Best chemistry for mobile charging

[veloman]

I thought lipo would be the best route to go for lightweight ebiking. But since I want the option to charge at places I go, after factoring the cost of a decent power output charger, power supply, weight, and complexity, it doesn't seem to be all that great. I could get a tiny 50w charger, which wouldn't weigh much and be cheap, but what's the point? At 50w it will take hours to get any meaningful recharge. The weight of a 250w+ charging system for lipo will be over 4lbs itself, and >$160.

I want to be able to carry my charger. It almost makes SLA comparable, when you consider how easy and cheap it is to carry those tiny chargers.

Is there a better way? I still have these Konion V cells that no one wants to buy.... maybe it's worth it to build my own battery. No balancing and the simple small charger would be no hassle.

What about Thundersky? That seems a bit more turnkey, although at 20ah, it's best suited for really long trips where you want to carry that much battery.

I plan on eventually carrying solar panels to charge where I stop (beach, park, etc).

Could I use lipo, but only balance charge when I'm home? Mayble I could get a tenergy lithuim charger, then when I'm topped off away from home, plug in balancers for a few minutes, then I'm ready to go?

 

[amberwolf]

If you are not running the pack down far enough to come unbalanced before you do the remote recharging, then you can easily keep just topping it off as long as you have something that detects the HVC at cell level to prevent the fullest cell from going over the top.

Over time it will eventually unbalance the pack, but if you are not charging it up to absolute max, and not discharging it to minimum, it'll probably take a long time to get very unbalanced. Say, only 90%-95% charged, down to 60-70% discharged. That would probably be safe enough, and not do much unbalancing assuming the cells are close in capacity to start with.

So as long as the cell-level HVC tells the charger to stop early, once the first cell hits that point, you wouldn't have to worry about it. (normally when balancing the HVC would wait for the *last* cell to reach that point, as the rest would be shunting current thru the balancers, and the HVC would be higher, too).

Since you would probably want the HVC to hit early by some percentage when remote charging, you may want to use two different HVC modules for the pack--one that is part of your home charger, and one that is part of your remote charger, each one plugging into the cell-level connection for balancing (even though the remote charger wont' be balancing it still needs cell access).

Without all the extra stuff needed for balancing, just an HVC board ought to be lighter and smaller.

The charger may still be the same size, though, if it has to deliver the same amount of total power.

I don't know how long the actual balancing would take once you needed to do it, as that depends on your charger and balancer and BMS and stuff.

 

[dogman dan]

I've found the ping 5 amp charger to be the best opportunity charger I've had. At 48v, it will top off 5 ah in an hour. About 250 watts. No reason it wouldn't work, it would shut down at 60v, while 15s lipo would be only charged to 4v at that point. If you went with one of the many lifepo4 chargers that stop at 58v, you could do 14s lipo with it and charge to 4.14v per cell. What's not to love there?

And you could of course, always charge lifepo4 with it too.

And using some of the stuff others have been getting to use their meanwells, I'd think you coulld just build your lipo setup with a hvc, and then run the charger as the power supply. In case I'm getting confusing here, what I mean is you are bulk charging just like the guys using meanwells, but just using a lifepo4 charger as the power supply. It would be slower than a meanwell though. But with a shut off built into it, perhaps more convenient to monitor?

To me it sounds safe to just use the lifepo4 charger, the lifepo4 charger would be undercharging the lipo. But you'd need to monitor the charge and be there to turn it off when it's time. I wish there was an equivilant in a lipo charger. 48v, 300 watts, plugs into a wall socket. And under $100.

 

[jag]

I thought lipo would be the best route to go for lightweight ebiking. But since I want the option to charge at places I go, after factoring the cost of a decent power output charger, power supply, weight, and complexity, it doesn't seem to be all that great. I could get a tiny 50w charger, which wouldn't weigh much and be cheap, but what's the point? At 50w it will take hours to get any meaningful recharge. The weight of a 250w+ charging system for lipo will be over 4lbs itself, and >$160.

