There’s merit in having small batteries. Don’t necessarily go large…

[Cisco-man]

Having spent a few months using relatively small Swytch battery packs, I bought a rather large 15Ah Yose battery pack.

I can now see merit in having smaller packs available, as firstly they charge a lot quicker - I’m conscious that it’s best-practice not to keep partially charging as the BMS balancing never kicks in. A smaller pack also is more easier to carry around when you get to where you’re going.

With my Yose pack I find that I come back from a trip out, I seem to have too much charge (voltage) left in the pack. I’m not comfortable storing it away with 40v plus still in it, and I’ve been at a loss as to how to lose some power before I store it away (apart from going on another ride).

I’ve made up a load resistor using a 50 ohm 100w resistor (from ebay) on a heatsink (it gets hot), and it discharges the battery at a leisurely 0.8A so I can soon get the charge down before I store the pack away. The blue thing in the picture is just a cheap volt/ammeter to monitor what It’s doing. I have wired my bikes so that I can use the small swytch packs too if I want.

 

[Nealh]

40v or a little above is not an issue it is at approx. 78 - 80% so not in a fully charged state.

 

[saneagle]

Larger batteries have a larger voltage, so you get more power. The difference in power is about 10% for a ride long enough to flatten a small battery.

 

[Cisco-man]

40v or a little above is not an issue it is at approx. 78 - 80% so not in a fully charged state.

Good to know. I was thinking 38v was a good target, but happy to be corrected to 40v!

 

[Nealh]

38v is often for longer term storage when not in use but typically was more associated with lipo cells.

 

[Saracen]

Small batteries may.............. may have a place but I would find the drawbacks, especially range very limiting, my nearest village is 14 miles return, 40 miles to town and back

 

[Cisco-man]

I like the immediacy of the swytch packs. It was a nice morning, so at 8 o’clock we decided to bike the eight or so miles to a pub at Otterton. By 10 o’clock the batteries were charged and ready. My big pack would’ve taken four hours to fully charge. I’m now wondering if my Yose pack would be ok with a 4A charge-rate, but anyway, for sixteen miles it’s overkill. Small packs have there place.

 

[Az.]

If you keep discharging battery through your gizmo, you shorten it's life.

Yose batteries have poor size to capacity ratio. My Yose 36V 15Ah battery is the same size as 48V 17,5Ah.

Sag is also a problem. But I know what you mean. I don't like huge batteries either.

 

[Bikes4two]

I’ve made up a load resistor using a 50 ohm 100w resistor (from ebay) on a heatsink (it gets hot), and it discharges the battery at a leisurely 0.8A so I can soon get the charge down before I store the pack away. The blue thing in the picture is just a cheap volt/ammeter to monitor what It’s doing. I have wired my bikes so that I can use the small swytch packs too if I want.

• With the addition of a few cheap components you could extend your load resistor project to give you more battery information to help you understand the performance of your battery and what range each of them is likely to give you under different riding conditions.
• Below is the schematic of my battery test rig which only differs from yours by the inclusion of the XH-M609 module which I set to a cut-off voltage (LVC) of 30v (for when testing my 36v battery packs,
• So periodically I fully charge the battery and then discharge it through the load resistor via the XH-M609 until reaching LVC and noting the Ah and Wh recorded on the watt meter. This is then the benchmark for any subsequent tests to ascertaining the inevitable aging of the battery pack.
• However, I have a more often use for this test rig and this is to ascertain how much battery energy I've used for different rides - let me explain:
• You'll have to imagine this as I haven't a diagram for this configuration but here goes
  - disconnect the battery from the watt meter input
  - disconnect the resistor load from the watt meter output
  - connect the battery to the watt meter output
  - connect the battery charger to the watt meter input
  
  You now have an arrangement that records how many Ah and Wh you put back into your discharged battery (parially or otherwise) and if you note these readings against miles ridden for that ride and maybe the terrain/pace covered, you quickly build up a profile of how many miles you can expect from what ever battery you might be using.
• That's it in outline - in practice how you mount the various components, plugs, sockets and so on, is down to you but I re-charge my batteries after every ride using the test jig and note the Wh/mile - so far after over a year on my self build battery packs, there is no appreciable degradation as yet although it will eventually happen but I should be well placed to spot it happening.
• Of the three self build batteries that I have (1x 8.4Ah and 2x 4.2Ah) I am able to determine which combination of batteries I need for the longer rides resulting in me not carrying unnecessary battery weight.

