Car lighter adapter - Page 1
Forum section: electronics / repair

author: psysc0rpi0n
author_rank: Frequent Contributor
timestamp: August 18, 2018, 01:29:29 pm
content: Hi.I have this cooling/heating box/cascan/refrigerator that keeps food and beverage cool or hot that you take to camping you know? I don't remember it's name in English.Anyway, this one I have can be hooked up to the car lighter and the cable have a small circuit at the car light end of the cable.This small pcb is like burned out and I wanted to try to figure out which component got burned. The only components it have are:3x 1N4001 diodes1x 3V6 zener1x ~300 ohm resistor1x NPN H1061 transistor.Attached are a couple of pictures of the circuit.The visible connections, if I'm not mistaken are like the 3rd picture attached.Both 1N4001 are outputting a voltage in multimeter of about 0.48V when I select the diode mode on my multimeter. I compared with a 1N4007 I have here and that I know its OK and it outputs about 0.5v. Zener outputs about 0.67v.I'm not sure I can test diodes like this with the circuit off and with no load.Can you guys suggest anything?What is this circuit used for? To bump up the car lighter voltage to 12v which is the required voltage for the refrigerator to work?Enviado do meu SM-G935F através do TapatalkI attached the outer casing of the adapter.

author: sokoloff
author_rank: Super Contributor
timestamp: August 18, 2018, 01:33:47 pm
content: Visually, it looks like at least the transistor burned.

author: psysc0rpi0n
author_rank: Frequent Contributor
timestamp: August 18, 2018, 01:54:01 pm
content: Quote from: sokoloff on August 18, 2018, 01:33:47 pmThe transistor, visually lloks like the best of the components. I removed it and replaced by 3 wires just to help me figuring out the connections..I'll upload a picture of it attached to the "sink" they used in a minute!

author: Ian.M
author_rank: Super Contributor
timestamp: August 18, 2018, 01:55:37 pm
content: The label says all:QuoteIts a crude linear regulator outputting 3V. It cant output more than that because the transistor is an emitter follower with its Vbe subtracting from the Zener voltage.The 1N4001 diodes drop approximately 2V, reducing the max input voltage of 14V to 12V at the transistor. With 9V drop across it, it, at max current it dissipates 5.4W so no wonder it cooked itself without a decent heatsink.I wouldn't bother fixing it. Get one of those 3A buck converter modules off EBAY, set it for 3V out, and lock the adjustment with a dab of nail varnish. Wire it into the lighter plug housing, with a beefy 20V unidirectional TVS diode across the module input to protect it from spikes, and a 1A fuse in front of that.

author: psysc0rpi0n
author_rank: Frequent Contributor
timestamp: August 18, 2018, 02:05:52 pm
content: Quote from: Ian.M on August 18, 2018, 01:55:37 pmI think the label says Output DC 15V 600mA.Anyway, I can't do that because I'm leaving for vacancies today. The best I have here at home is a couple of BC547, BC548, BC557 and BC558 which cannot handle these currents. I'm going out for a Chinese shops to see if I can find something with the same specs just to work it around now pretty quick!

author: Ian.M
author_rank: Super Contributor
timestamp: August 18, 2018, 02:46:33 pm
content: Its impossible for it to output 15V - as there is no inductor or chopper chip, there's no way for it to boost the 14V of a typical running 12V vehicle supply to 15V + there must be at least 2V drop in the 1N4001 diodes if there are more than a few mA load current, so even with a higher voltage Zener fitted, you wont get more than 12V out.Here's the transistor datasheet:http://hardware.speccy.org/datasheet/H1061.pdfYou should be able to find something similar - I'd look for a TO220 NPN rated for >30V and >3A with a HFE@1A of around 100. However it will probably cook itself again sooner rather than later.

author: psysc0rpi0n
author_rank: Frequent Contributor
timestamp: August 18, 2018, 02:54:46 pm
content: Indeed. Its 7.5V.I found these in a Chinese shop.Will any of them work after cutting the cables and just take the end of the original cable and soldering it to the Chinese transformer?Enviado do meu SM-G935F através do Tapatalk

author: Ian.M
author_rank: Super Contributor
timestamp: August 18, 2018, 03:09:59 pm
content: In that case, the Zener must be 8.2V, not the 3.6V you originally posted. If you want to confirm that, power it up without the transistor and measure the voltage across the Zener.The 1200mA adapter should be able to run it from AC mains. Lock the switch at 7.5V with some hot-glue and splice the wires together.However that's no help if you need to be able to run it in a vehicle on the move.

author: psysc0rpi0n
author_rank: Frequent Contributor
timestamp: August 18, 2018, 04:02:17 pm
content: Quote from: Ian.M on August 18, 2018, 03:09:59 pmYeah, no problem with the vehicle. I'll use ice to hold the stuff during the trip. When I get to destination, I'll plug it to mains!

