Power Bank as Emergency Booster Battery? / Bath Mat for the Mental Fool

[Catalyzt]

Translation: Basic Math for Elementary School - Strategically Erase Letters on Cover of Math Book = Bath Mat for the Mental Fool

I have a 7Ah 48 volt battery (which I figure at 336 Wh) that is absolutely fine for most of my needs. I can probably get 30 miles out of it given moderate to severe hills and plenty of effort, probably a bit more if I charged it to 100%.

What I am wondering is if I could use a small power bank as an insurance policy if I want to do some longer rides, and I'm betting that someone here was crazy enough to try this and tell me what a good/bad idea it is so that I don't blow anything up or get stranded.

Larger power banks are very heavy, and I probably would only come up 5 to 12 miles short. Could I just throw my charger and a 167 Wh power bank (or even smaller) into a backpack, pull over under a tree somewhere with a book when I hit the battery reserve, sit there for an hour or so, and power up enough to get home?

It's sort of a stupid idea. The power bank weighs four pounds and the charger probably a pound, so I'd be riding a 47 pound bike instead of a 42 pound bike, at which point I might be better off just riding my other eMTB, which actually weights 47 pounds and has a 428 Wh battery.

Or, is there some other way to make this a less stupid idea? Feel free to say things like, "Oh, yeah, sure, I tried this with a KrazyCharge 120 Wh power bank, which is only 2.5 pounds, but gave me an extra 10 miles of range, you don't even have to get off the bike" or "OMG, are you crazy?! You'll over-drain the battery bank, and start a symbiotic chain reaction which could open a black hole to a parallel universe where no organic life ever evolved!"

Thanks. I could have just asked Pedaluma, but I thought it would be more fun to see what crackpot solutions other weirdos here have already tried, and how it worked out.

 

[mschwett]

mmmm. you're going from AC, to DC (to charge the power bank) and then from DC to AC to plug the e-bike charger in, which then goes from AC to DC to charge the e-bike battery. not sure how much power you'd really get but it's not going to be 167 Wh. if all the charging electronics were in the bike and it had a DC input, you could possibly use a USB-C PD output from a power bank and skip power losses and extra weight. i don't think many/any bikes are like that though.

the output specs on the AC for most power banks that size are about 100w, which may not be enough for your charger. a lot of the mainstream bikes have chargers in the 4A range, which is more like 160w before all the power losses. so i'm guessing it's not going to work particularly well unless your bike's charger is tolerant of low input power.

 

[Jeremy McCreary]

Feel free to say things like ... "OMG, are you crazy?! You'll over-drain the battery bank, and start a symbiotic chain reaction which could open a black hole to a parallel universe where no organic life ever evolved!"

The black hole thing happened to me once. Not much to eat. I wouldn't risk it.
;^}

This is actually an interesting question. Hope you get a knowledgeable answer.

 

[Catalyzt]

mmmm. you're going from AC, to DC (to charge the power bank) and then from DC to AC to plug the e-bike charger in, which then goes from AC to DC to charge the e-bike battery. not sure how much power you'd really get but it's not going to be 167 Wh. if all the charging electronics were in the bike and it had a DC input, you could possibly use a USB-C PD output from a power bank and skip power losses and extra weight. i don't think many/any bikes are like that though.

the output specs on the AC for most power banks that size are about 100w, which may not be enough for your charger. a lot of the mainstream bikes have chargers in the 4A range, which is more like 160w before all the power losses. so i'm guessing it's not going to work particularly well unless your bike's charger is tolerant of low input power.

Interesting, thanks for this. I did understand most of the this, though I'm not sure it matters about the power going from AC to DC; the battery for the power bank is rated by how much charge it can hold. Once the battery is charged, how would the inefficiencies of charging it factor into the equation? (Other than the fact that you're spending a few dimes or dollars more on electricity.)

As for the specs of the power bank I'm looking at, those would be:

<< Lithium backup battery pack is equipped with 167Wh capacity(45,000mAh), 2*USB ports(5V/3A,9V/2A,12V/1.5A QC18W), 1*USB C port(5V/3A,9V/2A,12V/1.5A PD18W), 2*AC ports(110V/60Hz, 100W, peak 200W), 2*DC ports(12-16.8V/10A, Total 150W MAX). >>

It sounds like this this thing could put out 160 W and still not be at peak, do I have that right? And the DC ports are no help, correct-- like, don't even think about it, if for no other reason b/c I can't get juice outta the powerbank and "directly" into the controller or motor or whatever.

Or maybe I SHOULD think about it. Maybe the battery could take DC in straight from the DC out on the power bank... @Jeremy McCreary , yeah, I think that would open the black hole. Or maybe it's a wormhole, or just a more generic transdimensional portal. Like the one that opened in the wall of our old apartment in New York and that my ex-roommate tried to dive through in 1984 or so. (We did tackle him so he didn't get a concussion, or we stopped him from making a great leap forward for mankind, depending on whose version of the story you believe.)

