"48V" DC - DC converter cut-off voltage question

I'm planning to add a DC-DC converter to at least one if not both my TSDZ2 48v bikes so that I can add robust 12v lighting for night riding - including lighting for my trailer - and after spending hours looking at options, it looks like I've got really two options that financially make sense, but they have trade-offs and so I'd like the opinion of those of you with 48v systems. (I spent a lot of time looking here on ES for a good answer to this, but haven't found it so far, so please forgive if this is "asked and answered" and point me to it!)

The better one I like because: better packaging (ie how it would mount / looks, etc), a better (published) efficiency of 90%+, AND, shipping from the USA - I can have it by Monday if I order today. Only down side: published cut-off input voltage of 40V.

The second (and third and fourth, all share these characteristics) has only ONE possible advantage: a published cut-off voltage of 36V. The down sides are dorky looking packaging, non-published efficiency - which tells me it has to be low - AND delivery dates that are off into November / December!

I'd like to go with the first option but I'm concerned that I might loose my lighting if the pack ever drops below 40v. And here's where I have no experience! I have NEVER taken my pack below 50v (at rest), much less 40! However, I have read the specification sheet for my brand of 18650 cells and a "48V" pack (13S) should be "officially in need of a recharge" at 36.4v. ... Yes, I know it's REALLY bad to bring your pack down that low all the time for longevity reasons, but you never know what the future may hold, so... It'd be REALLY bad to lose lighting because the pack dipped below 40V (but wasn't yet to 36).

Another thing to consider I don't (yet) have any direct experience with but know to be concerned about: I know (from other experience) that the resting voltage of a battery and the in-service, during load voltage are two very different things! And since I don't have a meter on my system (yet), I have no idea what the pack voltage is actually like when I'm using it full bore when its at-rest voltage is, say 50. BUT, my system is only rated at 18A, and other users of the TSDZ2 say the actual usage is very modest. So MAYBE the difference between rest voltage and full load voltage isn't so great - but it's an unknown to me at this time.

Please share your insights!

Order in the next 1.5hrs and you can have by Friday.

https://www.amazon.com/DROK-Numerical-Converter-Regulator-Stabilizer/dp/B01MSJQAKY/ref=sr_1_3?ie=UTF8&qid=1507754228&sr=8-3&keywords=60v+dc+converter

I like flat tires suggestion. Might get one for myself. I did read in the reviews that earlier versions did not remember the outputs settings when power was removed, but that later units do.

Also wanted to comment that while 18650's are rated for AH using discharge down to 2.5V per cell, no one really runs them that low. The motor controller usually shuts off around 3V/cell (~40V) for a 48V battery. The Battery BMS is also often set for similar levels.

flat tire said:

Order in the next 1.5hrs and you can have by Friday.

https://www.amazon.com/DROK-Numerical-Converter-Regulator-Stabilizer/dp/B01MSJQAKY/ref=sr_1_3?ie=UTF8&qid=1507754228&sr=8-3&keywords=60v+dc+converter

Click to expand...

OK, that "answers the question" a different way - by side-stepping it. But this one has NO packaging and, it's rated for indoor use, 80% humidity... I'm going to use it in rain... Plus, I read the reviews. People said: (these are quotes)

* Burned out after two months of light use
* Noisy switched output cannot directly drive microcontrollers (but can power anything that has its own regulator)
* if only it saved your last settings [...] it always seems to default to 5.0V 3.0A

For me, having to reset it every time would be too much of a pain in the ass. And, I don't really want to make the packaging myself unless I get a MUCH better unit - like maybe if I could package THIS myself easily: https://www.digikey.com/product-detail/en/vicor-corporation/PI3546-00-LGIZ/1102-5475-ND/5321312 . They do sell an "evaluation board" for it that maybe could be a good start...

While I appreciate the suggestion, I'm still looking for battery voltage insights - OR a different option that's

docw009 said:

Also wanted to comment that while 18650's are rated for AH using discharge down to 2.5V per cell, no one really runs them that low. The motor controller usually shuts off around 3V/cell (~40V) for a 48V battery. The Battery BMS is also often set for similar levels.

