How crazy am I

[cooking monkey]

I have now been able to rack up some km on my new voltbike. Enjoying it very much and learning lots of little things.I have observed that out of the gate with a full charge on the flat I top out at around 38kmhr. By the time I am down to 44 volts I have fallen to a top speed of about 28kmhr. Speed appears to track voltage in a linier way. I started thinking that if when the voltage had fallen down to say 46 volts that it would be nice if I could switch in another // grouping of cells to add 4 volts on demand. Is this a crazy idea, some reason I shouldn't do this? My battery pack is 16amphrs at 48 volts, controller is limited to 15 amps from the pack (but can be set for 20)I thought of building a pack of 6? 18650 cells in //. That should put me in the ball park? any ideas?

[Chalo]

Don't do it. You'll only be tempted to run your main pack down to its low-voltage cutoff, which is abusive to it.

If your pack is 13S (48V nominal), then you can add a 1S supplementary pack of the same capacity (16Ah) for the entire discharge-- not just the end of the main pack's discharge. If your pack is 14S (52V nominal), well, enjoy it the way it is. Your controller would probably be harmed by 15S fully charged voltage.

[amberwolf]

No. Adding a set of charged cells in series with a discharged battery doesn't get you anything; the discharged battery is still discharged and still has to be recharged.


EIther:

Get a bigger battery (more Ah, same voltage) to replace the one you have,

Or

add a second battery in parallel with the first.

You could also swap out the discharged battery for the charged battery at the point it runs down too far, but the systme will perform better if you parallel them both at the same time. (just disconnect them when charging, and charge them separately)

[dogman dan]

Well, I've done what you did, and it did make me fast. But the key thing is this, don't do it in a way that makes your main battery get too discharged.

Here is what I used to do, I had a 12 mile round trip to sams club, downhill. About 1000 vertical feet to the valley where the store is. I had a 10 ah 48v pack. Going down, i'd run about 30 mph the whole way. Plenty fast down the hill. But coming back up, towing a very heavy trailer, it was a crawl, and possibly not enough battery to make it. So to return, I added a 24v 5 ah pack. The controller was compatible with 36-72v, so no problem there. I'd zip up the hill home, but since I only used about 4 ah coming down, I was adding 5 ah more 24v, to about 6 ah of 48v. With the extra capacity for that steep climb home, I would definitely make it, without running out of capacity on either the 48v or the 24v pack.

So if you have a 16 ah pack, add 8 ah of one cell more at the middle, so both run out about the same time, and stop well before either one empty.

But realistically, what you really crave is a battery that is higher voltage at the start, and then has decent volts later. This is why I greatly preferred a 14s "48v" pack vs a 13s. 14s I started out 4v higher. Most 48v controllers can handle 60v, so most likely your best bet is to add a paralell cell group of 16 amp hours size for the whole ride, if your pack is 13s, charging to 54v. Connect in series, downstream from the bms. The pack will stop running when the main pack cells are drained, and hopefully, before your boost cell pack does too.

[cooking monkey]

Lots of good advice, thanks. I am still learning about these things so I will be a while before I act.

[markz]

If you want a minimum amount of speed, then you have to get more battery in series with the same amp-hour capacity. You take your current battery, if it be 13S and you get another 2S and you take the ground of the 13S connect it up to the controller, the red postiive of the 13S pack to the 1S or 2S black negative wire, and the 1S or 2S red positive to the controller. Then you need to find a way to charge that extra 1S or 2S that you added. Be sure that the 1S or 2S has the same Ah (Amp-Hour) capacity, preferably the exact same cells but others have done it with various different batteries. Key factors is the Ah and same chemistry.

[cooking monkey]

If you want a minimum amount of speed, then you have to get more battery in series with the same amp-hour capacity. You take your current battery, if it be 13S and you get another 2S and you take the ground of the 13S connect it up to the controller, the red postiive of the 13S pack to the 1S or 2S black negative wire, and the 1S or 2S red positive to the controller. Then you need to find a way to charge that extra 1S or 2S that you added. Be sure that the 1S or 2S has the same Ah (Amp-Hour) capacity, preferably the exact same cells but others have done it with various different batteries. Key factors is the Ah and same chemistry.

Thanks

[d8veh]

It's easier to start with a higher voltage battery, then you get more speed throughout the discharge range of the battery. If you have a 48v one (13s), get a 52v one (14s).

[cooking monkey]

Don't do it. You'll only be tempted to run your main pack down to its low-voltage cutoff, which is abusive to it.

If your pack is 13S (48V nominal), then you can add a 1S supplementary pack of the same capacity (16Ah) for the entire discharge-- not just the end of the main pack's discharge. If your pack is 14S (52V nominal), well, enjoy it the way it is. Your controller would probably be harmed by 15S fully charged voltage.

I did it but am taking your advice and running the supplementary pack with the main pack at all times. I also have a voltmeter added to the main pack so I am always aware of its voltage level. So far its been working fine.

[markz]

Loco is pretty crazy Ese
As others have said, dont do it.

How crazy am I

[flat tire]

Bad idea.

If you want to go faster and accelerate harder get a better battery, motor, controller and use flux weakening. Then you can have everything except your money.

[dogman dan]

Just carrying a larger battery, will help stiffen your voltage longer into the ride. It might be hard to up the voltage of your bike much without damaging the controller.

But if you add another battery in parallel, your initial voltage remains the same, but it won't drop as fast, and you go farther without losing so much of your speed. It will simply go farther before the voltage drops so much.

[cooking monkey]

Bad idea.

If you want to go faster and accelerate harder get a better battery, motor, controller and use flux weakening. Then you can have everything except your money.

Flat tire, I think I have read every (or most) posts on this board since joining, but I am a infant in my understanding of much that I read, like "flux weakening" Though I will keep reading on and some things will sink in. For the record, I did take the advice of those more experienced, and only run my added pack full time with the main battery so really I now have a true 52 volt battery and now that I have hammered out a few hundred km on it I can say there have been no problems. My added pack is 6 cells in parallel vs the 5p13s of the factory battery. At the same time that I did this I also upgraded the bikes wiring to 10 AWG from what I suspect was lower quality 16 gauge wire. Between the improved wiring and the extra volts, performance has been bumped up. I am now going to move on to another battery mod and place another set of 13 series cells in parallel with the factory pack (just waiting for the battery holders to arrive.), this should lift me to over 20 amp hrs at 52 volts vs how the bike came as 48 volts at 16 amp hrs. I am a complete newbie to e bikes but, This bike as it came is not disappointing, or I should say has not been so to me, I am learning slowly as I go you could say. This may have been my first electric bike but I can say it will not be my last. Since April of this year I am now going north of 2000km on this bike. Little to many of you, but lots to me, I don't think I have even 200 km on any of my non electric bikes, so this bike is really getting me out exercising and enjoying it.