Hello update on one of the items I got in my last post bag. Um, this Buck converter which is all up to 75 volts in up to 50 volts out, but 25 amps they say 600 watts and it's not terribly expensive. It's about ten dollars. So what I wanted to do today was have an updated look at this.

For example, these two devices on the heatsink are both the same, which changes things a little bit. These two resistors down here could be interesting and there's something to say about these connectors as well. So first up, the two devices on the heatsink are these things. They're Magna Chip Mdp 1991 and they are both actually the same thing Mdp 1991.

So my guess is that these, well, these are both end Channel Mosfet. So I'm guessing this is a synchronous Buck regulator. Um I Suppose you could argue that these two mosfets were in parallel, but then there's no high power diode. there's nothing on the back.

So yeah, this is a synchronous Buck converter. So you've got a series pass mosfet that most of the current is Flowing all of the current is flowing through and then you've got the low side mosfet which takes the place of the freewheeling diode. So this must be a synchronous butt converter chip. but I can't find a data sheet for it and I Know that? um, it's not one of the standard ones because they all seem to have on-chip drivers for the gate to the mosfets.

and this one the mosfet. Gates one of them is a track running down here and the other one is a track running around there. Um, they both go to these transistors which are marked to T Y which is a standard off the shelf Npn transistor. I think it's an 8550 down here.

there's a little Buck converter I'm assuming that's what it is. All of these chips have been milled so you can't see any details, but there's an inductor there next to that chip and my guess is that generates 12 volts. And the reason I think that is because this fan inside here is if the camera will focus on it, which it won't Oh yeah, there it is. DC 12 volt fan.

So there must be a fixed 12 volt power supply somewhere now. the input is I think 10 to 75 volts, 12 to 75 volts. So I'm guessing that's a 12 volt Buck regulator to power the synchronous Buck chip up there, the 16 pin chip, and also that fan. Okay, enough chat.

Let's get on with a high power test. So I've made up this little connector which goes in there so that I can put um, a high power power supply on this input side and then on the output side. I'm going to put my piece of wood with the car headlamp bulbs on it and run this up with as much current as I can. So I'm going to set this up here I'm using the power Oak power bank for this and it's got this output here: DC Output: 12 volts, 25 amps.

Well, the voltage is actually a bit higher. it's 13.4 So let's switch this thing on and I've got the Buck converter up on this little stool here. so let's turn the DC on and that should power up this unit. Yeah, the little blue light is on, so that's powered up now.

I don't really have suitable High current wires to come out of the Buck regulator and into my light bulb board here. Um, so I'm going to double up I've made up four wires with banana plugs on the end. The main problem is if you've got high current wire like this. 12 AWG stuff.

Um, you can't actually get the 12awg wire into the top of the banana plugs. So a thinner wire. it has to be right. All the bulbs are disconnected.

So I need to turn the power supply on. Is that on? Yes, that's on. Um because I need to set the voltage. Uh, why is it it's at minus 8.78 volts.

I've got my polarity right here now. I had my two Um cables the wrong way around. so I want to set this for? let's go for 13 volts because that's all I can get out of the Uh Power Oak power bank. So let's wind this up to uh okay, um, it's about a volt less than the incoming.

so I can only get 12 volts out of this. Well, let's push it right up to 12 volts. Okay, that's fine. Now let's start turning light bulbs on.

Let's start with the Um. H7s there that's actually dropped now to 11.15 volts. Let's see if I can get a bit more out of this. Now turning that pop doesn't make any difference.

Okay, let's put some more bulbs on. It's one of the H4s, so another one of the H4s third, H4 and a fourth. H4 Now the last. Reckoning With lithium-ion phosphate driving this thing, it was pulling about 17 amps.

Oh, that's dropped to 10.2 volts. Uh, let's look at the current. We're pulling our zero out the ammeter. Uh, put it around these two I think and that's pulling.

Yeah, Okay, so that's 15 and a half amps we're pulling from this power supply. Um, and it seems fine I Don't think it's even getting warm. No, it's not even getting warm. So yeah, being a synchronous Buck regulator.

Um, it does have high efficiency, so it's quite happy with 15 amps running through it. I've derated it in any case, from the 25 amps that they claim. Uh, simply because on the side of these connectors. Not sure if I'm going to get this on camera.

Possibly not. We'll have a look later, but they're rated at 20 amps. So simply because the connectors are rated at 20 amps, I've had to derate the whole unit to 20 amps. But yeah, it seems absolutely fine.

Um, there's another parameter here actually on the power bank, it's saying 172 Watts but that might include inefficiencies in the pure sine wave. No, it's not pure sine wave inverter. Is it because it's coming out of the with the DC to DC converter that's feeding that 12 volt 25 amp output on the thermal imaging camera? Um, the heatsink? It's quite difficult to get video of. It's that black square at the top because it's reflective, so all you can see on it are the reflections of the other bits.

But you can see the two Moss works. They're not even worn on a warm 40 degrees. Um, these two resistors down here are quite warm getting off of 90 degrees and the inductor is pretty warm at 56 57. Now I just wanted to, um, short out these two resistors down here I'll explain why a bit later.

So I've got this resistor. It's um, 0.22 Ohms. It's about 10 times the resistance of these down here because these are 0.02 ohms assuming they're in parallel, which I believe they are. But let's try shorting them out with this resistor.

