Diversion Load

[megavolt]

Hi guys,

    I've got my 8' Hugh Piggott design mill up and running hooked up to my PLC control cabinet. I've got analog capability and am measuring voltage, stator current and DC current successfully. I'm charging a 190 AH 24V agm Battery bank. It's all presented to me on a 10" color touch screen in my living room.

    I noticed a bit of overcharging on these batteries the other day and decided to look into charge controllers. What I came up with is that I should buy a xantrex C60 (maybe a bit big but good for future expansion) because it would use PWM to charge my batteries and then float them while diverting excess power to my dump load. Not wanting to spend another 100 bucks on a DC water heating element, I looked for solutions. I came up with a Homepower article (Wrench Realities, Homepower#72, Aug '99) that said to use a C30 in the L mode or the load control mode and have the L+ and L- terminals turn on a solid state relay. This relay would then switch on AC from my inverter to fire my electric water heater with existing elements! Perfect.

    But, now after reading the user's manual for the C60, I see that if it is in the load control mode, it can't also charge the batteries.

    If I use the C60 in the diversion mode(to properly charge my batteries which is why I bought it) and the voltage of my mill goes too high, does it give a variable load (using PWM) to a DC element or does it simply turn the dump load on and off to control the voltage?

    If it is on and off then I can do that with a contactor controlled by the PLC but this may make the mill slow down suddenly causing the volts to go down turning the dump load back off again. Chattering action.

    I'm just not sure how the C60 could use PWM to charge the bank if wired after the battery bank and not in between the mill and the bank. Or does it only use PWM in the PV charge controller wiring scheme?

Longwinded, I know, but I'd rather give too much than not enough info.

Confused.

Thanks, Mike.

[Tom in NH]

Mike, The C-series controller connects the wind turbine directly to the batteries. When the batteries reach the bulk voltage setting the controller acts like a load controller. It connects the batteries to the dump load and holds the batteries at the bulk voltage setting for (I think) an hour. Then it bleeds more battery current to reduce the battery further down to the float voltage. Maybe others who have used the xantrex C controller in diversion mode longer than me can explain better, but I don't think PWM factors in when the controller is in this mode because alternator current does not go through it into the battery. The alternator is connected directly to the battery. The only pulse you would get would be the ripple left over from your rectifier. Your batteries can withstand a higher voltage generated by the alternator. In fact they will act like a big sponge and soak up the excess, holding the voltage to whatever the battery voltage is. --tom

[Flux]

Take this with a pinch of salt, I have never owned  C60, but as far as I know it uses the same pwm control for diversion as solar charge.

As you approach the set voltage I suspect it starts to deliver short pulses to the dump and as you feed more power in, the pulse width will lengthen so that the mean current balances the input to maintain constant volts.

When you reach the maximum input the thing will divert pure dc to the load resistor and that would be set to divert all input power at mill maximum out.

The resistor can be any value that will do this up to the limit of the controller.With battery at equalising volts the resistor should limit current to the maximum of 60A.

If you never produce more than 30A then the resistor can be chosen for say 40A.

Load control mode is a low voltage disconnect and will not use pwm and can't be used for charging.

If I have this screwed I an sure someone will correct me.

Flux

[s4w2099]

Yes this is true I have used teh C60 and its as you said. The gen goes straight into the battery. when it reaches the voltage that you set 14.4 for 12V and 28.8 for 24V banks it continues to charge at that constant voltage for two hours controlling the voltage diverting to an element and after that, even more power is diverted to the element to keep them floating.

It does PWM with solar panels though, because they dont need a load diversion it just disconnects the panels from the batteries for a period of time, checks the voltage and if needed it continues charging.