Booster battery advice required

[colonel]

Following all the recent discussions re booster batteries, I have been doing a few experiments of my own. Although very impressed, considering the price, with my scirocco 2 (36v 15ah battery) its maximum restricted speed was only about 14.5mph. Wishing to increase this to approx 18-19mph, and reading the battery boost threads lately, I decided to have a go.

I have a number of small lipo batteries from my other modeling hobbies and so tried connecting a 2200ah 11.4v 3s battery in series with the main battery. As previously suggested by Dv8eh, I added a voltage recorder/alarm via the battery balance connector. This setup gave me18.5mph on throttle alone (high assist setting), and 15.5mph on the middle assist setting. One of the hills on route, normally climbed at 12pmh was achieved at 15mph (throttle only). This test was fairly severe, utilising the throttle much more than normal. My normal riding style gives me 30-40miles over varied terrain on the highest assist setting. The boost battery lasted just under 5miles but was hot to touch, much hotter than when used in one of my helicopters. The battery was an Overlander (Sport)25C constant, 35C peak.

My queries are:

Should my booster battery capacity be greater than the main battery or does it not matter as long as i monitor booster voltage while riding?

De8vh highlighted some hobbyking 4s 5000ah batteries recently, although I have tried 3s successfully would I be pushing my luck with the standard controller, bike equipment,etc at 4S?

Does the booster battery need to have a higher C rating than the 25c experimented with?

I only really want the boost for my 12mile each way commute, other general rides I am happy with the regular 15mph top assist. Therefore, from previous experiments an additional 5000ah would just about do the job. However, would I be better having two batteries in parallel to split the load?

Would the best all round option be to add two 8000ah 3s lipo batteries in parallel to give me 3S at slightly more capacity than the standard bike battery? Each battery fitted with voltage indicator/alarm on handlebars.

Am i likely to do any damage to the standard battery in any of these configurations?

The comments/thoughts of you experienced guys would be appreciated.

 

[Deleted member 4366]

Lots of good questions.
The capacity of the booster battery shouldn't be a problem as long as it can give enough current. It would be intersting to put a wattmeter between the two packs to see exactly what happens, but your booster pack should just be giving 15 amps. How does that compare with it's RC use?

I'm sure a 4S booster pack will be too much. It'll take the voltage as high as 58.8v fully charged , which will almost certainly blow the capacitors in a 36v controller. 3S is right on the limit.

The C rating isn't important. Assuming you go for 10000 0r 15000maH booster, the discharge will be less than 2C.

Be careful about using your present records to calculate required capacity. When you increase the speed, the battery consumption goes up exponentially.

It makes sense to use a pair of 8000maH packs for 11.1v 16aH, then you won't have to worry so much about the lipos running out. You can parallel the balance and power leads so that you only have to charge one thing, and you'll only need one alarm. You can get ready-made leads to do that on Ebay if you don't want to solder them.Make sure that the lipo packs are approximately the same voltage before paralleling them.
3S JST-XH Balance Parallel Wire Adapter to 2 Output 11.1v Lipo Battery Balancer | eBay
deans parallel | eBay

I can't think of any reason the main battery would be damaged, but a wattmeter temporarily between the two will show you what's happening, i.e. whether the lipos are pushing any extra current through the main pack.
New Digital 60V/100A Battery Balance LCD Voltage Power Analyzer Watt Meter | eBay

 

[colonel]

Thanks for the advice Dv8eh.
Can you clarify the issue of the balance cable and a single alarm.
If parallel connected do the two batteries not really consist of 6 cells that should be individually balanced or do they just pair up?
The cable appears to just pair up the two batteries.

I had assumed I would have to charge the batteries individually and have individual alarms to monitor each of the 6cells.

 

[trex]

overvolting with a large capacity booster can kill your bike. The controller low voltage protection does not work, if you drain the main battery before your booster, you can damage your main battery and vice versa. The nylon gear of the SWX motor can also be easily stripped on hills, it's not built to the same robustness of the BPM or CST.
The 8-Fun BBS01 is simplest solution to keep assistance beyond 15mph.

