Cheezeball DC Load: DL24P: Pump, or Dump ???

[Pukker]

I am intending to use my dl24 not more than 100w, but not wanting to blow mosfets. After reading full 15 pages I did not get clear solutions. NOW, what should i do to not burn mosfet?
1. should i use 15v 1 zener or 2 zeners back to back?
2. or use 5.1v 1 zener or 2 zener back to back?
3.or use tvs diode of what ratings?
4. should i remove c5?
6.should i have to reinforce diode, tracks, cooler for 100w?
7. can i use regular mosfet than linear?

I use the DL24 for lot of testing en logging.
I agree, max. 100Watt is safe to use it without fear.
Replaced the fake mosfet with an original IRPF260 and placed an zener.
Glued an small heatsink on the protection diode and placed an good tower cooler.
When using the load with max. 100 Watt and max. 6 Ampere (diode is heating up),  it is reliable and safe.
When you like to be safe, i.e, start testing and leave it running without risk,
these max. ratings should be respected I believe.
Electronics aren't happy with extreme stress.
Chinese specifications are chinese specifications, keep that in mind.
With TestController the unit is very useful and its accuracy is pretty good.

When you want to disipate more power, you should reinforce tracks, diode and so on.

https://www.eevblog.com/forum/testgear/program-that-can-log-from-many-multimeters/

[MrPete]

Simple question for those with DL24MP -- does it support a *wired* PC connection, or only BlueTooth? (I'm guessing USB if anything...)

[ruahriman]

Only bluetooth. If You will connect it via wire, you will blow up your USB ports, MCU in head module of load and something else

[MrPete]

A set of real world application questions similar to SA's... this time applied to DL24MP which has 4 MOSFET's:

1) Is this device safe to use in any way without modification? (I get the sense there's danger with at least some DL24xx models due to Vgs excursions way past the usable range.)
2) My application is battery (Prius NiMH module) testing, max ~8.5V @ 6.5 A = ~55 W ... should that be well within the safe zone?

Thanks heaps..

[thm_w]

A set of real world application questions similar to SA's... this time applied to DL24MP which has 4 MOSFET's:

1) Is this device safe to use in any way without modification? (I get the sense there's danger with at least some DL24xx models due to Vgs excursions way past the usable range.)
2) My application is battery (Prius NiMH module) testing, max ~8.5V @ 6.5 A = ~55 W ... should that be well within the safe zone?

Thanks heaps..

These newer models shouldn't have gate issues as far as I've seen, and the FETs on mine are rated to 30V Vgs. You can read frogblenders post on the previous page.
The main issue is if the FET you get isn't appropriately rated, and you run it above ~100W, it may fail.

I would say its good choice for that sort of battery testing. Though if you are testing a large battery I would consider adding a ~20A automotive fuse in series just in case the FETs do short out.

[Pukker]

When working with heavy batteries, wich can produce extreme high currents when shorted,
(they can even explode) using a fuse is the first thing to do.
I like the DL24 loads when talking about price, working, accuracy etc.,
but safety is not first priority at Atorch.

Especially when doing Battery-Capacity tests, over a long time,
and you can't keep it in sight constantly, safety is needed.

[22euu]

Some people here mentioned using MOSFETs designed for linear operation. Reading up on the subject a bit more if you derate the power by a factor of 3 or so, you can safely use standard MOSFETs. I've used standard MOSFETs for the electronic loads I've designed. Then again, I've never come anywhere near their rated power in operation. If you're aiming for 150 watts on the DL24 with a standard MOSFET, then buy one rated for at least 450 watts. The primary advantage of using standard MOSFETs is they're much less expensive. Since I had a parts order from Mouser for another project, I also bought a pair of IRFP90N20DPBF. Power rating is 580W. I can probably safely run these up to maybe 200W. A comparable linear MOSFET ( IXTH60N20L2 ) costs about 3 times as much, although I would be able to safely go to its full power rating of 540W.

I might buy a few of the DIY devices to test/modify. They're certainly cheap enough. The parts alone would cost me more than the ~$20 they sell for.

Hi @jtr1962

I intend to modify the DL24, but before to order the necessary parts I need your advice on what I want to do, considering that the price of the components is higher than the price for the DL24

The electronic load will be used below 50V, 40A max, within the limit of 500W max.