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So, you're saying the 40V cutoff may be a practical choice? That's good news... Can anyone else support that? Any "me too"s?

If so, here's the one I'll probably buy:

http://www.ebay.com/itm/New-DC-GOLF-CART-voltage-reducer-converter-48V-to-12V-10A-120W-Power-Supply-/282381261696?hash=item41bf3c1b80:g:Gh4AAOSw-ZBZpL5E

Yes, you would be really stupid to run your batteries down to 3v a cell. Don't do that. Leave at least 20% left in the tank and they will last a lot longer and not go out of balance.

I'm running this one:
https://www.amazon.com/gp/product/B0151BF6DI/ref=oh_aui_detailpage_o07_s01?ie=UTF8&psc=1

6-60 volt input. 60watts. Waterproof and shock resistant.

wturber said:

I'm running this one:
https://www.amazon.com/gp/product/B0151BF6DI/ref=oh_aui_detailpage_o07_s01?ie=UTF8&psc=1

6-60 volt input. 60watts. Waterproof and shock resistant.

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Thank you, wturber, that's a possibly better unit than I was thinking of for TWO reasons:

1) Will get me home with lights, even if I'm pedaling all on my own, no matter how far I've drawn down the battery. And;

2) Probably has better efficiency with a published 94% - and in my book, that matters.

Aside from that it's a little more expensive, the only potential downside is that it has only 5A instead of 10A. ... I PROBABLY don't need more than 5A, but now I'm going to have to go count up the amps whereas before I was sure it was more than enough!

Any other good choices to consider?

RTIII said:

wturber said:

I'm running this one:
https://www.amazon.com/gp/product/B0151BF6DI/ref=oh_aui_detailpage_o07_s01?ie=UTF8&psc=1

6-60 volt input. 60watts. Waterproof and shock resistant.

Click to expand...

Thank you, wturber, that's a possibly better unit than I was thinking of for TWO reasons:

1) Will get me home with lights, even if I'm pedaling all on my own, no matter how far I've drawn down the battery. And;

2) Probably has better efficiency with a published 94% - and in my book, that matters.

Aside from that it's a little more expensive, the only potential downside is that it has only 5A instead of 10A. ... I PROBABLY don't need more than 5A, but now I'm going to have to go count up the amps whereas before I was sure it was more than enough!

Any other good choices to consider?

Click to expand...

FWIW, I used that converter along with a 10W and 20W halogen light and my bike LCD and LED taillights to pull 35watts to test the capacity of one of my 36v modules. It took over four hours to drain down that one 36V 4.3ah pack. I run LEDs on my bike and pull less than 10 watts. If you use LEDs, 60W should be overkill.

But if you need more power, try this one. It is bigger and weighs more.
https://www.amazon.com/dp/B0756T983Q?psc=1

12V at 5A is 60 watts. That's alot of LED.

dustNbone said:

12V at 5A is 60 watts. That's alot of LED.

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Yep. My 50 watt equivalent LED (probably an exaggeration) lights up the road well enough for me to ride at 20+mph on unlit streets at night. Combined with my rear LED strips, my lights pull less than 10W. I could add five more headlights like the one I have and still not run out of 12v power.

RTIII said:

wturber said:

2) Probably has better efficiency with a published 94% - and in my book, that matters.

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Depends entirely what voltage range you run it in. It could be a lot less efficient than that at your pack voltage, but with the small power draw of LEDs it shouldn't matter.

flat tire said:

RTIII said:

wturber said:

2) Probably has better efficiency with a published 94% - and in my book, that matters.

Click to expand...

Click to expand...

Depends entirely what voltage range you run it in. It could be a lot less efficient than that at your pack voltage, but with the small power draw of LEDs it shouldn't matter.

Click to expand...

Not my quote.

But based on the rated loads and the measured draw when I did my capacity test, with a 36v pack and a 30+ watt draw, the converter appears to be efficient enough that loss is hard to notice. With my lighting system the loss is too small to matter at any practical level.