Load control circuits

Charge control circuit using relays to switch heaters based on battery voltage here

Heater control without batteries read on...

Here is a circuit for controlling heating loads on a wind turbine. It is intended for switching multiple small heating loads on and off. The circuit has various sections:

A tachometer circuit which takes input from the AC from the wind turbine and converts t to a DC level which represents the rpm. see left hand diagram below.
A number of Op-amp comparator circuits (can be one or two quad-op-amp chips) which compare this voltage (rpm indicator) to a reference and switch loads on at particular speeds. This circuit include feedback to increase its stability - it turns on at one rpm and then off at a lower one. This is achieved by a feedback resistor from the op-amp output to the positive input of the op-amp. Without this the load will switch on and off rapidly and cause some rumbling noises. The op-amp and an optocoupler circuit is shown below right.
Finally you need the power circuitry which actually handles the loads. It is possible to switch the loads onto individual phases of the wind turbine using a single triac driven by an op-amp comparator (as shown). But this results in unbalanced loading and hence some vibration in the wind turbine. A better solution is to use two triacs for each comparator (connect their two opto couplers in series) and put them in two of the feeds to a 3 phase bridge rectifier. Each load runs on the output from its 3-phase bridge (on DC). This is not shown in the diagram.

X-Sender: [email protected]
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Date: Mon, 2 Jul 2001 07:45:24 +0100
Subject: Re: [a-w-h] load control circuitry

At 5:30 pm -0600 1/7/01, Laurie Forbes wrote:

>. what voltage range does the input xformer for the f/v circuit need
>to supply?

Hardly anything. The chip just has to smell the frequency.

>. at what voltage do the clamping diodes need to cut in?

these are ordinary IN4001 diodes. They clamp the voltage at about
0.7 volts peak.

>. what wattage are the resistors?

say 1/4 watt.

>
>. on the triac driver circuit, does the 20K pot govern the frequency
>at which the triac is fully "on" or something else?

it sets the frequency at which it switches on. This happens fully at
once, not gradually. This circuit switches on fully at one frequency
and then off fully at a slightly lower one.

>. what is the initial cut-in frequency for this circuit?

that's what you set with the 20k pot.

>. part numbers for the op amp and switching transistor?

op amp can be a 741. any old transistor.

>. what purpose does the LED serve?

indicates that the load is on.

>. above you mention each triac control circuit switches two triacs
>for each load but only a single triac is shown on the circuit?

put the two opto-couplers' inputs in series with the led. They are
leds too, so you then have 3 leds in series altogether.

>. does the triac simply connect in series between the gen phase and the load?

yes it is like an AC switch.

>. what is approximate current consumption of each circuit (@ 12 V)?

20mA? something like that.

---------------

X-Sender: [email protected]
X-Apparently-To: [email protected]
To: [email protected]
Date: Tue, 3 Jul 2001 17:52:06 +0100
Subject: Re: [a-w-h] TACHOMETER CIRCUIT

>Hugh:
>
>Could you, please, give the complete value of the 2917 Tacho Chip

LM2917N from National Semiconductor (scottish nationalists? or not)

In the US you can get the 8 pin or 14 pin part from DigiKey

http://www.digikey.com/scripts/US/DKSUS.dll?Criteria?Ref=35036&Cat=18022921

> and who
>manufactures it.
>Same thing for the Opto Coupler 3061

MOC3061 triac driver optocoupler from Quality Technologies

there are many others which would do the job.

--
Hugh

http://www.ScoraigWind.co.uk

From: Laurie Forbes <[email protected]>
Date: Thu, 05 Jul 2001 20:11:47 -0600
Subject: [a-w-h] National Semi LM2917 Tacho chip

Had a look at National Semiconductor's web site and their 2917 tach chip
(used in Hugh's load control circuit). It appears this chip is a
combination tach *and* op/amp comparator + switching transistor which, with
addition of a couple of resistors to Hugh's tach circuit, can be used to
switch a relay etc. at a selectable input frequency thus apparently
eliminating the requirement for a separate op/amp switching circuit (or so
it appears to me). The chip also apparently has built-in hysteresis
although that does not appear to be adjustable.

I wonder what's missing here - this solution is considerably simpler than
two separate circuits but, may have disadvantages.

The URL for specs on this chip is:

http://www.national.com/ads-cgi/viewer.pl/ds/LM/LM2907.pdf

Laurie Forbes

=============================

(this would switch one load only - Hugh)

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