No rating on wire. Want to use with DC bench - Page 1
Forum section: electronics / beginners

author: renzoms
author_rank: Regular Contributor
timestamp: December 12, 2021, 06:03:28 pm
content: Needed a banana plug-to-X or alligator clip-to-X so I could use my DC PSU terminals (+/gnd/-, so I could get split supply).I only have 2 banana-aligator wires (the ones that come with the supply)So I found these alligator-alligator clips at autozone that I could “brute force” a connection.No rating (current/power/gauge) so idk if these will be safe to use with my 30V supply.Might go to home depot/micro center.Thanks for your help

author: bob91343
author_rank: Super Contributor
timestamp: December 12, 2021, 06:23:11 pm
content: Those will work up to an Ampere or so.

author: TimFox
author_rank: Super Contributor
timestamp: December 12, 2021, 06:24:45 pm
content: Looking at the photo, myguessis that the wire is AWG18 or equivalent. For safety regulations, that would be good for several amperes. More important might be 0.02 ohms/meter, depending on your application. Any wire that looks like that in the photo has sufficient insulation for such a low voltage (30 V), but the non-insulated alligator clips need to be handled safely. The voltage rating of wire is only a function of the insulation, and the current rating depends on the wire size (copper) and its environment (free air, in conduit, in cable, chassis wiring, etc.).However, you have given almost no information to receive a useful answer.1. How much current do you intend to run through the wire?2. Normally, the label on such a product would give the wire size. Did you look?3. How are you "splitting" the PSU connections? A single power supply usually has + and - connections, with a third connection for the chassis that isnot connected internallyto either output. This allows you to ground either (but not both) output connector to obtain either a positive or negative output with respect to ground. Splitting it into, for example, +15 V and -15 V requires external circuitry.

author: renzoms
author_rank: Regular Contributor
timestamp: December 12, 2021, 06:54:37 pm
content: TimFox,I see. The non-insulated alligator clips could shock stuff.Thanks for the information.The max current I would run through the wire is 5V.I looked all over the box. Nothing on it. Maybe the wire size is on the insulation, but I left it at the store.I mean I am splitting the PSU by connecting this green GND terminal to the ground bus on the breadboard, then connecting the red + terminal to the positive bus on the breadboard, and then connecting the black - terminal to wherever I need a negative voltage supply (i.e. powering an op amp.) You can see these colors and terminals in my pictureI should add I wanted to do this because I was getting bothered by the slight difference in the split supply voltages I produced with an op amp.+15V and -14.5V using a sort of buffer op-amp (LM741) to create a virtual ground reference point, from which I could get positive and negative voltage supply (from my PSU), to the power my (other) op amp. You can see this in the photo.So I made some measurements (voltages and resistances), and started looking at offset voltage, input bias, and was going to start experimenting through this op-amp and other circuits, most likely starting a new thread (with schematics and pictures and well written questions).So I'm in between a few experiments/threads right now and it's going to take me a few days to get on my feet/comfortable with the lab.Thanks.I should add I am going to start streaming from my lab, giving interested forum browsers the access to hop in and chat with me using some sort of voice chat. From my point of view that opens up the door for some great advice while I work out my first circuits and experiments of real (non-ideal) functioning circuits.

author: BrokenYugo
author_rank: Super Contributor
timestamp: December 12, 2021, 07:05:54 pm
content: These are automotive test leads for shoving ~12V wherever one wants to (expecting a low current draw) for troubleshooting purposes, 1 amp isn't a bad guess.For most bench supply purposes, if one of paying attention the the supply voltage at the circuit under test, you'll have voltage drop problems long before you have wire insulation melting problems. That said, if you're curious, it sounds like you have a bench supply, set it something like 100mA and a few volts, short the supply with the lead in question and measure the voltage across it, from there it's just ohm's law to get a rough idea of the resistance of the wire and a current limit that gives a reasonable voltage drop.Many people make their own dedicated PSU leads with heavy gauge silicone insulated wire (very high strand count, short lengths reasonably priced on ebay) and solder on their own ends suitable for the task (avoid the cheap no name banana plugs).Also, as TimFox points out, you can't split a single channel supply like that, the earth is only provided for earth referencing one end, it isn't connected to a midpoint so it cant be used as one.

author: renzoms
author_rank: Regular Contributor
timestamp: December 12, 2021, 07:13:14 pm
content: BrokenYugo,Thanks!Okay. Fortunately I found a nice split-supply circuitAnd we (I) got over this circuit (hurdle).

author: bdunham7
author_rank: Super Contributor
timestamp: December 12, 2021, 07:24:17 pm
content: https://www.dormanproducts.com/p-10191-85654.aspx22AWG, probably PVC insulation. Ok for low power bench stuff, but I wouldn't use it on an automotive circuit. I might use them if I had them, but I wouldn't pay money for those.

author: james_s
author_rank: Super Contributor
timestamp: December 12, 2021, 07:27:40 pm
content: You could just build a dedicated split supply for op-amp circuits, +/- 12 or 15V would be typical, using 3 terminal regulators. It's a classic beginner project, fairly easy to do and useful to have around.

author: TimFox
author_rank: Super Contributor
timestamp: December 12, 2021, 07:38:52 pm
content: You didn’t answer the question about how much current is either required by your load or possible with your 30 V power supply. (“5 V” is not a correct answer.)The splitter circuit you show should work, but be careful with currents. The op amp output must be capable of sourcing or sinking a current greater than the difference between the positive rail current and the negative rail current.