 

[Cisco-man]

Thanks. I like your style - I love a good spreadsheet! I shall read and absorb…

 

[Nealh]

Small batteries have a place on EAPC's , it simply depends on the use , terrain and power one needs.

 

[Peter.Bridge]

Just converted a 12.5kg folding bike, 1.6kg front hub motor (akm-74sx) + KT controller &display+ 36v 10ah Woosh battery bag( 1.8kg)

Just makes it light to lug around stash away & get out. I'm not so sure the extra weight of an electric bike (or bigger battery) makes that much difference when you are riding it

 

[AntonyC]

The smaller battery may not charge faster, it just reaches full sooner, but a ride doesn't have to start from full. If the Yose arrives home having used 2V of its 42V it's ready to make that trip a few more times, so its immediacy is better than the smaller battery: you could charge it once a week.

 

[Cisco-man]

The smaller battery may not charge faster, it just reaches full sooner, but a ride doesn't have to start from full. If the Yose arrives home having used 2V of its 42V it's ready to make that trip a few more times, so its immediacy is better than the smaller battery: you could charge it once a week.

Fair point. It may be just a matter of gaining confidence with each pack. I always charge to full before a trip - because I then know what the battery has to give, and how far it will get me. A half-charged battery is an unknown to me at the mo.

 

[Cisco-man]

• With the addition of a few cheap components you could extend your load resistor project to give you more battery information to help you understand the performance of your battery and what range each of them is likely to give you under different riding conditions.
• Below is the schematic of my battery test rig which only differs from yours by the inclusion of the XH-M609 module which I set to a cut-off voltage (LVC) of 30v (for when testing my 36v battery packs,
• So periodically I fully charge the battery and then discharge it through the load resistor via the XH-M609 until reaching LVC and noting the Ah and Wh recorded on the watt meter. This is then the benchmark for any subsequent tests to ascertaining the inevitable aging of the battery

I’ve ordered up my MH-609 circuits (ebay, two for six quid). I shall baseline all my packs in the way described.
I’ve had a few battery packs (from a couple of swytch bikes I’ve now converted) and I really don’t know how capable they still are, so this will help me take a view on that.

 

[Nealh]

My LG hg2 drinks bottle battery is <1.45kg , layout is 12s 2p .
6ah/264wh, 25a continuous / 40a for short bursts and good for up to 30 miles or more for flat terrain riding in PAS 1 .
A battery can be anything you want it to be depending on the chosen cells and layout.

My other slim battery is the Molicell p42a, 12s 2p 8.4ah/369wh, 30a contiuous /50a for short bursts. I haven't carried out a range finder for this one but would expect 40 miles or so. Towing my trailer with the Ute it has managed 24 miles with some to spare.

If one is a frugal power user then light small battery might be the answer though will likely be a bespoke build with cells of ones choice.

 

[guerney]

My bike cares not about weight. The trailer haul uphill capability enabled by my 19.2Ah/691Wh battery outweighs the mertis of going small. The absence of range axiety if also a big plus.

My other slim battery is the Molicell p42a, 12s 2p 8.4ah/369wh, 30a contiuous /50a for short bursts.

Wow, that's a lot of continuous amps from such a small battery. What would 10s 6p be capable of? Here's a Molicelled supercar:

 

[Nealh]

My P42a info was a bit on the low /conservative side.
Continuous more like 40a & 60a bursts.

With 6p one can easily ask for 110 -120a .

The advantage of small batteries using high current cells is little or no stress when using higher current , drawing 20a is only taxing the cell by 33%.

 

[Nealh]

My swizzbee has a panny 9p & HE2 6p battery in parallel, max current draw is 210a or approx. 140a continuous. 39a is the most I have seen from the ammeter reading.

 

[guerney]

The advantage of small batteries using high current cells is little or no stress when using higher current , drawing 20a is only taxing the cell by 33%.

Should be even less stressed in a larger pack, which I guess would result in longer battery lifespan. It's a pity there aren't any ready made ebike batteries made using those Molicells available from any seller.