 

[Deleted member 4366]

If parallel connected do the two batteries not really consist of 6 cells that should be individually balanced or do they just pair up?
The cable appears to just pair up the two batteries.

I had assumed I would have to charge the batteries individually and have individual alarms to monitor each of the 6cells.

If you get two lipo packs and join them in parallel, each two (or three or more if you parallel more packs) corresponding cells become one since they have a wire joining the top and another joining the bottom. Everything is joined in parallel, so you can charge them as one. It's only when you connect packs in series that you have to charge and monitor them separately.

 

[KirstinS]

overvolting with a large capacity booster can kill your bike. The controller low voltage protection does not work, if you drain the main battery before your booster, you can damage your main battery and vice versa. The nylon gear of the SWX motor can also be easily stripped on hills, it's not built to the same robustness of the BPM or CST.
The 8-Fun BBS01 is simplest solution to keep assistance beyond 15mph.

That's a fair warning . It can kill your bike

But there is no reason for it to do so particularly as long as you have an understanding of limits of your controller/ motor and take sensible precautions

My main pack is still going after bypassing the BMS nearly 6 months ago. I expected to get a few weeks at best before some cells died (my BMS had failed already BTW)

 

[trex]

There are two limitations when considering derestricting a hub drive bike: maximum no load rotation speed and throttle voltage. The no-load limit is the biggest obstacle.
If you are lucky enough to have a high speed hub motor, fit a sine wave kit with LCD and keep the battery.
If not, the easy solution is crank drive. 36 V crank drive usually tops out about 78 RPM at the chain ring, 48V 106 RPM, the chain ring has 46T. Top assisted speed for the 36V is 24mph, 33mph for the 48V on 12T rear sprocket on 700C wheels.

 

[colonel]

Thanks everyone for all the advice, but it does seem a little varied?

If I upgrade the booster to 2x8000mah that will be larger than the main battery at 15ah.
So as I near battery exhaustion, my main battery BMS will not be able to protect itself?

Would the safer all round solution therefore be to install 2x5/6000mah batteries so these would always deplete before the main battery. Then disconnect them when the booster voltage alarm goes off, continuing on the standard battery if necessary.

I currently utilise a shorted Deans connector to bypass the booster when removed.
A switch would be nice but I guess it would be quite big to carry the current unless a relay was used.
Has anybody got a neat solution to switching the booster or do you all just disconnect?

 

[Deleted member 4366]

The bit about the BMS doesn't sound right. Most BMSs detect low voltage on the cells rather than the total. That feature should always be operating to protect the battery from permanent damage. if you're going to flatten your batteries, you would need to test the BMS protection by running the battery down below what the controller will allow; however, there's a chance that you might have to use special charging procedures to get it going again.

With a booster battery, you lose the controller's protection, and you've no idea how each battery is going down particularly when they fall off a cliff when nearly empty. Ideally, you need a voltmeter on both. If you have one battery with significantly more capacity than the other, then you only have to monitor the smaller one.

The 16aH from the lipos is unlikely to be accurate. Often the actual capacity is less.

If I was doing it, I'd use a wattmeter between the controller and the batteries to show aH consumed, and then after a few runs of increasing length, you should get some idea of how they behave, and you'll get an idea of a safe number of amp-hours to use. I'd keep the lipo alarm on for insurance. As long as you don't go below about 12aH, you should be OK.

 

[colonel]

Im grasping most of that, but no sure why you say don't go below 12ah.
What is the significance of the booster being a lower figure to the standard battery?

 

[Deleted member 4366]

IIUC you want to use 16aH booster with a 15aH main battery. 12aH used should be safe for both of them. Each battery will be giving the same current as the other, so the aH consumed by each will be the same., but that's theory. You need to test that it's correct, to be certain.