For mobile charging I would think a built in BMS for balancing is better (unless you are confident cells don't you out of balance)

Then a high amp charger. A Meanwell S350 weighs 1kg, supplies 350Wh per hour of charging and costs $40-50 on ebay. Sacrificing charger life you might try to run it a bit higher (500W?). Anyone has found chargers that do more that 300-500W per kilogram of charger weight?

 

[liveforphysics]

You could have a 1kw charger that fits in your pocket.

 

[heathyoung]

Cooling it would be a problem though

Waterproof and a bucket?

In all seriousness, an unisolated buck supply could do it, but the output voltage could be very dangerous if not handled carefully. I posted some suggestions for the insane not so long ago on component selection.

 

[liveforphysics]

As far as the battery choice itself goes, HobbyKing Nanotech cells are the absolute best option if you're looking to flash charge a small pack. They can be charged from empty to full in about 6-8minutes and stay cool while doing it.

 

[veloman]

That's cool to know if I wanted to spend the money, I could charge that fast.

But if I want to keep costs down, is there anything wrong with those 15c 4400mah Zippys? The 5s is $30, it has the most watt-hours per dollar on HK ($0.38), as far as I could tell.

The key is, I am pulling 22amps peak, maybe 17amps for a minute. That's it. So that's 5c peak. For now I am aiming for 150-300w charging, but trying to keep it low cost and simple.

I plan to have two ebikes, one using a 5s friction drive (super lightweight, low power assist for my road racing bike), and my main ebike which will double that to 37v. So I'm thinking of ordering 4 of those 15c packs to get started.

I feel like I need to just get one of those 50w balance chargers on HK, with a simply pc power supply I can find around here.

 

[dogman dan]

There is the b6 ac, that has a built in power supply. Should charge an 80% discharged 4400 5c pack in just under 2 hours, if that is fast enough.

Another reasonably priced charger at HK is 200 watts, and should charge a pack lots faster, but it would need a power supply. And it's out of stock at the moment.

 

[liveforphysics]

That's cool to know if I wanted to spend the money, I could charge that fast.

But if I want to keep costs down, is there anything wrong with those 15c 4400mah Zippys? The 5s is $30, it has the most watt-hours per dollar on HK ($0.38), as far as I could tell.

The key is, I am pulling 22amps peak, maybe 17amps for a minute. That's it. So that's 5c peak. For now I am aiming for 150-300w charging, but trying to keep it low cost and simple.

I plan to have two ebikes, one using a 5s friction drive (super lightweight, low power assist for my road racing bike), and my main ebike which will double that to 37v. So I'm thinking of ordering 4 of those 15c packs to get started.

I feel like I need to just get one of those 50w balance chargers on HK, with a simply pc power supply I can find around here.

Just remember, you get the lower C LiPo, and you're getting the older recipes. Less stability, higher resistance, less cycles etc. I don't know how many cycles you're planning to run, but sometimes the cheapest wh-hr/$ isn't the cheapest in the long run.

Just a few years ago, LiPo technology was limited to a few hundred cycles. Modern forumlas go into thousands of cycles, and the lower resistance means they can feel small fractions of the thermal effects in charge and discharge.

If you're just looking for something to use a few hundred times, go absolute cheapest wh-hrs/$. Sometimes an extra $0.10/wh-hr to get a modern cell type doesn't seem like such a bad idea IMHO.

 

[veloman]

Thanks LFP, I think I will spend a few extra bucks and get something that will last and less likely to cause a fire

 

[dogman dan]

Yeah, LFP knows lipo. I went with 30c turnigy for my first 10 ah of 24s. I want good stuff for the race, and now it's only the moderate good stuff six months later. But I'm going for some cheap stuff for practice laps or preliminary heats. I'm pretty sure I'll do something bad to em along the way racing em, long before I get to 100 cycles. :lol:

 

[dequinox]

I feel like I need to just get one of those 50w balance chargers on HK, with a simply pc power supply I can find around here.

