Portable Range Extender

[longwise_suck]

So though i love my E-bike I despise range anxiety.. I have tried the eco riding on longer trips, when faced with a headwind a lot of hills or you just want to be a spanner you can find yourself a long way from home with a almost empty battery, so I tried a trailer that was a mobile solar charging station, i tried carrying more batteries but to be honest on a 85k round trip I dont need more weight that shortens my range as it is so i built this


its bassicaly a battery powered charger, 6 to 60 volts in 10 to 80 volts out, it can charge at about 4 amps an hour without getting to hot, on the left volts in are displayed in the middle amps out on the right volts out, on the front panel is a port for volts in from my 18 volt PSU one the left, and on the right is the port for charging, on the back is a port for battery operation, this is a prototype in the future i plan to use 18650 5s4p built in with a charging port and better cooling.

Today was the first test for it i rode the bike too hard for too long so whilst I sat at a cafe drinking my coffee outside i plugged in the batteries to the charger charger to the bike and got the cells from 3.92 to 4.15 more than enough for the 30 km ride home.Next year I have a biking holiday planned for summer 2017 Frankfurt to Berlin 540 km with the route i have chosen the problem has always been range and where i can charge the bike, with this I do not have to worry about charging in the middle of the day so much and i can charge directly instead of using a balance board, hope this idea is useful for someone.

 

[gogo]

i tried carrying more batteries but to be honest on a 85k round trip I dont need more weight that shortens my range

its bassicaly a battery powered charger

^These two statements seem a contradiction.

The best way to use extra batteries is in parallel with the rest. Extra batteries should never shorten your range. Using an extra battery through a charger to charge another is wasteful in comparison to just putting them in parallel or even using them serially one after the other, especially if you have to carry a dedicated charger.

 

[longwise_suck]

Not when the 2 batteries in question are too weak to keep up with the pack, they are old multistars that never really made the ebike grade

 

[ulrichw]

[...] On a 85k round trip I dont need more weight that shortens my range as it is so i built this[...]

Try this "Gedankenexperiment":
- Weigh your charger + battery combo
- Weigh your battery
- These two weights added together are the total weight you are carrying on your ride
- Now create a new battery that is the same weight as this total.

Which one will give you a longer total range? (All other conditions being equal, of course).

Hint: The second law of thermodynamics is not your friend.

 

[gogo]

That's a clever way to utilize marginal batteries.

 

[longwise_suck]

That's a clever way to utilize marginal batteries.

ha thanks they just sit there doing bugger all, eventually i will run a set of 18650s in there they are a lot lighter but for now this set up works as an emergency back up in a ruck sack

 

[dogman dan]

The only thing that makes sense here to me, is you can take batteries of one voltage, and charge batteries of another voltage with them. Well, maybe two things, you can charge while you ride with this too.

But if you have an old sucky 14s pack, and a new nice 14s pack, no matter how saggy those old ones are, you can parallel them and use em. As long as they aren't shorted, puffed, leaky or dangerous, you can still use them.

once paralleled, they will add what they can, but at a low c rate, which will max out their usable capacity. This is what I've done for years, when I needed 80+ mile range. Part of the pack I'm paralleling, is pretty rank, about 50% capacity if used by itself. But even if it's just 5 ah more from a 10 ah pack, it's still another 250wh farther down the road. In most cases, I'll still get about 70% capacity from bad old packs if paralleled with enough other battery. The key thing is taking the wh from the bad stuff, at less than .5c rate.

 

[parajared]

Interesting: so if I'm understanding this correctly your amperage demands exceed the C rating of your 18650 pack (too much amperage for the battery to handle). So the weight of your charger is less than the weight of simply adding extra batteries to get the C rating needed?

 

[longwise_suck]

Right, the pack I have are LiHV multistars, they don't go with anything I own and on their own they suck, so for now i used them in this idea, later I will use 18650s to keep the weight down, the point of this is i can charge both of my bikes and the wifes bike 60 48 and 36 volts respectively, plus i can use a variable power source, so batteries, my power pack or a car battery so its quite versatile and currently uses 2 batteries i have no use for

 

[MadRhino]

I see it like I was carrying a water pump and an extra can of water, only to refill my water bottle.

 

[pdr]

But if you have an old sucky 14s pack, and a new nice 14s pack, no matter how saggy those old ones are, you can parallel them and use em. As long as they aren't shorted, puffed, leaky or dangerous, you can still use them.

once paralleled, they will add what they can, but at a low c rate, which will max out their usable capacity. This is what I've done for years,

Putting batteries in parallel must be the best thing reducing the current drain from both and increasing you range. Perfect, many gents and dames are looking for this, the golden egg, the way to maximize ecologically the lifetime of a battery which would not serve stand-alone,
BUT: it is not simple connecting in parallel, there is something more to it. To start with how to coop with (unintended) difference of voltage?
And secondly, once you prevented flow from on battery into another, is there any other risk of a just plain parallel connection of two different batteries, let us say, for example
a new 15Ah 36V 2C lithium battery 100% charged together with
an old 10Ah 36V 1.5C lithium battery 80% charged and of slightly different chemistry?

So please which basic circuitry (only diodes?) is needed to have it save, simple and functional? Could you hint us, newbies, on that, dear Dogman Dan?

 

[amberwolf]

To start with how to coop with (unintended) difference of voltage because of different SOC?

If they're in parallel:
--and each has it's own BMS with separate ports for charge and discharge (and when it shuts down it doesn't allow charge thru the discharge port)
--and you've charged them up to full
--and made sure they're balanced before you start
then you don't have any worries about this.

If you can't do that, and you still want full isolation of one from the other, then you can use diodes of sufficient current and power dissipation capability for your system, with the anode (back of arrow marking) at the + of each pack, and the cathode (tip of arrow marking) at the + input to the controller, to prevent any possible backflow from one into the other.


If neither pack has a BMS you will have to monitor each one manually somehow to know what state of SOC they are in; what you ahve to do depends on the kind of pack, and that you'd have to research.

And secondly, once you prevented flow from on battery into another, is there any other risk of a just plain parallel connection of two different batteries, let us say, for example
a new 15Ah 36V 2C lithium battery 100% charged together with
an old 10Ah 36V 1.5C lithium battery 80% charged and of slightly different chemistry?

As I said before, they need to be the same SOC and chemistry if you want to be sure of paralleling them easily.

IF they are not, then you can isolate them with diodes as noted above.

Either way, always start with the same SOC.

 

[dogman dan]

Yes, of course they need to be same state of charge, same fully charged voltage too, meaning a 13s "48v" can't be paralleled with a 14s "48v".

But, with some paying attention to the stopping point voltage, you can parallel a 14s lipo with 16s lifepo4. Not easy, or care free, but definitely possible.

As I said above, the one logical reason to use one battery to run a charger to charge another out on the road, would be to cope with big voltage differences. Otherwise, it is like carrying a pump to pour water from one jug into another.

It's also one of the ways, not the best, to get from say, 12v solar panel input, to a 48v bike battery. panel to 12v battery, to charger, to traction battery.

 

[keithmac]

Diodes aren't a good idea really, you lose at least 0.7v through them which is a fair bit of range by all accounts?.