One AC outlet is three prong, the other is two prong. I will check the specs for the charger... if they are listed and I can figure them out. My father was an engineer, you'd think I'd have a better brain for this kind of thing... though weirdly, despite the lost brain cells of my dissipated youth, it's easier to think about and makes a bit more sense than it did 15 years ago, when thinking about anything electrical was actually painful.

 

[mschwett]

not sure what they mean by “100w, peak 200w” on the AC ports. take a look at your e-bike charger and see what the input current is. they usually say and from that you’ll see how many watts it needs.

my point about the repeated transforming is that the power bank has 167wh stored in a DC battery, it’s going to convert it to AC (some energy is lost) and then your bike’s charger is going to convert it back to DC, more energy lost. i don’t think DC to AC is better than 85%, the AC to DC is probably around 90% so you’re talking about 90% of 85%, or around 76-77%. you’re going to add more like 128wh to your bike, just as a guess, IF the nominal 100w is sufficient. specialized’s full size charger, as an exanple, outputs 168w, and shows a max input current of 2.5a at 100v (250w) but presumably much closer to around 185w. plug your charger into the power bank at home, see if it charges your bike!

risk of black hole is statistically very low.

 

[6zfshdb]

Why not spend the money on a cordless tool battery instead of a power bank? You could use one of these to convert to AC for your charger. A tool battery will provide enough current without overloading anything.

Amazon.com

Or, a more efficient way would be to use one of these, and direct wire the DC tool battery to the bike:

Amazon.com

I use DeWalt batteries for my tools, so I always have them around. Similar adapters are available for other battery brands as well.

This way, you don't have to wait for the charger to charge the bike battery, or even carry the charger at all..

In my case, I get around 19 miles from a 4AH, 60V tool battery.

 

[indianajo]

Yes, the cordless 40 v ryobi 6 AH batteries have about 240 AH and would energize a 36-48 v capable controller. Once the controller forgot about the 48 v 17.5 AH battery I ran down on the 80th hill. I bought one of those ryobi battery to wire converters last December and it arrived at 10AM the day I left for the airport at 6AM to go to my brother's. The apartment dweller that stole it out of the mailbox probably had a lot of fun trying to sell his find.
I have 3 of the ryobi batteries as I cannot complete my yard with 2 unless I wait a couple of hours for one of them to recharge. They are too hot to charge right after I pull a dead one out of the mower battery compartment.
As far as another 17.5 AH 48 v battery, it would fit in the pannier but my hips could not stand 60 miles in a day. They really hurt after 30 miles, which the main installed battery will power okay. There are a couple of late summer+fall concerts that are about 40 miles from my summer camp, but I haven't had the nerve to ride to one yet. Something about the spare battery being loose in the pannier while I am on the concert grounds. I have lost $50 in tools while the bike was parked & locked up, a couple of lights have been cut off, two tires were stabbed, so lowlifes do paw through my possessions occasionally. Nobody has had the ****s to attempt to cut the 3/8" SS sling that locks the bike to the power pole or gas meter.

 

[harryS]

Well, if you already have a powerbank with an AC outlet, go knock yourself out. as the daughter-in-law and now my grandkid like to say,

Here's my version of a powerbank. You got an ebike battery on the left, powering a 48V-12V golf cart converter in the middle. On the right is a 12V-110VAC inverter. On the bottom is an ebike charger plugged into the inverter,

The charger puts out 2.5A at 48V. In this subsequent picture, I put a wattmeter after the battery. I found it measures 3.3 amps out of the battery at 50V.

To a rough approximation then, the efficiency is 25/33 or 75%, better than I expected. Perhaps an active EE can find something in my experiment that I forgot. I'm just a retired one.

 

[mschwett]

... the efficiency is 25/33 or 75%, better than I expected. Perhaps an active EE can find something in my experiment that I forgot. I'm just a retired one.

cool experiment. and essentially exactly the efficiency that i predicted based on the most common transformers out there!

 

[Catalyzt]

Why not spend the money on a cordless tool battery instead of a power bank? You could use one of these to convert to AC for your charger. A tool battery will provide enough current without overloading anything.

View attachment 178507

Amazon.com

Or, a more efficient way would be to use one of these, and direct wire the DC tool battery to the bike:

View attachment 178508

Amazon.com

I use DeWalt batteries for my tools, so I always have them around. Similar adapters are available for other battery brands as well.

This way, you don't have to wait for the charger to charge the bike battery, or even carry the charger at all..

In my case, I get around 19 miles from a 4AH, 60V tool battery.

Direct wiring the DC tool battery to the bike sounds like the best way to go-- I love saving weight, love it, love it!

But to make it safe, I think I'd want to solder a the appropriate female cable adapter to the cables and rig some kind of harness for the tool battery and adapter. The move, I guess, would be to unlock the primary battery when it was dead, throw it into a small backpack, and then strap the tool battery/adapter somewhere secure before plugging it in to give me juice for those last few miles home. Great stuff, guys! NOW it's time to bring in @PedalUma, and see if he thinks it's possible to rig this kind of cable adapter for the TSDZ2.

