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Questions about expanding the battery in a RS HS


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Hi everyone! I've ordered a Gotway/Begode RS HS as my first wheel (I rented a Tesla V2 for a week and fell in love with the hobby) and the only thing I'm concerned about is the range (it won't affect me often, except occasionally with a group I've joined that does weekend group rides and I'll be keeping up with EX.Ns and Shermies, the odd ride may exceed my range and I'll have to break off early) and the close amperage tolerance of the 4P configuration of the batteries. I would have gone for the EX.N if I had the extra 1100 CAD to make the purchase, but the RS was the only option that met my desire/cost balance. 

I'm looking into building an auxiliary pack (also using the m50T batteries, no sense in mismatching) and while I have a comfortable understanding of the cells themselves (avid vaper, learned all about the 18650/20700/21700 batteries) and I have a diy/electrical/electronics background and am comfortable with my ability to build a safe pack, I am not quite sure how the BMS in these wheels works and am hoping you guys can clear this up for me.

In installing a battery pack, are there terminals on the existing BMS that I can tie my aux pack (probably 24S1P as I will struggle to fit more into it without significant chassis modding) into, or will I need to buy an additional BMS board and slave it to the existing BMS? Is the stock BMS located within the wrapped packs, or alongside the motherboard for the wheel? Please help me understand how the system works so that I can develop my upgrade plan.

I'm sure that the additional 25% range will be enough until I'm ready to mod the chassis and add another 25%, and the additional 25% tolerance in terms of battery draw will make me feel much more comfortable, as the m50T is a pretty low-rated cell in terms of draw.

Thanks in advance for the help and insight you offer!

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My understanding is that most wheels have a BMS for each pack - although mine is unusual in that it has only one BMS which handles the cell groups in both packs by way of an 11-pin connector (two 10s4P packs of M50T cells). Having a separate BMS in your auxiliary pack is probably the easiest way to go. I don't know enough about how they work to know if you might run into issues having BMSes with different specs - i.e. low voltage protection circuits etc. There may be exceptions but all the wheels I'm familiar with have BMSes contained inside the packs, alongside the cells, all wrapped in heat-shrink. There are some nice looking options for 'Smart' BMSes that will communicate individual cell group voltages etc. via Bluetooth but you might need some extra space in the wheel to fit them.

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4 hours ago, kiduxek said:

In installing a battery pack, are there terminals on the existing BMS that I can tie my aux pack (probably 24S1P as I will struggle to fit more into it without significant chassis modding) into,

One could most probaly. But this includes opening the wrapped pack and bringing 25 wires safely to your new pack and then pack everything again.

4 hours ago, kiduxek said:

or will I need to buy an additional BMS board and slave it to the existing BMS? Is the stock BMS located within the wrapped packs, or alongside the motherboard for the wheel? Please help me understand how the system works so that I can develop my upgrade plan.

With an own BMS it has to fit with the other two BMS (and maybe the motherboard). Here are the details of gw bms used in 2015:

https://forum.electricunicycle.org/topic/18374-how-bms-works-gotway-pack-teardown/

Most probable they changed the used bms inbetween, but you get an idea of what to consider.

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Posted (edited)

It will be much easier to use a stock Gotway 24s bms. They are available and not overly expensive.

The only issue I can see is running a 1s pack in combination with 2x 2p packs. I would be wary.

I believe that when you increase the capacity of any wheel you need to keep the same S rating so that everything discharges at the same rate. Even more important if you charge all the packs together is that they charge at the same rate. This charge issue may not be a consideration though if you will be charging your extra pack separately.

Ideally you need to make a 24s2p pack. I appreciate this is a hassle to carry but at least it will be singing from the same hymn sheet as your existing packs.

Edited by Planemo
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3 minutes ago, Planemo said:

The only issue I can see is running a 1s pack in combination with 2x 2p packs. I would be wary.

 

3 minutes ago, Planemo said:

Even more important if you charge all the packs together is that they charge at the same rate. This charge issue may not be a consideration though if you will be charging your extra pack separately.

No, neither is an issue. Currents divide according to the "internal resistance". So the 1p pack automaticly gets and delivers only half of the 2p packs.

