I’ve had the DROK LTC1871 for over a year now. You’ve probably seen either it or one of the many variants on Amazon/eBay. Here’s my sloppy pic to help you identify it if you’re not sure:
So the product description gives some of the basics… 3.5-30v range, ~15ma power consumption, 6A/10A current capacity, and so on.
A few things I wondered before I bought it… things it didn’t tell me were:
- What happens around that 3.5v low end?
- What happens if the input voltage exceeds the output voltage you’ve set?
- If the output pulls more power than the input provides, what happens?
- Does it remember which of the 3 display settings have been chosen after it loses power?
- …a few other miscellaneous bits
A few times, I’ve grabbed the meter and power supply to figure out something specific I wanted to know. Figured it’s time to write something up here so I’ll have the info for the future (and it just might answer a question for someone else too!). So here we go:
Low voltage behavior (~3.5v claimed minimum)
During use (boosting wind turbine output at very low voltage), I noticed that when we went from NO_WIND -> GUST_OF_SOME_WIND -> NO_WIND , as the voltage started to climb from zero the display would flicker for a bit before coming on for a brief moment and then would go back off. Was it actually generating power during that “flicker” time?
A little time diagnosing and here were the answers:
- < 2.1 volts – power gets passed through the device, minus about 0.15v. So if you’re supplying 1 volt of power, about 0.85v will end up on the output end. No boosting and the DROK itself doesn’t really draw any current (quite a bit less than 1 mA). The device isn’t really “on” or anything.
- 2.1 volts – this is the point where the DROK “tries to work”. By that, I mean the input and output voltages will both bounce up and down as it presumably tries to pull enough power to activate the device (but can’t quite do it). It starts to draw current but this bounces up and down too. If you have something on the output, it’ll get intermittent bouts of power up to the set voltage, but not likely enough to do anything with except measure. This is also the point where it
- 2.36 volts – the output stops bouncing (consistent output at your set voltage, at no load).
- 2.5 volts – both the input and output stop bouncing (consistant voltages at no load). This is the point where you could probably say it’s actually working.
- 2.7 volts – the numeric LED powers on, but is dim and displays 0.
- 2.76 volts – the numeric LED displays the correct voltage.
- 3.77 volts – the numeric LED is at full brightness.
Summing this part up, the 2.5 volt mark is where I’d say the device actually starts working. Below that, on the output end you’ll either get the input voltage (minus 0.15v), or you’ll get bursts of the boosted voltage. Above that 2.5 volt mark, you’ll start to see the LED coming on.
High Voltage behavior
This one’s a bit shorter. Basically, if you’ve set the output to… say… 10 volts, and your input is higher (say… 15 volts), what happens?
The answer is that the voltage seems to be pretty much passed-through as is, with a 0.15v voltage drop. So in the above example where you set the output to 10 volts but were feeding the input 15 volts, you’d end up with about 14.85 volts actually coming out the input.
The LED shows the *actual* output coming out, so in the above example you’d see ~14.9 volts.
Comparing both input and output sides (reported by device vs my voltmeter), I’ll sum this up by saying “it’s close, but use a meter if being off by 0.1 volt will make or break you”.
Actually use a meter anyway when fine tuning… just because mine was within 0.1 volts doesn’t mean yours won’t be off by a couple volts.
Current draw of the DROK device
Nobody likes a power hungry device. DROK listed the power consumption as “around 15mA”. I measured at a few input voltages and here’s what I got:
- 1.1v – 0.1mA power draw (0.0001A).
- 2.6v – 5.5mA
- 3.7v – 11.7mA
- 7.6v – 10mA
- 16.5v – 9.9mA
Note that toying with the output voltage had a tendency to move the output +/- 1mA. The general trend seems to be ~10mA consumption though. Big exceptions are when the voltage is so low that the device is pretty much inactive (near 0), and when the device is at the stage where it’s “on but no LED” (around 5-6mA).
Connecting the DROK to a heavy load with a current-limited input
I wanted to see what happens if the output wants to draw more power than the input can supply. The handiest load I had around was a 12V car battery, which was sitting at around 12.1 volts. I severely limited the current on my bench power supply (and set it to about 6v to force the DROK to do some boosting) and did some testing:
- with the output set to 13.6v, the device “worked” but the display went out
- with the output set to 12.5v, the device “worked” but the display went out
- with the output set to 12.2v, the device “worked” but the display went out
…you can see a pattern.
By “worked”, I mean the output voltage measured at the battery terminals went up (from ~12.11 to around 12.19 in all cases). So the DROK was working. Display does go out though.
Knowing that the display will go off if your input doesn’t have enough oomph to power the output with some left over to power the display is something really handy to know.
Display Memory? Nope.
I really liked the feature where you can change it to show input voltage, output voltage, or rotate automatically between both.
Sadly, the device doesn’t have a memory. As soon as it loses power, it goes back to the default (showing output voltage). I suppose it’s not the end of the world, but still… if you’re planning to use it for something like solar or wind (which both drop to 0 at some point), and have it permanently mounted, it’s a bit of a bummer to have to hit the button if you want to see the input voltage.
Well, it’s been a year and the thing still works. It’s been repeatedly exposed to input voltages from 0-25v, been glued and then pried from a mounted panel, and has just kept on going.
On it’s own, I’d say it’s been a really solid little device. However, I also have a DROK 12-60V boost converter, bought at the same time, hooked up to the same equipment, which has failed rather catastrophically (internally shorts and creates >100v output at between 10.6-11.5v input).
So I wouldn’t say “DROK devices are all great”, but I would say “this particular DROK device has been really good”.
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