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I recently purchased a step-up converter, the specifications state that it can boost 5 V to 30 V with varying input voltages.

The reason I purchased it was because the charger for my handheld vacuum cleaner stopped working, and the charger has very specific specifications that are hard to replace: 27 VDC 85 mA.

I'm currently using 12 VDC 1000 mA as an input and stepping it up to 27 V, my question is is this safe, and will it work correctly?

TLDR: I have a step-up voltage converter/regulator that works within 5-30 V, I have a 12 VDC 1000 mA power supply that I want to step-up (boost) to 27 VDC 85 mA and I'm wondering if it will work correctly.

PS: I have a higher current 12 VDC power supplies at 2000 mA, and one have a 19 VDC 2000 mA also. Would they be better to use instead?

PS2: This is the one I purchased: https://www.amazon.de/gp/product/B075SXMXN9/ref=oh_aui_detailpage_o01_s00?ie=UTF8&psc=1

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  • \$\begingroup\$ It all rests on your interpretation of what the charger that failed provides to the load. "27V DC 85mA" is pretty meaningless so why not post a picture of where you got this information instead of you interpreting it. \$\endgroup\$
    – Andy aka
    Oct 27, 2018 at 16:27
  • \$\begingroup\$ Heya Andy, thanks for the reply, the charger that failed is the charger that was provided with the device that i'm trying to get working again. Here is the picture that you requested i.imgur.com/HI9D5tZ.jpg \$\endgroup\$
    – DarkCloud
    Oct 27, 2018 at 16:33
  • \$\begingroup\$ It's possible that the 85 mA rating is a constant current that charges the vacuum cleaner's battery and that in doing so it won't produce a terminal voltage greater than 27 volts DC. OR it produces a terminal voltage of 27 VDC and has a current limit of 85 mA. Either way, it is a guess as to what they mean. \$\endgroup\$
    – Andy aka
    Oct 27, 2018 at 16:48

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Will it work correctly?

Maybe. There's three parts to your question.

  1. Will the approach work? -- Maybe, maybe not. There's a possibility that they designed that wall-wart to feed straight into the battery pack with no other management. This scheme would work if the thing has NiCd or lead-acid batteries.
  2. Are the parts you've selected of sufficient quality? -- Maybe, maybe not. I'm going to put aside my prejudices against no-name boost converters bought off the Internet for this one.
  3. Assuming that the answers to 1 and 2 are "yes", here goes:

The way you do these calculations with switching regulators (like your step-up converter) is to remember that power out = power in - losses. It's safe to assume that even a crappy no-name eBay special converter will be 80% efficient (although there's always surprises out there). If you do the math, this works out to power in = power out / efficiency.

So, you need 27V @ 85mA, which works out to something a bit over 2W, certainly less than 2.5 (I'm doing the arithmetic in my head -- feel free to check my work). You have a power brick that'll do 12V @ 1000mA, or 12W. Even given my in-the-head calculations, you're fine.

Is it safe?

Probably -- see my prejudices against no-name Internet purchases. There's a slight possibility (especially if the thing's got a really lame charging system that just goes straight from the wall-wart to the batteries) that you'll toast the batteries. However, this would Simply Not Be Done with LiPo cells, and NiCd, NiMH or lead-acid cells won't burst into flame -- they'll just quietly die.

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  • \$\begingroup\$ Thinking about your situation as I wrote my answer -- are you sure it's the charger, and not that the batteries in the vacuum have crapped out? One of the downsides to the ease of charging NiCd and lead-acid is that manufacturers of consumer goods tend to stop trying as soon as they have a system that'll work over a dozen charge cycles without burning anyone's house down. A well-designed battery management system for NiCd or lead-acid cells should keep them going forever -- but you don't find those systems in consumer goods! \$\endgroup\$
    – TimWescott
    Oct 27, 2018 at 16:50
  • \$\begingroup\$ Thank you so much for your well written reply. Answering your question regarding the battery; i assume the charger is faulty because i had to replace it once before because of the same problem (but now they don't have any chargers because the model has been discontinued). Here is the exact model, amazon.com/BLACK-DECKER-BDH9600CHV-Dustbuster-Cordless/dp/… Looking at the reviews really makes me just want to get a different one now. But i have already invested time into this. If it breaks again i'm never getting one again from the same manufacturer. \$\endgroup\$
    – DarkCloud
    Oct 27, 2018 at 17:02

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