 

[colonel]

I will do a bit more experimentation with a 4250mah flight battery I have and check currents to try and determine how the range is affected. Although it would be nice to achieve 24miles range, my commute is only 12miles and I could recharge for the return trip. I am happy with the normal 15mph max and 30-40+mile range for normal recreational use, but just wish to up the commute speed and still arrive fresh.

My current thinking is to go for the 2x6000mah 25c 3s solution as my lipo balanced charger has a max rate for a 6000mah battery! What kind of cost would a new charger be to charge the parallel 2x6000mah lipos and where would be best to purchase one, and advice?

 

[Deleted member 4366]

Normally, lipo chargers have no idea of the capacity of the batteries they're charging. The only thing they see is the voltage. How can it be limited to 6000maH? Are you sure that it's not just the settable safety level so that you don't overcharge small batteries. Even if you can't set it higher, you just press the start button again and it'll do another 6000maH

 

[colonel]

I guess you are right, I wasn't thinking it through. Setting the battery size just sets the safe charge rate, the cut out is voltage driven.

Are the 20C rated batteries adequate for this purpose or am I better going for a higher rating.
I have known some 25C batteries to puff up after a demanding helicopter flight.

 

[Deleted member 4366]

20c will be more than enough. They'll be running around 1C most of the time.

 

[colonel]

Just a quick update for information, should anyone be interested!

To minimise cost on what is just an experiment to improve the bike for my purpose of a 12mile each way commute, I have gone for the following option.

2x5000mah 20c batteries from Hobbyking at £17 each, plus about £15 worth of cables/connectors/lipo alarms, etc. I am still awaiting delivery of a parallel balance cable and a 0-120v waterproof voltmeter.
Without the balance cable I have had to charge the batteries individually and the voltmeter is to record the original master battery on the fly (currently have a small handheld unit strapped to handlebars).

The two batteries fitted into a normal water bottle after a bit of boiling water was applied to "reshape" it (another good reason for the 5000mah size). Batteries now held secure in bottle and bottle good fit in frame. The single connector and balance cable protrude out of the bottle (will silicon seal once finalised) and the bottle is mounted inverted to minimise cable lengths back to the controller area. When not utilising booster pack a simple Deans jumper plug shorts the cable to complete the circuit.

Initial testing:
Without booster, modifications appear to have made no difference to the original 14.5ish top speed on flat.
With booster, achieving 19mph on flat, climbing previous 11ish mph hills at 15mph on high assist.
achieves 15mph on medium assist.

Only had one good flatish test ride so far - 17.5miles at an average 18mph, set on high assist.
lipo Battery usage, start 4.2v/cell finish 3.8v/cell recharged 2425mah (each battery).

I'm hoping this will give me approx 30miles on high assist, ideal for my commute.

Once I take delivery of the remaining items, I will install the voltmeter and lipo meter/alarm properly on the handlebars and then take to the hills. I hope to replicate one of my published "Strava" rides which was about 30miles and 2500ft of climbing on the original standard bike for comparison.

Caught a roadie the other day at traffic lights. He didn't look at my bike as he was too busy complaining about the lights being on red for so long. When they changed to green, he turned and said cherio - his face was a picture as I sped off (fortunately needing to turn left shortly after before he caught me!).

It has been an interesting little project that has given the VFM original bike a bit more of an edge.
Many thanks for all the advice/tips on the way.

Cannot wait for this bike to wear out now, then I can start a new build project..........500w 48V??????????

 

[banbury frank]

Hi What you really need will be one off our Super wings 60 volt 15 AH battery 3,000 watts at the Back Wheel 38 MPH Available in October Cost From £3995 Depending on the Bike we fit To

PS if you already have a Silent wing DONT panic there will be a upgrade Keep you eye on our web site

Frank

 

[colonel]

Very nice i'm sure, but for 38mph and £4k I would be looking at a motorbike!

 

[Scimitar]

Very nice i'm sure, but for 38mph and £4k I would be looking at a motorbike!

Oh, don't worry - it's just Frank never misses a chance to plug something.

 

[KirstinS]

Great result - for a very minimal outlay

There is a lot to be said for the booster battery solution on cheaper bikes/kits