author: renzoms
author_rank: Regular Contributor
timestamp: December 12, 2021, 08:05:37 pm
content: Thanks bdunham7Thanks james_s. I built one using an op-amp and using it's output as a virtual ground. I'm not sure what you mean by 3-terminal regulators, although I do own some IC Regulators (Lin Pos/Neg ADJ), whatever that meansI will keep this in mind in any case.TimFox, I meant 5 A. Not sure if you're talking about the op amp used to produce the split supply, or the op amp I'm powering with the split supply.I wonder, are you advising me to check the output current of this op-amp to make sure it does not exceed it's max output current? I did not think of that, I just assumed it would be fine. Well, now this is a GREAT reason for SPICE holy heck. TimFox, I'll be starting a nice new thread that will be using this circuit, I'll edit the reply here and link it fyi. Thanks. Edit:https://www.eevblog.com/forum/beginners/op-amp-imperfections-sine-wave-generation-and-linear-transistor-amplifier/new/#new

author: TimFox
author_rank: Super Contributor
timestamp: December 12, 2021, 08:24:30 pm
content: The splitter circuit will work well to produce a bias voltage for a virtual ground in the main circuit, but if the main circuit needs to put out several amperes into a load connected to ground, the load current into ground needs to pass through the splitter’s op amp output.I have seen this type of circuit used successfully for multiple op amps in signal-level dc/audio analog processors (such as a phase meter), where the amplifiers drive medium impedances (say, 1.0 to 10 k), so only a few mA need to be sourced/sinker by the splitter.

author: radiolistener
author_rank: Super Contributor
timestamp: December 12, 2021, 08:27:36 pm
content: Quote from: renzoms on December 12, 2021, 08:05:37 pmTry to measure wire resistance. If it's about 0.02 - 0.04 Ω, it is ok for 5 Amps. You can do it with lab PSU, just connect wire between + and - and put 4.000 Amps to it. Then measure voltage drop on the wire. Resistance = Voltage / CurrentIt looks that it has some insulation damage, so be carefulif you're still looking wires for 5 Amps, I would recommend these Chinese wires:https://www.aliexpress.com/item/32785850472.htmlThey have about 0.016 Ω and works good for 5 Amps.

author: james_s
author_rank: Super Contributor
timestamp: December 13, 2021, 05:36:37 am
content: A 3 terminal regulator is something like the classic LM7805, they're called that because they have 3 pins. A 7815 for positive and 7915 for negative are a typical combination. Note that the 79xx negative regulators have a different pinout than the 78xx positive regulators. There are many similar parts on the market today.

author: wizard69
author_rank: Super Contributor
timestamp: December 13, 2021, 09:11:05 pm
content: Quote from: renzoms on December 12, 2021, 06:03:28 pmThe ultimate answer here is to go on line and buy some test leads that properly do what you need. If not test leads the components to actually build your own. Frankly the online vendors are about your only choices anymore.Now given that we all have budgets sometimes buying just isn't going to work. This is a good time to consider salvage of wire. Hopefully your binding posts have the ability to clamp wire.QuoteI often associate "brute force" with being stupid (been there done that and frankly have seen worse done by others). You are far better off making sure something will work based on the technical details of whatever you are doing. It doesn't matter if you are building your next electronics circuit or welding a trailer together, you can't forget engineering.In this regard you need to find out how wires handle current and what is acceptable for the installation. In some cases voltage drop across a wire can be significant impacting the size of the wire required.QuoteIt is highly unlikely that voltage is a problem here. The insulation on most wires will not break down at 30VDC. What is a concern is heating of a wire and its insulation due to current flow. Later on you mention 5 amps (you need to get current and voltage straight) which probably isn't a problem here, but I can't tell the wire size from the picture. By the way are you even sure your leads supplied with the power supply are heavy enough?QuoteDon't go anywhere until you know what you need!!!!! Also there is a difference between what you can do on the bench and what you can do other locations. A product or installation has to meet standards that a bench project or experiment does not have to meet.In any event what I mean here is to avoid buying blindly but instead figure out what you need before shopping. This applies to test leads also, many test lead offerings on the market would be marginal, at best, at 5 amps. You will likely need between 18 and 16 gauge wire.QuoteNo problem! Just slow down. The wire you purchased may be fine but the insulated alligators are a no go. Honestly I wouldn't even use them for auto work. This just highlights that there are multiple concerns that you need to address when buying almost anything for a project.

author: james_s
author_rank: Super Contributor
timestamp: December 13, 2021, 09:58:51 pm
content: For clip leads and such after dealing with cheap crappy ones that had a high failure rate I started making my own. I buy decent quality alligator clips and banana plugs from DigiKey and 18awg silicone insulated wire in various colors from hobby companies that sell RC cars/boats/planes, it's very flexible and can carry a lot of current without burning up.

author: bdunham7
author_rank: Super Contributor
timestamp: December 13, 2021, 10:03:44 pm
content: Quote from: renzoms on December 12, 2021, 06:03:28 pmMicrocenter is OK in a pinch, but if you are going to be an electronics hobbyist you should become familiar with mail order places. Start here:https://www.allelectronics.com/