]

It just throws a relay (switch) when the voltage gets above a certain point that you set.  Flux is, of course, right, it would be redundant to the C-40's purposes as a dump load, but a little redundancy isn't necessarily a bad thing.  

As I mentioned above, it strikes me that this problem will likely only occur if your input current is large relative to the size of your battery bank.  You could also likely fix the problem by having a larger battery bank, which would slow the voltage rise, everything else being equal.  :-)  Rich

[RickR]

Thanks for the input, this will give me some things to try, I appreciate the help.