Charging a cache battery from a hub dynamo

[Dave855]

I would ideally like to charge an Anker 2nd Gen Astro 3 10,000 mAh cache battery from a Son 28 dynamo hub. My first question is whether this is a reasonable set up up whether the battery is just too large....maybe the Anker 2nd Gen Astro 6700mAh would be a more sensible option?

I am also unsure whether either of these batteries would effectively trickle charge from a hub dynamo. With a USB charger such as the Sinewave Reactor or Tout Terrain Plug iii, would this system work? Or would something like the E-Werk be necessary which can be altered to provide a higher voltage into the battery?

Can anyone shed any light on this...

Thanks,

David

[andrew_s]

It won't make any difference whether you get the 10,000 mAh version or the 6700 mAh version, other than it will take longer for the 10,000 mAh version to reach full charge.
Charge rates will be similar to what you'd get charging from a computer USB port, rather than the mains. You may get a faster charge with an eWerk set to 5.6V with the maximum current (1.5A) if you ride fast enough, but don't count on it.

[[XAP]Bob]

the Ewerk will get you a more regulated voltage, which might be useful - but I guess the batteries will self regulate (by taking more power when it is available)

I have a commercial version (Biologic ReeCharge) which does a decent enough job.

[jb]

Depends on where you expect to use it and what speed you generally maintain. In steep hilly terrain with a heavy load you don't get much charge at all, ie the downhills don't compensate for the uphills.

[jochta]

I use an E-werk to charge a small Anker battery (Anker Astro E1 5200mAh) to then use to charge phone, Garmin etc. when stopped.

[ConRAD]

IMO, forget the 10000 mAh (i.e. 37 Wh whether using a 3.7 V Li-ion battery) and try, without guaranteed success of course, its smaller version rated 6700 mAh (i.e. 25 Wh)

Rule of thumb: something around 5000 mAh should be the top limit … above it, available power might not be enough, voltage might be likely to drop …. etc. etc.

[Dave855]

I read an account on the Bicycle Wanderer blog that the Sinewave Revolution (same 5v output as the Reactor or The Plug etc) was unable to charge an Anker battery....at least at anything more than a trickle charge. I'm not sure why this would be though and whether it is specific to Anker. Are there any other cache batteries that are effectively charged at 5 volts and under?

There are accounts on this forum of people using the E-Werk to charge decent size cache batteries. Assuming you set the E-Werk at it's highest output of 13,3 Volts, presumably this would always give a better charge to a cache battery than any of the competition (regular Werk, Revolution, Reactor, Plug etc) because they all max out at 5 Volts. Am I right in this theory?

I also came across an account of someone (on the Tired of I.T blog) who was able to charge their laptop using the E-Werk by adapting a laptop charging lead designed for use in a car. Again they utilised the higher voltage setting on the E-Werk. Does anyone have any experience of doing this?

Thanks,

Dave

[andrew_s]

Most cache batteries are designed so that they will charge off a computer USB port, or any other USB power supply. If it's 10,000 mAh, it takes twice as long to charge to full as 5,000, but size doesn't otherwise make any difference.
It's only things that come with a mains adapter and no USB charging lead that are difficult, and for which an eWerk is better than other things, provided that the mains charger voltage isn't over the max 13.3V of the eWerk. For example, CJ (OTP) has reported success charging a 7.2V Olympus camera battery with an eWerk set to 8.4V and max current. 4.2V per cell is near max charge on a Li-ion battery, so charging at that constant voltage is fairly safe, even if you only get to about 80% full.
I'd expect an eWerk set to 13.3V and a car battery charge lead to work, but slowly. Most of the time you won't be riding fast enough for the eWerk to give much current at 13V.

[Samuel D]

There are accounts on this forum of people using the E-Werk to charge decent size cache batteries. Assuming you set the E-Werk at it's highest output of 13,3 Volts, presumably this would always give a better charge to a cache battery than any of the competition (regular Werk, Revolution, Reactor, Plug etc) because they all max out at 5 Volts. Am I right in this theory?

