Author Topic: Moteino, 4 AAA 1.5V batteries and two relays  (Read 2777 times)

chspter

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Re: Moteino, 4 AAA 1.5V batteries and two relays
« Reply #15 on: March 02, 2017, 01:03:53 PM »
Some days ago I soldered the 'slave' board. Now I added all proposed modifications which took a bit of unsoldering. Never really done this, so I do not really know if the tracks on the board could use less solder, but it seems to work all good.

TomWS

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Re: Moteino, 4 AAA 1.5V batteries and two relays
« Reply #16 on: March 02, 2017, 04:08:39 PM »
I don't know if it's the perspective or not, but your antenna wire looks a tad short.

Otherwise, good job!

Tom

chspter

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Re: Moteino, 4 AAA 1.5V batteries and two relays
« Reply #17 on: March 13, 2017, 04:40:31 PM »
I don't know if it's the perspective or not, but your antenna wire looks a tad short.

Otherwise, good job!

Tom

From the board to top it currently measures around 75mm. It keeps being shorter everytime the antenna breaks at the base from too much twiddling around. Once the boards are stable on a box I plan to add an SMA and an antenna, which I think is going to be an adventure on itself...

Yes, this is exactly what I suggested.In this case, you could use another NPN transistor and use it as a voltage follower.  As a 'follower', the collector is tied to Vin.  The base is tied to 3.3V, the emitter to the power supply of the relays.  I did not check on how much current the relays draw, but if it's a lot (which it may be, being low voltage relays), then you'll need a Power NPN transistor and possibly a heat sink if you do plan to operate from 12V.  You can calculate power as W = Ir * Vd, where Ir is total current of the two relays (in Amps),  Vd is the voltage drop across the power transistor and is equal to Vin - (3.3-0.7)   0.7 is the voltage drop from the Base to Emitter.  The advantage of this circuit is very low quiescent current when the relays are off.

Tried the voltage follower (although, I do not understand why it works, which is bad) and it worked as described. Got the reference voltage minus 0.7. But boy did the NPN heat up when power was going through (that was at 9V). When I went to the shop to ask around for a Power NPN and a heat sink, they recommended instead a voltage regulator fixed at 3.3V, together with a heat sink. It wasn't really expensive, so I went with that too (LM 1117T-3.3 http://www.ti.com/lit/ds/symlink/lm1117.pdf). Tested it and it works, 800mA is more than enough for the two relays. On the PDF there are some reference circuits using two condensers (a 10uF and a 100uF) on the input and output, connected to the ground. I guess the condensers keep the input and output stabilized.

At this point I have many questions. Is a voltage regulator just a voltage follower with a diode somewhere to tune the reference voltage and some heat protection? I have seen some diagrams on voltage followers on the internet and they all include a zener and some resistences to tune the reference voltage. Maybe a regulator is just a voltage follower with all these things packaged. Otherwise, is there any pros or cons on using one or the other?

The other question is: does the voltage follower (an NPN, maybe with a heat sink, with base connected to Vref, collector to the Vin and emitter as Vout, being Vout = Vref - Vd) have any other components involved (resistors maybe?). I want to know more about this circuit, it looks really useful. All things I found on the internet about this have zeners and resistors to tune Vref.

Attached the current revision of the 'master' board.
« Last Edit: March 13, 2017, 05:04:28 PM by chspter »

TomWS

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Re: Moteino, 4 AAA 1.5V batteries and two relays
« Reply #18 on: March 13, 2017, 06:01:46 PM »
From the board to top it currently measures around 75mm. It keeps being shorter everytime the antenna breaks at the base from too much twiddling around. Once the boards are stable on a box I plan to add an SMA and an antenna, which I think is going to be an adventure on itself...

Tried the voltage follower (although, I do not understand why it works, which is bad) and it worked as described. Got the reference voltage minus 0.7. But boy did the NPN heat up when power was going through (that was at 9V). When I went to the shop to ask around for a Power NPN and a heat sink,
yes, you definitely need a power transistor if there's so much current it's getting hot.

