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Relay switches off on a too high supply voltage on the power rail (12 V or 24 V)



Circuit with a Schmitt trigger where a relay switches off on a too high voltage on the power rail. Switching without any doubt or strange “typical switch effects”.

Developed for 12 V or 24 V lead acid battery chargers. Set the “drop off” voltage with P1 (the 10 K potentiometer, critical aligning). Integrated in my solar panel charge circuit that charges a 24 V – 75 AH battery out of a 45 Volt max 5 Amp solar panel.

Earlier published, but with a flaw (I forgot the 220 K resistor….), so the earlier publication on YT was deleted. Thanks to YT user “mark sk”.

Many of the videos hat I have published on You Tube can be found via my Channel Trailer: Link is

In thematic order you can find these video’s under the “comments” section.

Important: to find all the links to the (+/-700) video’s on my YT Channel, select, in the comments section, “NEWEST FIRST”

A big bunch of links (only links) to my schematics (445 links to You Tube video’s) are published in this booklet

on the LULU website (cost 2 Euro’s)

All my books about electronics are available via the website from “Lulu”, search for author “Ko Tilman” there.

Link is https://www.lulu.com/shop/search.ep?keyWords=ko+tilman&type=

My books are also available via Barnes and Noble and via Amazon.
Regarding all my video’s: I constantly keep them actual, so the original video’s with the most recent information are always on YouTube. That is the source, and search there. When my video’s are reproduced or re-edited on other websites/channels you can not (!) be sure about the original content (=really working electronics) and important adaptations to the circuits.
Be aware of that, I saw on the internet many of my circuits reproduced in a poor or even not proper way. I can not help that, sorry. Upload 24 september 2018.

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Lead acid car battery charger with automatic switch off between 13 and 14,5 volt (schematic)



Sorry: the video stops suddenly due to a low camera battery, but everything was told so far.

Schematic & demo of a lead-acid car battery charger that automatic switches off on the following battery voltages (set with a 3 pole switch): 13,23 Volt / 14,18 Volt / 14,50 Volt. That switch-off voltage depends also on the (use) of a diode to the battery. But surely a safe switch-off voltage can be set, e.g. in the middle position of the switch. After testing with the “computer diode” (barrier voltage 0,6 Volt) the circuit did not want to switch off at the highest voltage (14,5 V). Anyway: it switched off properly at the middle voltage (middle switch position, 14,2 V).

It is not a beginners circuit because you can damage your car battery when you let it switch off on a too high voltage and the aligning to the different voltages must be watched carefully and takes time.

Plus the fact that the resistors that decide about the switch-off are in the (very) low resistance range. So it could be that you must experiment with resistors in the 5-20 Ohm range to precisely get your switch-off moment with lead-acid batteries with slightly different properties, compared to the ones that I used.

By the way: I used 2 different lead-acid car batteries (40 Ah and 75 Ah – 12 Volt) during my experiments and all worked fine, so too much worries are not necessary.

You could get e.g. an old 12 V car battery for free in the dump and do your experiments in the precise aligning process. Of course that battery must be a little bit healthy, with a “dead” lead acid battery it is not possible to align everything properly.

The basic alignment can, by the way, be done without a lead-acid battery connected to the circuit. It can be done by connecting a + voltage (opposite to ground, minus) to the sense-line and very very slowly adding voltages via a separate power supply between 12 V and 15 Volt.

At the same time: connect a Voltmeter with 2 digits behind the comma (so 1/100 Volt) to the sense line (+ opposite to ground, minus) see and align when the Schmitt trigger switches off. When all is OK you will see that the Schmitt Trigger switches on very precise (1/100) voltages in this range (12-15 Volt) and this depends on the setting of the 470 K potentiomer.

Align that 470 K potentiometer carefully (going out off the middle position, slightly up or down) till you find the right 3 voltages where the charger switches off.

By the way: it is not difficult. The circuit works very properly and was thorough tested during the development the past weeks.

Be careful with 110 V or 230 V AC, it can be lethal. Make it impossible that you, during experiments, can touch a 110 V or 230 V wire by isolating all these wires properly with good quality PVC tape (preferred Coroplast tape) and/or blank silicon kit. Use tiewraps to fasten PVC tape isolations, it can slide off.
All the videos hat I have published on You Tube can be found via my Channel Trailer: Link is

In thematic order you can find these video’s under the “comments” section.
Important: to find all the links to the (+/-700) video’s on my YT Channel, select, in the comments section, “NEWEST FIRST”
My books about electronics are available via the website from “Lulu”, search for author “Ko Tilman” there. Link is https://www.lulu.com/shop/search.ep?keyWords=ko+tilman&type=
My books are also available via Barnes and Noble and via Amazon.
Regarding all my video’s: I constantly keep them actual, so the original video’s with the most recent information are always on YouTube. That is the source, and search there. When my video’s are reproduced or re-edited on other websites/channels you can not (!) be sure about the original content (=really working electronics) and important adaptations to the circuits. Be aware of that, I saw on the internet many of my circuits reproduced in a poor or even not proper way. I can not help that, sorry. Upload 22 August 2018.

Important: you can omit (bridge) the diode to the battery. It will switch off more easily, because the diode gives a voltage drop.
The problem could be that the “charge” led keeps lighting up when the circuit has already switched off.
…..
(“from” = “of”, sorry Dutch way of saying)

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