I should probably also ask him if the tool battery could power a small set of ornithopter wings-- just enough to manage a 500 foot flight at two or three feet off the ground. But I don't want to hijack my own thread. And yes, I am capable of doing that.

 

[PedalUma]

Just don't fly too close to the sun. As long as I had 36V or 48V sure. But right now I am working over 50 hours per week at a bike shop. I mentioned in another thread that my right hand is now thick with meat from all that wrenching and it is three mechanics with no sales people, yet we sold 64 eBikes for June.

 

[PCeBiker]

Translation: Basic Math for Elementary School - Strategically Erase Letters on Cover of Math Book = Bath Mat for the Mental Fool

That reminds of this from Mad Magazine in the 70's,..

wEight wATchERS

I remember a Christmas Carol too,..

We three clods of Omaha are
Spending Christmas eve in a car
Driving drinking glasses clinking
Who needs a lousy bar

Drink to Melvin drink to Fred
Drink to those two trucks ahead
Swerving speeding signs unheeding
Drink till they pronounce us dead

 

[PCeBiker]

Why not spend the money on a cordless tool battery instead of a power bank?

Thanks for your post !!!

I've been struggling to make a connector to plug my tool batteries into.
I thought I had to sacrifice a tool to scavenge the socket from it.

I just found these on Amazon,..

I need an adapter for my new mower.

 

[6zfshdb]

Thanks for your post !!!

I've been struggling to make a connector to plug my tool batteries into.
I thought I had to sacrifice a tool to scavenge the socket from it.

I just found these on Amazon,..

View attachment 178533



I need an adapter for my new mower.


View attachment 178538

A word of caution when using cordless tool batteries. With some brands, the low voltage cutoff (LVC) is located in the tool, not the battery. When using a battery without an LVC in a bike, it is possible to over discharge it, causing damage.

If your bike's controller has an LVC, make sure the setting is at, or above the minimum discharge voltage of the battery you're using.

LVC circuit boards are cheap and can be wired as insurance, but I just use a gauge to monitor the voltage.

 

[6zfshdb]

Direct wiring the DC tool battery to the bike sounds like the best way to go-- I love saving weight, love it, love it!

But to make it safe, I think I'd want to solder a the appropriate female cable adapter to the cables and rig some kind of harness for the tool battery and adapter. The move, I guess, would be to unlock the primary battery when it was dead, throw it into a small backpack, and then strap the tool battery/adapter somewhere secure before plugging it in to give me juice for those last few miles home. Great stuff, guys! NOW it's time to bring in @PedalUma, and see if he thinks it's possible to rig this kind of cable adapter for the TSDZ2.

Many of my bikes use Anderson connectors so I made up a jumper cable to use the tool battery. Something similar can be done with almost any connector. The parts fit neatly in a canvas tool bag for a bit of protection. The whole kit weighs less than 3 pounds.

Tool batteries are built for rough handling so I'm not worried about damage. I just throw it in my rear rack bag, pannier or hang it on the frame somewhere on rides where I think I may need it:

 

[6zfshdb]

Thanks for your post !!!

I've been struggling to make a connector to plug my tool batteries into.
I thought I had to sacrifice a tool to scavenge the socket from it.

I just found these on Amazon,..

View attachment 178533



I need an adapter for my new mower.


View attachment 178538

Just get one of these bikes and a conversion kit:

That way, it's self propelled!

 

[PCeBiker]

I was thinking of getting this riding mower,..

And use it to tow a more powerful 40 volt push mower (well,.. pull it.)

This one comes with two batteries that may be used in series to get more power,..

This one has four batteries and is self propelled,..

The riding mower comes with a remote control so I can mow the grass while sitting comfortably in my chair driving remotely,..

But it doesn't appear to steer the tractor, so I'd need to hire a toddler to drive it.


I found this remote control dolly, but it's a little out of my price range,..

I need a remote control toy tow truck that goes slow and can tow ~ 40 pounds.

 

[PCeBiker]

A word of caution when using cordless tool batteries. With some brands, the low voltage cutoff (LVC) is located in the tool, not the battery. When using a battery without an LVC in a bike, it is possible to over discharge it, causing damage.

I'm pretty sure that Ryobi has it in the battery, but I'm gunna probe it with my voltmeter before and after the battery shuts down to verify that.

 

[PCeBiker]

What have you got here??

Does that battery flip between series and parallel to provide two different voltages ??

 

[6zfshdb]

What have you got here??

View attachment 178561


Does that battery flip between series and parallel to provide two different voltages ??

Yes, it's one of the DeWalt Flex Volt batteries that will switch between 20V and 60V. The 9AH rating applies to the 20V configuration. It's just 3AH at 60V.

There is a newer 15AH version which will supply 5AH at 60V.

Amazon.com

Quite pricey but It does dual duty with my collection of DeWalt tools though.