Nicely matched cells and eager balancing are the important part.

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18 hours ago, kiduxek said:

Gotway RS HS

I'll be keeping up with EX.Ns and Shermies

additional 25% range will be enough

It's not enough... +25% is so much work for so little improvement :(

Leave your wheel stock, and throw 1000wh+ in your backpack.
There's no off-the-shelf 100V auxiliary pack available right now, but you just said you're willing to embark on a DIY pack... so this job will be easier than what you planned ;)

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7 hours ago, RagingGrandpa said:

It's not enough... +25% is so much work for so little improvement :(

Leave your wheel stock, and throw 1000wh+ in your backpack.
There's no off-the-shelf 100V auxiliary pack available right now, but you just said you're willing to embark on a DIY pack... so this job will be easier than what you planned ;)

Hmmm, you really think it's too poor a return for the effort? I'd go for a 50% improvement, but that would involve even more effort.. based on my reading, I'd be looking at (re)moving the speakers, and possibly beeper, to fit more. I would consider investigating a custom side panel though, I know someone with a 3d printer who would love to print me some PVC or rubber compound panels. Maybe I could create integral, literal, power pads lol.

How does the backpack idea work? Do you connect it to the charge port on the EUC or do you need to connect to the internal harnesses? I would consider something like that or a battery box to carry in my EDC for long rides. I would probably prefer a ride-then-charge configuration as I'm fairly new to the scene and will still spend a lot of time wiping out while I learn the more advanced skills, and don't think I want to be tethered to my machine via an electrical connection to a lithium bomb.

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You can do all that or go the easy route & sell the RS to get the EX.N. Its possible the upgrade won't cost much more than the diy battery pack once time, effort & materials are taken into account. Plus as we all suspect, the risk of thermal runaways increases exponentially with home brew Li-io paks.

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Yeah, you're probably right. Well, I'll hone my skills on the RS and then in a year or two maybe look at whatever the latest and greatest in the EUC world is at the time. Or buy a year old EX.N used.

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The RS should have enough space on the left side if you remove the RS lighted logo and beeper. Using a Begode stock 900wh pack with bms would be simple. Just make a new collector harness and relocate the beeper. If you make a new pack use better bms modules for all of the packs. I'm contemplating doing that to mine. I don't know the resale value for an RS. I like some things on the EX.N and some things not. 

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@Unipilot69 that's not a bad idea. I'm contemplating forgoing the speakers entirely, I could move the beeper to the other side of the wheel, removing the speakers, and put the 900 wh pack into it. That would push me out to almost 70 km of range under aggressive riding conditions and over 100 if I'm economical with it.

The appeal of 6P battery configuration is high as well.

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Posted (edited)

I have not regretted it, even if it is only 25% more and I would do it again anytime.

21700 Samsung 50E cells and this BMS

I charge sometimes with 9A without problems. (knock on wood) :efee612b4b:

20210115-181354-01.jpg

Screenshot-20210504-082854-Whats-App.jpg

Screenshot-20210504-082813-Whats-App.jpg

Edited by EUC Custom Power-Pads
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Posted (edited)
7 hours ago, EUC Custom Power-Pads said:

(2250wh MSP)

I have not regretted it, even if it is only 25% more and I would do it again anytime.

More capacity is always more fun... but @kiduxek set a pretty high bar with the goal of "keeping up with EX.Ns and Shermies."

I'm in the same boat- trying to stay groupride-compatible with Shermans.
In my experience, 2250wh is good for 35 miles at 30mph, which is significant. And 2500wh for about 40 miles.
But those Sherman guys are good for 45 miles+ (and cruise comfortably at 35mph) so if they're out for a normal 2hr ride, your 2250wh wheel will be left at the roadside 10 miles before the end :(

  

9 hours ago, kiduxek said:

I'm fairly new to the scene and will still spend a lot of time wiping out

don't think I want to be tethered to my machine via an electrical connection

Easy to include a breakaway connector in the cable... but I agree, tumbling with a battery in your backpack is something to avoid.