If you go with the ATX power supply like I have, you'll need to modify it to function as a lab supply. Here is a really good link on how to do this...and it even covers the downside of using PSUs for RC charging: http://web2.murraystate.edu/andy.batts/ps/powersupply.htm

PSUs put out 12v very closely, and not 13.8. So when the voltage sags under a high load it can drop below the functioning voltage range of the charger. I've had a few voltage errors because of that, but they have a mod that you can do which will boost the 12v output a little. Perhaps some of the folks on here know better ways to increase a switching supply's output voltage, but I think you're pretty much stuck with what you get. On the upside: it's a really cheap way to go. You can pick up a 300-350watt supply (YES I highly recommend getting a larger wattage because the listed is the INPUT power...not the output. So for a 150w HK charger you want about 300-350 watts) for about $5, and the parts for the modification I did to mine was $6. Not too shabby.

Here's a link to the charger I bought...I paid out the wazoo for the quick shipping and it cost me about $70 total: http://www.hobbycity.com/hobbyking/store/uh_viewItem.asp?idProduct=7523
The downside was it didn't exactly come with a manual, I had to hunt for one on their forums. Also it won't put out 7 amps at its max voltage...but if you do the calculation that would be over its maximum listed power output of 150w. The size is decent and I've found it to be reliable so far.

Hope that helps.

 

[veloman]

Thanks for the suggestions,
Is there a power supply that would well with that Turnigy charger, without having to do mods? I'm not experienced with that electrical circuit board stuff.

Would that be a Meanwell power supply? Or is there something smaller/cheaper that would work?

 

[jdcburg]

I use the AC 8150 with my 8 cell LiFePO4. It works fine so far. I believe HK sells power supplies for that charger. I made one out of a ATX power supply without opening the case. I just cut all the yellow wires and bundled them together, then cut all the blacks (except 1) and bundled them together. I picked up a small 12V bulb and socket for $2 at RS and plugged it into the 5V circuit on the main motherboard plug. You can read about it here http://www.endless-sphere.com/forums/viewtopic.php?f=14&t=19907 I've been using it for a few months and it seems to work fine with that charger - jd

 

[dequinox]

I use the AC 8150 with my 8 cell LiFePO4. It works fine so far. I believe HK sells power supplies for that charger. I made one out of a ATX power supply without opening the case. I just cut all the yellow wires and bundled them together, then cut all the blacks (except 1) and bundled them together. I picked up a small 12V bulb and socket for $2 at RS and plugged it into the 5V circuit on the main motherboard plug. You can read about it here http://www.endless-sphere.com/forums/viewtopic.php?f=14&t=19907 I've been using it for a few months and it seems to work fine with that charger - jd

...what he said Thats the nice and quick way to do it. My way is the sort of medium way...and the one listed on that site I gave you is the meticulous way. I didn't put screw poles on or anything either...but I did open the case.

 

[jag]

You could have a 1kw charger that fits in your pocket.

Show me that pocketable 1kW charger!

(Or give me a design. I've got some 500V FETs and the soldering iron warm...)

I'm guessing a MHz or higher switching frequency might be needed to get 1kW through something the size and weight of a laptop power brick. Might be out of my league for home build...

 

[dequinox]

You could have a 1kw charger that fits in your pocket.

Show me that pocketable 1kW charger!

(Or give me a design. I've got some 500V FETs and the soldering iron warm...)

I'm guessing a MHz or higher switching frequency might be needed to get 1kW through something the size and weight of a laptop power brick. Might be out of my league for home build...

No kidding I'll be glad to know where to find one of those...as long as it doesn't take an arm off in price.

 

[amberwolf]

If you want to design one, you might take a look at http://how2power.com where they have all sorts of design tips and forums and stuff for SMPS design. Most of it is over my head, but I really don't do math if I can help it.