No. You can’t just increase the voltage to charge faster. That quickly becomes dangerous with lithium-ion batteries. If I wanted to charge a battery pack that accepted power via USB port, I’d just get the USB-Werk. Busch & Müller makes a cache battery for the E-Werk if you prefer the flexibility of powering different things with the latter. I’d opt for the B&M battery over a third-party one unless there was a very good reason to need a different energy capacity.

[jochta]

There are accounts on this forum of people using the E-Werk to charge decent size cache batteries. Assuming you set the E-Werk at it's highest output of 13,3 Volts, presumably this would always give a better charge to a cache battery than any of the competition (regular Werk, Revolution, Reactor, Plug etc) because they all max out at 5 Volts. Am I right in this theory?

No. You can’t just increase the voltage to charge faster. That quickly becomes dangerous with lithium-ion batteries. If I wanted to charge a battery pack that accepted power via USB port, I’d just get the USB-Werk. Busch & Müller makes a cache battery for the E-Werk if you prefer the flexibility of powering different things with the latter. I’d opt for the B&M battery over a third-party one unless there was a very good reason to need a different energy capacity.

Note that the B&M cache batteries don't/won't last long (I have experience of this) if you are using them to buffer the charge between the E-werk and your devices. Batteries don't like doing pass-through charging. For exactly that reason some Anker batteries deliberately prevent you from doing this to prolong the life of the battery.

[phil parker]

I'll try and keep this reply succinct and I respond with a lot of experience, three bikes with Schmidt dyno hubs & Ewerks fitted and 1000's of touring miles under my belt...

I've found the best compromise for a cache battery to be about 5000 mAh. I sometimes use a 3500, and that will fully charge after an average day (I try & pick 80-mile days depending on terrain/weather) and be enough to charge my Garmin and my phone during the evening. My 5000 cache battery will not fully charge if I have a short day.

So in answer to your question - a 6700 cache may be ok, but I wouldn't use. 10,000. (From previous experience).

[andrew_s]

Why do you worry about whether the cache battery is fully charged or not?
If you put 5000 mAh worth of charge into a 10,000 mAh battery, you have exactly the same available energy as you do with a full 5000 mAh cache battery.
The difference is that if you reach 5000 mAh part way through the day, you can't store any more with the smaller battery.

[RickH]

Plus if you start with a full 10,000mAh you've got all that charge "in the bank" & simply top it up as you go along (literally).

Rick.

[phil parker]

I need to elaborate further...and I will stand corrected if wrong, but I'm quite certain that the 10,000 mAh cache battery I used required a higher input charge than I could provide from my dyno hub set up and the reality was that insufficient charge was going in to create any supply - like the difference between charging an iPhone or an iPad. The 3500 and the 5000 were sufficiently small enough to take a good charge from my set up and be able to give me a good supply in the evening.

I can't remember the composition of the battery and perhaps some of the modern Li-Ion will recharge on a low current?

Regardless of which, I would certainly check that first

[edocaster]

It's certainly plausible that a higher capacity battery may be 'harder' to charge - not just to full capacity, but in any useful way.

While it's possible to make a 10,000mAh USB battery to behave as two 5,000mAh batteries - charging sequentially - in most cases manufacturers won't do that. They will just either use more cells working simultaneously (in parallel or series - not really that important as they undergo DC-DC conversion anyway), or larger cells. Essentially, the 10,000mAh pack basically behaves as, and is, a 'larger battery.'

Battery charge and discharge rates for particular chemistries are often referred to in terms of 'C' - i.e. amps in relation to the capacity of the battery in amp-hours. So you might read that C/20 is a 'safe' rate to trickle charge NiMH cells, or that a good Li-ion battery can withstand a 2C discharge without voltage sagging or cell overheating. In other words, the absolute figures are proportional to the capacity.

So larger batteries can often discharge at higher absolute currents, but also may be designed to charge optimally at higher currents and just fail to charge at low current rates. Much like how a large engine may need a more beefy starter motor and battery to turn it over.

Given the choice, I would typically take two separate 5,000mAh packs over one 10,000mAh pack.