But that's the beauty of the backpack- use it only when you need it. If you're "trying new things," no backpack. Later when you need to groupride with 2700wh EUCs, put it on.

(Hopefully you're not chasing down EX.N's if you haven't already gotten comfortable sustaining 30mph from practice on your own... you shouldn't be crashing when riding with the group, spoils the mood :P. Go practice first!)

Edited by RagingGrandpa
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Yes, keeping up with Shermans at higher speeds is impossible. :D

You are right, with 2250wh I can reach 35-40 mi with high speed and aggressive style @80kg rider weight and no headwind, but with a knobby tire @1.4 psi offroad. Maybe with a street tire, higher tire pressure and on road a little more. 

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21 hours ago, EUC Custom Power-Pads said:

I have not regretted it, even if it is only 25% more and I would do it again anytime.

21700 Samsung 50E cells and this BMS

I charge sometimes with 9A without problems. (knock on wood) :efee612b4b:

 

Hmm, it does look pretty tight hey? Definitely no room for more than 450Wh in there is there?

 

13 hours ago, RagingGrandpa said:

More capacity is always more fun... but @kiduxek set a pretty high bar with the goal of "keeping up with EX.Ns and Shermies."

I'm in the same boat- trying to stay groupride-compatible with Shermans.
In my experience, 2250wh is good for 35 miles at 30mph, which is significant. And 2500wh for about 40 miles.
But those Sherman guys are good for 45 miles+ (and cruise comfortably at 35mph) so if they're out for a normal 2hr ride, your 2250wh wheel will be left at the roadside 10 miles before the end :(

  

Easy to include a breakaway connector in the cable... but I agree, tumbling with a battery in your backpack is something to avoid.

But that's the beauty of the backpack- use it only when you need it. If you're "trying new things," no backpack. Later when you need to groupride with 2700wh EUCs, put it on.

(Hopefully you're not chasing down EX.N's if you haven't already gotten comfortable sustaining 30mph from practice on your own... you shouldn't be crashing when riding with the group, spoils the mood :P. Go practice first!)

Mostly the group is doing sub 30 mph speeds, closer to 20 mph, and they top out around 30 mile rides except for the rare 40-45 mile trip.

You're right about when to use the backpack. Stunt riding and distance cruising are two totally different situations. Realistically the times that I will need more than 30-40 miles of range are pretty few. I have time to engineer an elegant solution I'm sure.

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1 hour ago, EUC Custom Power-Pads said:

Simply connect in parallel to the other two batteries and charging ports. 

Fyi - be aware that paralleled packs need synchronisation. If one pack cuts off charging once in because of imbalances one cell (group) gets overcharged the other good back will keep charging this "bad" pack!

So there is real risk of overcharging individual cells, once packs gets (aged and) out of balance.

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7 hours ago, EUC Custom Power-Pads said:

connect in parallel to the other two batteries

I presume it's like we discussed below?

https://forum.electricunicycle.org/topic/17404-i-got-an-msuper-pro/page/2/?tab=comments#comment-301858

 

40 minutes ago, EUC Custom Power-Pads said:

between the original battery packs no synchronization takes place

No. It does.

The (two or more) Gotway packs tell each other to stop charging if there is a problem in any one pack. More here.

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49 minutes ago, EUC Custom Power-Pads said:

Without knowing it exactly, but I mean that between the original battery packs also no synchronization takes place. 

Kingsong has such synchronisation since the KSxxS series, before it had some kind of daisy chain config so sync is not needed.

GW also already had such sync in 2015 (https://forum.electricunicycle.org/topic/18374-how-bms-works-gotway-pack-teardown/) - very, very likely also before. And/or something like the dausy chaining.

And before were just single packs.

There were never (to my knowledge) systems on the market that would override single cell overvoltage protection while charging! Hopefully also not the 3rd party modded GW from aliexpress resellers.

From my readings somewhere around 4.3x li ion get extremely unhappy during charging - and this are voltages easily reached by imbalanced packs during forced, unprotected charges - like with unsyncronized paralleled packs!

Be happy that your mod worked out till now (all packs balanced) and start to plan a change!

 

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