Today, let's see what's inside the protection box of the donated Utrai 12V 2500A peak car jumpstarter. Previous episode: • Utrai 2500A Car Jump S... Please support me on Patreon: / diodegonewild Instagram: / savage_danyk
I also expected a bank of mosfets to do the job. Relays are very handy but mosfets are better, no contacts to spark and go bad. The car looked very happy :-D The cat didn't look too interested, no change there lol.
yes, several mosfets in parallel would be a better solution. They could switch way more current without taking as much space. But they are probably more expensive and there's still the problem with the reverse diode...
@@AKAtheA I have abused many relays for fun, and the only times i have seen them fail open, is with massive overload, where the contacts melt away. In a slight overload situation it is actually very common for the contracts to stick i.e failing closed.
A very popular Tacklife jumpstarter also contains the same 70A relay. I was called upon to try to repair one that would not charge. It had been overused/overheated and the Li-Ion cells had leaked resulting in the positive connection lead to the pack corroding and falling off. The relay was fine.
Would love to see more on DC to DC converters. Particularly 12V - 300V+ as trying to make a DC capacity discharge ignition system. At the moment just trying to modify a purchased module to do the capacitor charging bit but would like to make my own.
simple solution for 8:10 is to implement an ideal diode configuration using two MOSFETS with opposing drains. Provides space savings, reduces complexity and eliminates contact wear.
It would be interesting to see just how many Amps it actually takes to start a car in a typical situation (connected to a flat battery unable to turn the engine over and allow time from connection to walk to start the car and typically crank for 4-5 seconds) monitoring voltage (at pack and at starter) and current through out, I might attempt this myself.
Could you please make a video about your Equipment/Tools and how you got your knowledge !! :D Other DiodeGoneWild-Fans may upvote/like this so we all can learn something ! Thank you AND More Salt !!!
No chance. If you believe that than you'll also believe the 100milliohm contact resistance; at 70A the contacts would dropping 7 volts and be dissipating almost half a kilowatt of heat.
@@ferrumignis Believe what? The current marked on relays is always switching current. That's why there's often two separate values given for ac and dc.
@@ferrumignis lol, it's obviously not 0.1 Ohms. Datasheets for 70A automotive relays list initial voltage drop @ 10A 10-20 mV. So 1-2 mOhms. Also that power pack will not deliver 2500A, you'll be lucky to get 500A based on capacity of the lipo.
Google "Ideal diode mosfet circuit" and you'll see some circuits with 2 x P-MOSFET connected back to back in the + supply path. You'll also see 2 mosfets in a TP4056 Li-ion cell charger/protection modules, they're used to cut off the connection to the battery, if an Over Current (OC), or And over voltage (OV) conditions occur. The reason they didn't use a MOSFET instead of a relay, is no MOSFET can carry that much current, even for a short time. Using a beefy enough industrial transistor would probably cost hundreds.
Glad I'm not the only one who is enthused by cheap oscilloscopes. I have a Tektronix 2230 100mhz but there's something about these cheap scopes that keeps bringing me back for more.
Why is the relay intermittent on and off? Is this to prevent the relay from turning on under full load? Maybe the controller senses the switching of the in car relay (voltage drop) and only turns the relay in the car jumper starter on when the car start relay is off (so the car jumper starter relay is not switching full load)..
If that relay tries to break in an actual scenario to prevent backfeed, there is likely to be arcing across the contacts due interruption of high currents.
Just did the math. 8 awg should handle 250 A for about 11 seconds if it can withstand a 50C temperature rise. Probably good for 22s if we assume 90C rated insulation and a battery that failed due to the cold. the 2500A "rating" is probably the short current, or just some random number to imply its stronger than a brand new, room temperature, truck battery.
@@deltab9768 awesome, thanks! I just picked the 250A out of thin air but pleased to hear it's in the right area of guesswork! I know I've melted 35mm2 cables (2AWG?) with ~7-800A.
Chinese manufacturers usually rates battery short circuit current to be more impressive , but propably the 2500amps if its even possible is for very brief moment when the starter coil is charging. I think 200-300 amps at max for few seconds is the maximum current of the battery, but once the starter is rotating the current dont need to be more than that.
@@bmvfabrika8148 Yes. As far as I can tell the reason car batteries are 500-1000 CCA is to account for some wear and tear before needing to be replaced. If this thing can give 350A for 5 or 10 seconds, that is probably more than adequate.
well, they definitely don't fully charge it, but even just a little surface charge allows the lead acid battery to supply a short pulse of high current. Even a very little extra charge reduces the internal resistance by orders of magnitude.
From what ive seen these things tend to fail/explode after a few uses , It may just be for light use as in dont use it to jump a car thats battery is completely 0v , I use a jump starter that has super caps in it.
Just looking at the gauge of the jumper wire it will become a hot resistor dropping the voltage at 2500 amps. Under load voltage can not drop below 10.5 volts. Amps will go up at lower volts but not do work just become heat making higher resistance in the Circuit.
My understanding is the battery voltage is allowed to dip to 7v when starting. But yes, the wire can't really handle 2500 amps. 2500a is the calculated current needed to melt 8awg wire in just 1 second.
@@eDoc2020 in automotive all the ECM‘s and the PCM‘s and body control modules start dropping out below 9.5 V. Even back in the 60s and 70s prior to any computers when testing the battery on starting cranking voltage did not allowed to go below 9.8 to 9.5 V 10.5 V was considered excellent and extremely good
@@coldfinger459sub0 Perhaps, I was going by the Cold Cranking Amps definition of 30 seconds before going below 7.2v. I suppose that really isn't representative of any real-world situation, though.