1. Which is the most suitable Mosfet to replace the original: IXTH140N075L2, IXTH110N10L2 or IXTH60N20L2?
2. The diode for reverse protection will be replaced with VS-100BGQ100.
3. The original shunts will be replaced with 2 x WSHP2818R0100FEA.
4. Does the 15V zener diode for eliminating spikes matter how it is mounted - Anode to Gate and Cathode to Source, or vice versa?
5. Also, the copper tracks on the board will be reinforced and the cooling of the mosfet will be changed.

Please advice,

[JimnyVR5]

My DL24P arrives tomorrow

You guys think I could reduce the blowing-up by connecting the load after pressing on (after the overshoot happens)?

Edit: If I just power the thing with the minimum 8VDC - does that give me some extra protection?

[...]

After much reading, I believe the whole "exploding fets / zener diode" problem is not exceeding the fet's ±30V Vgs spec...

...the problem is the dumb firmware going to max (11v) for 100ms when you press the ON button (see overshoot picture below:  it is from the excellent work done by @deuteron ).   11v is fully ON for most fets, and then you have near-infinite current.... which is far beyond the SOA.

[...]

[Moduvator]

Recently came across one of those units on sale so I thought I would grab one. The version I got had DL24E-a on the silkscreen and shares the familiar 4-FET configuration with transistors marked as IRFP264.

Having read about the gate control voltage horrors, I decided to probe mine. I am using my cheapy $20 pocket oscilloscope, so the readings I got are to be taken with a grain of salt, but I find that it tends to perform OK at the time bases we are dealing with here.

So first of all, there does appear to be a slight ramp up time when the load is switched on as the gate control voltage softly rises over 4-5 ms. No glitches, no ringing, the current rises and just stays there, so they at least appear to have addressed this issue?

Rather predictably though, if I start current limiting my 150W 30V power supply I was testing this unit with, the whole system would start oscillating wildly with gate voltages jumping as high as 12V before the cycle would repeat again. Curiously enough, after a few seconds of jumping like this, the load appears to give up and disable itself, even though the display still showing ON. It's worth noting that 12V is the actual supply voltage from the dinky power adapter they include so it would appear to be the maximum they drive the MOSFETs with.

Another surprise came when I was selecting different modes with the load off and still connected to the power supply. I heard clicking noises from my PSU which it usually makes when there are sudden current spikes and sure enough: even when the load is off, changing the modes causes a glitch on the gate, opening the transistor fully for a few milliseconds before reining it back in. Sometimes those glitches are just a couple spikes, lasting less than a millisecond, but still a lesson learned: best to disconnect the load completely when changing modes!

[Gridstop]

It looks like the new DL24E series has that 4 pin TTL level serial port for a cabled connection which I would prefer. I know the DL24M series has bluetooth and shows up as a bluetooth serial port, but does anybody know if it's a separate bluetooth module so one could patch in a TTL serial cable instead?

It doesn't look like there's anything on the main power board so I'm assuming it would be inside the display panel on the DL24MP, maybe most people haven't opened that.

[Moduvator]

I have been experimenting some more with my load and made a few more interesting discoveries.
First of all, the load actually had no issues running continuously at 130W with FETs temperature settling at about 85°C so I imagine with a beefier heatsink and/or a stronger fan the rated 150W actually look quite feasible. That being said, I wasn't able to actually test that as it has been quite successful at killing my "150W" Chinesium lab power supply at least twice when trying that. After I mended it for the second time I've discovered I can only reliably get about 130W out of it since at full bore it goes into a thermal runaway, unable to sustain 30V at 5A, which is how I appear to have killed it previously.

Another interesting discovery has been quite an alarming and has to do with remote voltage sensing. There are separate binding posts for that on the load proper, however it turns out that the positive of that is connected to the other side of the main fuse via a 30k resistor. This means that if you are using remote sensing and there is a failure and the fuse blows, the load will still attempt to sink the current, now using the sense line, until that resistor emits the magic smoke (ask me how I know).
Now, I don't have much experience on how an electronic load should be constructed but something tells me that's not how you plan for a failure mode. Definitely something to watch out for!

[odemontealto]

DL24 is a serial killer of mosfets. If you buy it, the next thing is to start wasting money buying mosfets