author: psysc0rpi0n
author_rank: Frequent Contributor
timestamp: August 18, 2018, 04:43:26 pm
content: Quote from: Ian.M on August 18, 2018, 03:09:59 pmOk, problems again.I bought that chinese adapter and it has a voltage swtich that would be to supposedly change output voltage to those pre-defined values written in the adapter itself.So, voltage possibilities written are:1.5v3v4.5v67.5v9v12voutput measured voltages by my multmeter are, respectively:5.907v8.931v11.36v13.75v16.14v18.45v20.7vThe closest can get it's almost 9V. Am I going to run into problems? Shoukd I go under voltage and choose 5.9v?

author: psysc0rpi0n
author_rank: Frequent Contributor
timestamp: August 18, 2018, 05:05:47 pm
content: Well, maybe the refrigerator itself might be damaged.I tried the 7.5V on the adapter switch and connected it to the refrigerator and the output voltage max is 2.4V.This also have a polarity switch which I chosen the one on the left in the attached picture. I hope this is correct.

author: Ian.M
author_rank: Super Contributor
timestamp: August 18, 2018, 07:25:34 pm
content: It looks like the wallwart is a cheap and nasty unregulated one. The Peltier element in your coolbox will be far less efficient if there is a lot of ripple on its supply voltage. If its got any extra electronics e.g. for temperature regulation or display, you cant use that wallwart, but if its just a 'dumb' Peltier element, on all the time, simply increase the output voltage under load, monitoring the current, till you get between 7V and 8V.If you cant get 7.5V without the current going over 600mA, the Peltier element has failed shorted. If its only drawing a small fraction of 600mA at 7.5V, its failed partially open circuit - the most common failure mode for old or abused Peltier elements.If you cant get in that voltage range, go higher with one or two series diodes to drop the load voltage a bit to get it in range.Make sure the polarity matches the original supply or a 'dumb' coolbox will heat when its meant to cool or visa versa.

author: psysc0rpi0n
author_rank: Frequent Contributor
timestamp: August 18, 2018, 08:00:40 pm
content: I tried all values up to the 12V available on this adapter. Output voltage while connected to the load (refrigerator) won't go over 2.4V.The adapter heats up a bit over time and I can see a green light at the refrigerator indicating that, at least, the voltage reaches the led. But I can't feel the refrigerator cooling down. So either the 2.4V is only enough to light the refrigerator indicator led or the refrigerator is also dead.Can you explain again the diodes thing? I have a couple of 1N4007 around.Edited;The cool box has a switch that can slide to 3 different positions. Hot, Off and Cold is this matters.Enviado do meu SM-G935F através do Tapatalk

author: M4x
author_rank: Contributor
timestamp: August 18, 2018, 08:10:56 pm
content: Did you measure the current (like you've been told already)?

author: psysc0rpi0n
author_rank: Frequent Contributor
timestamp: August 18, 2018, 08:15:03 pm
content: Quote from: M4x on August 18, 2018, 08:10:56 pmNo, not the current. But is it worth it if the voltage is dropping this much?Enviado do meu SM-G935F através do Tapatalk

author: M4x
author_rank: Contributor
timestamp: August 18, 2018, 08:19:11 pm
content: Can't do any harm. Maybe there's a reason for the low voltage.

author: psysc0rpi0n
author_rank: Frequent Contributor
timestamp: August 18, 2018, 08:26:59 pm
content: Quote from: M4x on August 18, 2018, 08:10:56 pmWell, looks like it's consuming too much power. Current is about 0.9A. :s

author: M4x
author_rank: Contributor
timestamp: August 18, 2018, 08:48:37 pm
content: Quote from: Ian.M on August 18, 2018, 07:25:34 pm

author: psysc0rpi0n
author_rank: Frequent Contributor
timestamp: August 18, 2018, 09:02:48 pm
content: Quote from: M4x on August 18, 2018, 08:48:37 pmThat means the coolbox is good to go... For appliances recycling, right?

author: Ian.M
author_rank: Super Contributor
timestamp: August 18, 2018, 09:21:05 pm
content: Open it up and disconnect one of the wires to the Pelter element. If its still drawing excess current, the short isn't the element and its probably worth fixing. If the current drops to a small fraction of 600mA, then the element is bad, so its trash unless you can get a new Pelter element for less than 1/3 the price of a new coolbox

author: psysc0rpi0n
author_rank: Frequent Contributor
timestamp: August 18, 2018, 09:51:33 pm
content: Quote from: Ian.M on August 18, 2018, 09:21:05 pmAh ok. Well I have no time to open it. So I'll use it with only with frozen water bottles for the travel. In couple of hours, I'll be driving.Enviado do meu SM-G935F através do Tapatalk