@@eDoc2020 you are correct cold cranking amps have nothing to do with the real world. But still think of it if you allowed 7.2 V at your cold cranking amps it would still not start. In what happens as the voltage keeps dropping the ants go up the motor doesn’t turn so the motor windings heat up and when you heat up the copper windings the resistance goes up and makes it draw more amps in a repeat the cycle until burn up if you were able to hold your finger turning the key without letting it off. But of course most people know better and stop turning the key when the motor doesn’t turn anymore. But in my younger years as a teenager in through my 20s I have seen customers hold their key in the cranking position until smoke started coming out of the windings of the starter and it would burn out.
That relay contacts will stuck after couples of starting events.. because the negative side of the battery is already connected. So when the relay contacts closed there will be full current running through those contacts. And normally relay contacts are not connected properly.
The relay does NOT turn on the starter. It turns on when you connect it to the existing car battery. In those cases it should always be well below 70A. When the starter runs, the relay acts pretty much exactly like the wires that connect to the car, it is just a passive metal conductor.
@@eDoc2020 Yeah I guess, but then most cars have the control for the starter not in the same place as the car battery. :) So unless you have 2 or more people using the device AND dont follow the instructions, it should be impossible to mess this up.
It would be interesting to draw a controlled current from the unit, say 1A, and measure the voltage across the relay. That would show its real resistance.
There seems to be some trolls who always dislike such videos. The usual suspects: Group A: - Why is your accent funny - Why do you speak like that - I don't understand your english - It's pronounced "xyz" Group B: - They don't understand what he is talking about For Group A: where is your RU-vid channel where you speak flawless english (Queen's english not Murica)? Can your channel survive without you begging for likes/share/subscribes? DGW doesn't and he still puts up quality videos without the begging and constant reminders to subscribe. For Group B: Search for life hacks on RU-vid. You are better suited there
Works so-so before, due to metal components of the unit.Probably doesn't work while starting and might well not work afterwards either. It might be magnetized top to bottom at that point...
That protection box MUST have much bigger task, it is only thing what protects your car from over voltages. 16.8VDC is insane high and can damage the car, especially the modern ones. It could helps to protect little if it sense the cranking and triggers the relay only for that moment. Still, super dodgy and super dangerous product. If that "fancy smartphone power bank" could deliver 2500A, this relay can explode :P Even that 70A label there is highly questionable, possible it is the peak value only. And why people need the jump starters? Fix your car if it need too much jump starting, buy new battery, turn off some power hungry accessories and drive longer distances. It is not bad idea to charge the battery by battery charger if you can not to do anything above. If you do not planning to drive by car long time, use battery maintainer or disconnect battery. Yes that last part is bit questionable because even that simple thing can destroy the car... I do not understand what the car engineers smoked before they designed the modern car electrical systems... Ok, disconnection does not damage but inrush current on connecting can damage. Easy way to limit the inrush current is by resistor or car test light (incandescent bulb only, not the led rubbish) before the negative terminal re-installation. It helps to recharge the all car capacitors slower and no inrush current damage.
2500A is probably very short term. A typical car takes 500A max at startup, and even that's short term. The rating of the relay is also probably continuous so it should handle those peak currents.
Maybe small cars in europe, 500 amps is on the lower side of what I usually see here in the states. Even the cheapest car battery will put out over 500 amps for short bursts.
The starter relay in modern cars is usually only quite small if it needs one at all, capable of at most a few tens of amperes to have a safety margin, with some back EMF protection (if you're lucky). It, or the key switch directly activates the massive solenoid/relay built onto the starter motor itself, which both mechanically extends the bendix gear to mesh with the starter ring gear, and connects the main starting current of hundreds of amperes to the motor windings. There are so many different types of engines, starters, etc; geared or direct drive, and different environmental and maintenance conditions, that it'd be really hard to get an average current, but initial crank is towards 200A, and continuing turn over is 70 to 100A for smallish well maintained engines in warmish conditions.
@@Tekwyzard Thanks for the response. Question remains; what is the current limitation/rating (initial and sustained) for the contacts in the relay on the starter motor? (This is the relay i meant in my initial remark/question.)
I would never buy or carry a time bomb like this in my car. Imagine leaving a fully charged one in the car and the outside temp drops to -30ºC and the electrolyte freezes and bursts the membrane and you'll have an explosive lithium fire! Good luck putting that out. Fire departments are struggling with lithium battery fires like those on a Tesla EV. An honest mistake that will cause a fire and burn down your car! A good design would be like used in EV cars. When the temp drops bellow zero, the computer uses the power from the battery, to keep the battery from freezing. This self-heating will eventually drain the battery and a drained battery can freeze all it wants. It will not be usable anymore, but it won't be a fire hazard either. I live in Canada, and I have to think about temperature.
the diode inside the mosfet is drawn the right way. The mosfet is meant to be an overdicharge/overcurrent/short circuit protection. It doesn't protect the jumpstarter battery from being charged by the alternator.
I just calculated that, funny enough. Probably 150-200msec at that current, by then it will read "SC" and open the relay, burning the contacts on the way.
All of those lithium jumpstart packs are garbage. They will never start a truck or SUV. If you are lucky they may start a bike or a lawn mower. You need a jumpstart pack with a big sealed lead acid battery if you want something that will actually work. They don't need any fancy protection that drops half your voltage under load.
It would be interesting to see just how many Amps it actually takes to start a car in a typical situation (connected to a flat battery unable to turn the engine over and allow time from connection to walk to start the car and typically crank for 4-5 seconds) monitoring voltage (at pack and at starter) and current through out, I might attempt this myself.