Quote
they recommended instead a voltage regulator fixed at 3.3V, together with a heat sink. It wasn't really expensive, so I went with that too (LM 1117T-3.3 http://www.ti.com/lit/ds/symlink/lm1117.pdf). Tested it and it works, 800mA is more than enough for the two relays. On the PDF there are some reference circuits using two condensers (a 10uF and a 100uF) on the input and output, connected to the ground. I guess the condensers keep the input and output stabilized.
This will work, but consume more power than a voltage follower when the relays are off.
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At this point I have many questions. Is a voltage regulator just a voltage follower with a diode somewhere to tune the reference voltage and some heat protection? I have seen some diagrams on voltage followers on the internet and they all include a zener and some resistences to tune the reference voltage. Maybe a regulator is just a voltage follower with all these things packaged.
No, these are not the same thing, although some voltage regulators use voltage followers.  The VR is much more sophisticated at keeping a constant voltage output, but this comes at a price - the quiescent current when there is no load.
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Otherwise, is there any pros or cons on using one or the other?
see above.
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The other question is: does the voltage follower (an NPN, maybe with a heat sink, with base connected to Vref, collector to the Vin and emitter as Vout, being Vout = Vref - Vd) have any other components involved (resistors maybe?).
No other components are necessary (other than an heatsink). Since the load is directly connected to the emitter, the emitter will 'follow' the base voltage - 0.7v diode drop, with the current controlled by the gain of the transistor.
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I want to know more about this circuit, it looks really useful. All things I found on the internet about this have zeners and resistors to tune Vref.
get a good tutorial or book on transistors - they are fascinating and, despite having BILLIONS of transistors in our circuits, there are times when a single transistor can be useful.
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Attached the current revision of the 'master' board.

Well, it's 'close', but your diodes D1 & D2 are doing absolutely nothing in your circuit.  Are you sure the circuit diagram is accurate?  The diodes are supposed to be across the relay coils.

Tom

perky

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Re: Moteino, 4 AAA 1.5V batteries and two relays
« Reply #19 on: March 13, 2017, 06:32:29 PM »
Well I don't see the need for the regulator at all if you can use 9V versions of the 36.11 relays e.g.:
http://www.ebay.co.uk/itm/36-11-9-009-4011-Relay-electromagnetic-SPDT-Ucoil9VDC-10A-250VAC

In fact that's far better as you will reduce the current through the relay compared to the 3V version by a factor of 3 and not waste any power in a regulator.

Mark.
« Last Edit: March 13, 2017, 10:16:30 PM by perky »

chspter

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Re: Moteino, 4 AAA 1.5V batteries and two relays
« Reply #20 on: March 14, 2017, 08:31:31 AM »
Well I don't see the need for the regulator at all if you can use 9V versions of the 36.11 relays e.g.:
http://www.ebay.co.uk/itm/36-11-9-009-4011-Relay-electromagnetic-SPDT-Ucoil9VDC-10A-250VAC

In fact that's far better as you will reduce the current through the relay compared to the 3V version by a factor of 3 and not waste any power in a regulator.

Mark.

If alkaline batteries show depletion by lowering their working voltage, wouldn't that make the relays to stop activating when the voltage is lower than their working limits of operation?

No, these are not the same thing, although some voltage regulators use voltage followers.  The VR is much more sophisticated at keeping a constant voltage output, but this comes at a price - the quiescent current when there is no load.

The datasheet on the LR1117T gives about 5mA to 15 mA of quiescent current. I measured current between the input and output pins and it gives around 13mA. On the voltage follower, I tried measuring between the collector and the emitter and I see a 0. Is that so?

Well, it's 'close', but your diodes D1 & D2 are doing absolutely nothing in your circuit.  Are you sure the circuit diagram is accurate?  The diodes are supposed to be across the relay coils.

My bad. Not accurate at all  :P

perky

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Re: Moteino, 4 AAA 1.5V batteries and two relays
« Reply #21 on: March 14, 2017, 11:35:17 AM »
If alkaline batteries show depletion by lowering their working voltage, wouldn't that make the relays to stop activating when the voltage is lower than their working limits of operation?

Well those relays have a wide working range. If you look at this spec sheet:
http://www.produktinfo.conrad.com/datenblaetter/500000-524999/503078-da-01-en-PRINTREL__12V_DC_SERIE_36_11.pdf

According to the minimum pickup and max working voltage curve (under Coil Specifications section), at 25 deg C The 9V ones have a max working voltage of 19.8V and minimum pickup voltage of 6.7V. If you allowed up to 60 deg C that changes to max working 15.3V and min pickup of 7.65V. This minimum pickup voltage might be a bit high for a depleted 9V battery which could get down to 6V (and it's internal resistance also goes up), so looking at the 6V version we get:

Max working (25 deg C) = 13.2V, Min pickup (25 deg C) = 4.5V
Max working (60 deg C) =  10.5V, Miin pickup (60 deg C) = 5.1V

So I would say use a 6V version instead, it has the lowest pickup voltage but still works OK with a fully charged battery.

Edit: BTW all I did there was decide on a max ambient temperature, read off the two values from that curve, and multiply them by the nominal working voltage of 6V to get those two voltages. I encourage you to do the same with your chosen manufacturer's datasheet for the max temperature you are likely to get because the 36.11 is a generic relay type and different manufacturers have different curves.

Mark.

« Last Edit: March 14, 2017, 11:44:52 AM by perky »