* relay current Control current is 38maHi,
there are a lot of different solutions depending on what your target is:
* from rather simple
* to most power saving
* or any other optimisation
A simple solution could be
* a series resistor, and a zener across the relay coil. (shunt regulation style)
While the zener limits the coil voltage ... the "overvoltage" has to drop at the series resistor.
It consumes a lot of power and dissipates it into heat. And there no clear threshod levels for ON and OFF.
* another solution could be by adding a BJT and a diode (for protection) --> series voltage regulation.
It wastes less power, mainly on the BJT
* one could use a "switching" solution with a comparator monitoring and PWM-ing the coil current.
This is the most power saving method. It consumes almost only the relay current.
***
But as already mentioned, I guess this applicationcalls for clean threshold levels while avoiding chattering.
This could be done with a second comparator (in same package). So the circuit consumes very low power at too low input voltage, relay is OFF. Then at a ceratin point it swtiches ON the relay. Power saving.
******
Some important informations are missing:
* relay current
* how important is power saving
* how important are clean switching levels
* your target (ideas)
* your skills / what effort you want to spend (time, money)
Klaus
A resistor was my first thought. Needed to know what size. ( 1K thanks )I measure 600 ohms coil resistance in my 24V relay. It draws 40mA at 24V.
Almost a watt. By testing it pulls in at 13V and releases at 10V.
With your 65v supply you can limit current by installing a safety resistor. 1 kohm drops 40v. The relay coil is not exposed to greater voltage than its rating.
My simulation has identical relays with differing range of source voltage. Screenshot snapped when contacts are nearly closed.
View attachment 176163
Now that is a nice looking gadget.Recently found a pretty gadget that accepts up to 70VDC and delivers up to 60VDC adjustable.
----> https://www.banggood.com/RIDEN-RD60...46.html?cur_warehouse=CN&ID=6296642&rmmds=buy
Chattering is the one thing.* how important are clean switching levels Clean enough so there is no chatter
Hi Klaus,Hi
Chattering is the one thing.
* above what (input) voltage level you want the relay to be safely ON
* and below which (input) voltage level you want the relay to be safely OFF
You need to read the relay´s datasheet.
* 24V is the nominal relay coil voltage
* but the ON volage maybe is at 18V (*)
* and the OFF voltage maybe is at 9V (*)
(*) buth values are not very clean and will depend a lot on production, temperature and for sure mechanical vibration.
With additional electronics you may improve this. Like switch ON at accurately 20V (you can´t go below the relay´s specification)
(you defined it as "And when the sun comes out it’ll energize the relay" .. but you need to define it a voltage level. Nobody of us can know the level.)
.. and switch OFF at accurately 16V (both as examples)
Another thing to consider: Your input voltage is 0V ... 65V. This is a wide range. When you connect a relay, then it draws current and the input voltage my drop. How much depends on the source impedance.
Klaus
So how did you burn it up the first time?.I need some help with a 24 VDC relay that I’m trying not to burn up again.
I already have this. TS-MPPT-60Hi,
I guess you need to read how solar cells voltage and current behaves.
In short:
It rather acts as a current source than a voltage source. This means it has relatively high impedance.
* dark: zero ouput voltage, zero ouput current
* full light: specified ouput voltage at specified output current
* dark cloudy: without load the voltage is rather high, not as high as with full light. But as soon as you connect a load (relay, charger...) the voltage will drop to a very low value. This means: although the "open" voltage is hig you can´t dra much power from it.
This may result in repeated ON/OFF:
To avoid this problem the intelligent chargers/inverters don´t rely solely on the open voltage. They draw current and check how the voltage react on this.
More intelligent are the MPPT chargers/inverters. They adjust voltage as well as current to get the optimal high power from the cells.
To your system: Either you need to study how your system (solar cell voltage, current vs load and light quantitiy) .. or buy a good inverter/charger with MPPT function.
Klaus
Hooked it up directly to the solar panels. It was working for a little while, but it was getting hot, and then...So how did you burn it up the first time?.
You are apparently right.picked the 24 V relay because I thought it could handle the higher voltage, apparently not.
You don't need the diode with an emitter follower, as the negative voltage generated by the inductance will keep the transistor conducting after the power is removed, until the inductive current has dissipated.Load = your relay coil. Add a standard diode parallel to the relay coil, anode to GND
Well actually I skipped one minor bit of information.You are apparently right.
Why would you think the relay could tolerate more than its rated voltage without overheating?
The relay coil heating is proportional to the square of the applied voltage so if you applied 65V to the coil, that would increase the power by (65^2) / (24^2) = 7 times.
Components are ordered. Vielen Dank KlausHi,
simple but maybe what you want:
D1 = 24V zener
Q1 = NPN, >100V, >100mA, >2W, need to be mounted on a heatsink for 2W
R1 = 4k7, >1W
Load = your relay coil. Add a standard diode parallel to the relay coil, anode to GND
Klaus
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