Just received one of these step down modules and have connected it to a 20v Drill battery and adjusted the output to 12v.
The 12v output is connected to a circuit that I am developing to operate relays to be driven by Raspberry pi 3B. This is only a temporary set up as the final arrangement will be connected to a 12v battery, but I am intending to use the same module to reduce the 12v down further to give 5v output to drive the Pi. This part of the circuit is not connected yet.
My problem is that when reducing the 20v down to 12v it all works as expected except that every minute or just over the unit switches off and then straight back on again, without any delay. This cycle just continues, a minute on then Off On wait a minute then off on etc.
The circuit is just a collection of relays and LEDs, nothing fancy, no timers or anything like that. The current draw on the output is only 0.5 amp.
The step down module does not seem to do this with no load but it is very difficult to notice if it does or not. When connected to a single automotive 40 amp relay drawing about 0.15 amp it also switches off and on at about 1 minute.
Would appreciate information whether this is inherent to the unit or is it faulty"
regards Max Lowe
Hi Max.
That device has current limiting. It is probably set border line and going into current limit in which case the voltage will reduce until an equilibrium is reached then the voltage may be too low for the relays to hold in.
The adjustments are multi turn pots as you must have found out by adjusting to 12V. Turn the current pot clockwise (possibly to the end) and you will probably fix the problem.
The procedure for setting if current limiting required, if not leave it at maximum:
Set the required voltage with output open.
Adjust current pot to minimum. A faint clicking sound will be heard when this point is reached. It ratchets over the end, you are not doing any damage.
Insert some sort of current meter across the output, This will be almost a short circuit but is OK.
Advance the current setting pot until the desired limit is reached. The voltage will remain almost at zero while this is going on but that is normal.
Switch off, remove the current meter and you are set to go.
Happy adjusting
Cheers Bob
Bob,
Thanks for the quick reply, I have completed the turning of the multi turn pot fully clockwise and the result is the same about one minute and one second after starting every thing off then on again.
With my circuit I am able to reduce the load on the stepdown module to just 6 LEDs and it still happens with the LEDs just dimming right at the one minute one second mark. I am totally perplexed as to why this should happen.
When I purchased the step down module I bought several and have just changed module and with the new one straight out of the packet the same thing occurs.
Regards Max
Hi Max
That is a worry.
This only leaves the 20V supply you are using. There might be something funny about that. Can you find another primary supply to try. It will have to be more than 14 or 15V. Like 2 x 12V batteries in series (24V).
An oscilloscope would be useful here. A DMM won’t be anywhere quick enough to observe any short term problems.
When you are using relays you do have a diode across the coil don’t you. Some relays have these fitted so making the coil connections polarity conscious. I don’t quite see how this could have damaged the converter but just clutching at straws. It is pretty good practise to fit diodes anyway, needed or not.
There is no circuit provided for this device (or none that I can find) so can’t see if there is anything funny there. Can’t see how there would be though as others are using these with no apparent bother (except not realising the pots are something like 20 turns). So this gets us back to your primary 20V supply.
Cheers Bob
EDIT: What is the LED doing while all of this is going on. What is the colour if it is on, if all well it should be green or off.
Bob,
Thanks for your input and help.
Connecting 2 car batteries in series gave me about 26 volts, it took a bit of fiddling to connect them in series and to the step down module, thought I would have to readjust the voltage but no, volt output was just over 12v. The unit worked perfectly without the off / on hiccup at 1 min. So you diagnosed the problem perfectly. The LED was on green the whole time.
I never would have thought there would be a break in the supply from a 20v lithium drill battery every minute.
Thanks for assisting
Regards Max
Hi Max
Pleased to see problem solved. Thanks for wrapping the post up.
I have stated before that using power banks and other sources designed for something else can be fraught with problems. You had presented the drill battery with a different load and you never know what clever bits are in the battery pack. It apparently shut down for a short period with the load you presented but works perfectly in the application it was designed for. Also there are often more than 2 connections on these batteries. Never did find out what the others are for. You did use the correct ones did you not???.
Never mind. Problem solved. Put that battery back on the drill and leave it there
Cheers Bob