So I'm going from the input negative to the output negative and nothing really untoward happens with the light bulbs when I do that. So yeah, I'm not entirely sure that they're going to be the problem that I thought they were going to be. Anyway, the Buck converter has passed this High current test, so let's shut this thing off. so I think this passed the high current test I Couldn't get more than 15 amps through it because that's all the car headlamp bulbs I've got at the moment.

Let's take another look or let's take a look at the data sheet for this device. The Mdp 1991 Mosfet. So this is the device. It's a Magna chip single N Channel Trench Mosfet 100 volts uh, 120 amps, 5.9 milliohms.

So it's 120 amps when you've got a V gate to source of 10 volts. Well, that should be possible on that unit. um, and 5.9 or less than 5.9 milliohms under the same conditions. a gate Source voltage of 10 volts.

Now often these things have. Oh, actually, it's here. Um, they have a silicon rating for continuous drain current 138 amps and a package limited because the pins on this package can only take so much current. Well, that's actually the 120 amps.

The package limited current is actually 120 amps at a higher temperature 100 c, but the heatsink didn't get up to that. It derates to 87. So yeah, they have the 420 amp rating and now we'll take a look at this connector. Uh, can I get the light on it? Oh yeah, there we are.

So that's rated at 300 volts. Uh 20 amp so you can see the 20 amp rating of this connector. Um I Wanted to derate this thing anyway from 25 amps, so that seems like a a suitable D rate down to 20 amps for the connector limitation. So what was I talking about when I was talking about these two resistors potentially being a problem for me? Well, this uh Buck regulator module only has voltage control.

You control it with this potentiometer. Here, you can't set a current limit, but it does have these current measuring resistors because this is a current mode synchronous Buck regulator Now I'd have to do some reading up to be absolutely certain what that means. but essentially it's measuring the current in the output as part of the feedback control. Loop So it needs to know what the current in the output is at any instant in time.

So it's measuring with these two resistors. and that means that these two negative terminals are connected either side of these resistors. and I think you can see that on the underside. there's the output negative and it's on a separate Island to the main module negative which is going across there and these two resistors here are 0 1 2 in parallel.

So actually no, in parallel, it's R05 isn't it? So my uh, 0.22 Ohm resistor is something like not 10 times greater. I think it's 20 times greater than the combined parallel resistance of these two, isn't it? So I was wondering whether it would have an effect if I bridged across these. I mean I wanted to see whether it just had any influence at all. Maybe I'll short directly across there with a piece of wire.

Yeah, let's get that set up. You see. one possible use for this thing, which I wanted to do is to use that synchronous butt converter in place of this butt converter here, which takes the oh well 25.5 volts as it is at the moment of this uh, big battery down to 12 volts for the ant minor The Cryptocurrency Miner But one idea I had was instead of using one butt converter, this runs at about 20 amps. I Think to run all four of the hashing boards at the back there.

they're all paralleled up on this little circuit board here. One idea would be to use separate Buck Regulators for each of these four hashing boards, or maybe put them in pairs just simply to distribute the load. But although these hashing boards have completely independent power inputs, they also have these signal cables which run back to this control board. Now, that means that the ground on one of these hashing boards is going to effectively be the same as the ground on another hashing board, but passed back through this signal cable, through the grounding on the control board and then back to another hashing board.

but through those signal cables. So with that, interfere with the current measuring. Now I Don't know whether this is a current mode, but regulator probably not, but would it interfere with the current measuring within the buck regulator circuit? specifically that synchronous Buck regulator. So what this is doing is it's providing a very tiny voltage for the synchronous Buck regulator to measure so that it knows what the current is in this output circuit.

Now, if you've got two of these things in parallel and you effectively connect the output of this one to the output of its neighbor, then this measuring circuit is going to get a bit of the current in this one and a better current in the neighboring unit. And is it going to get confused I Suppose the only way I'll know is to get two of these and actually sit them side by side, put some current into a couple of loads like some light bulbs, and then try to connect these two output negatives together to mix the signal from one with the signal from the other and see if they get upset. But let's just do a quick test to see if this gets upset if I actually short between these two negative points. So the latest power bank I reviewed came with this power supply which is 24.5 volts.

so we'll call it 24 volts at up to four amps and conveniently, it came with a two point. oh, is that 2.1 or 2.5 But anyway, I can plug it into the input of this Buck converter so we can run this at a slightly higher voltage. I'll get a suitable high power load on it now. So 24 volts in I've set the bulb quite dim.

The two filaments are in series, so I can put up to 24 volts into the bulb I Just want to see what happens if I short across those current measuring resistors and absolutely nothing now I Don't know what the resistance of this wire is, but it's perhaps more than 0.005 ohms, so maybe it just doesn't interfere with the current feedback. For regulation purposes, let's just wind this up to a little bit more output voltage. In fact, if I take this all the way up to 24 volts output or nearly 24 volts I don't actually know what the voltage is. Let's try again shorting those resistors.

and no, there just isn't any effect with a dead short across these current measuring resistors. So I might actually be okay having these power supplies in parallel, driving separate loads. But where those loads have a root back through the negative connection, effectively connecting these negative outputs together, which would make the current measuring in these resistors a mess really? Um, well. I Think that's all I can do at the moment.

Until I get another one of these power supplies, It does seem pretty good. It's synchronous, so it's efficient. There's very little heat loss on it, the heatsink really didn't even get warm. It's pretty good value at around ten dollars per piece, and it's got a good voltage range.

and if you can, run these at up to 20 amps yeah, I think it's pretty reasonable. Butt Converter: That's it for the moment. Cheerio.