The eBike thread

unkel · 30-12-2019 6:32pm

What be all and end all controller would you recommend? Something that I will have forever, LOL!

Joe1919 · 30-12-2019 6:40pm

unkel wrote: »

If current is the issue, I can up the voltage. Just make a different battery and get a different controller (was planning to anyway). How does 72V * 30A sound? Would still give me well over 2kW

I get about 1400w max output power with simulator, Are you taking the efficiency (66% at max power approx in your case ) into account? Keep away from hills and buy replacement planetary gears. (they are cheap).
https://www.ebikes.ca/tools/simulator.html?motor=MXUS_XF07&batt=B7223_AC&cont=cust_30_60_0.03_A&wheel=27.5i&mass=110&grade=0&motor_b=MXUS_XF07&batt_b=B7223_AC&wheel_b=700c&mass_b=130&grade_b=10&cont_b=cust_30_80_0.03_A&hp=50&hp_b=25&k=1&k_b=1&throt_b=100&add=false&blue=Nm&kv_b=7.58

unkel · 30-12-2019 7:36pm

Very interesting calculator. I put in some figures more applicable to me (0W contribution from cyclist

, 29" wheels, total 120kg), your motor and your custom controller. And mutatis mutandis I get:

52V 13Ah downtube - 750W peak, 21km/h at peak power
72V 8Ah downtube - 1400W peak, 39km/h at peak power

Both about 50Nm torque and about 50% efficiency at max power

The figures for max speed at peak power (and higher speeds beyond peak power, when power is on the way down) don't make a lot of sense to me, particularly for the above 52V setup

But the figures do look very favourable for a 72V setup, that's for sure!

SlowBlowin · 30-12-2019 8:22pm

Unkel talking 72 volts !

Madlad has created a monster...

The dog will never keep up.

Joe1919 · 30-12-2019 8:35pm

unkel wrote: »

The figures for max speed at peak power (and higher speeds beyond peak power, when power is on the way down) don't make a lot of sense to me, particularly for the above 52V setup

http://lancet.mit.edu/motors/torquepowerspeed.jpg

Motor power= torque X speed (Rpm).
If you look at a typical power curve, the power is always maximum near the middle (a little higher on ebikes due to action of controller). Its always low at the ends due to low RPM at one end and low torque at higher speed end. The low torque at this high rpm end is caused by the back EMF of the motor that opposes the battery voltage and reduces motor current, thereby reducing power.

One huge problem with trying to get a small motor to run with high power is that the efficiency drops. So, in our earlier example, at 1400w output power at 66%, the battery is suppling 2100w so 700w is being dissipated in the hub and controller. This is a huge amount of heat and is only sustainable for only a short length of time.
One solution is to drill a small hole in your hub and half fill with oil but I dont know how well it works. To be honest, imo, the small hubs can be reliable and efficient and give a good life when used as intended e.g 36v/14amps. I have a bafang with 20,000 km and still running but starting to sound like a milk float now. These motors (depending on winding) are often designed for 36v but will run faster at 48v and more reliably when assisted with a strong pair of legs.

unkel · 30-12-2019 9:51pm

Joe1919 wrote: »

One huge problem with trying to get a small motor to run with high power is that the efficiency drops. So, in our earlier example, at 1400w output power at 66%, the battery is suppling 2100w so 700w is being dissipated in the hub and controller. This is a huge amount of heat and is only sustainable for only a short length of time.

From the figures I put in, it was even worse than that, only about 60% efficiency, so over a kW in heat in the hub and elsewhere. I'd have thought that would be fine for about 20-30s but not to be repeated straight after for sure

Interestingly the efficiency with above 52V battery is less...

Joe1919 · 30-12-2019 11:11pm

unkel wrote: »

From the figures I put in, it was even worse than that, only about 60% efficiency, so over a kW in heat in the hub and elsewhere. I'd have thought that would be fine for about 20-30s but not to be repeated straight after for sure

Interestingly the efficiency with above 52V battery is less...

As more voltage is applied to a motor, it runs faster and more efficient in terms of its power output, as its the current in the coils that causes the motor to heat.. However, as the motor becomes faster on a fixed gear hub, the bike moves faster and the air resistance increases the load exponentially, increasing the current in the motor.
The only time hub motors are on maximum load is when climbing hills or accelerating from start/low speeds momentarily.
But we are looking at this the wrong way around. Lets say you want to travel at 35km/hr and want to compare the two voltages. In this situation, the throttles will be used to back off the power and the results are shown below, with the 52v at 79.8% which is a little more efficient than the 72 volt motor at the same speed.

https://www.ebikes.ca/tools/simulator.html?motor=MXUS_XF07&batt=B7223_AC&cont=cust_30_60_0.03_A&wheel=29i&mass=120&grade=0&motor_b=MXUS_XF07&batt_b=B5216_GA&wheel_b=29i&mass_b=120&grade_b=0&cont_b=cust_30_80_0.03_A&hp=0&hp_b=0&k=1&k_b=1&throt_b=35&add=false&blue=Nm&bopen=true&kv_b=6.33&kv=6.33&throt=24.5

You can try comparing the two motors in different situations e.g a 5% grade, the 72 volt is more efficient but the motor current is a lot higher.
https://www.ebikes.ca/tools/simulator.html?motor=MXUS_XF07&batt=B7223_AC&cont=cust_30_60_0.03_A&wheel=29i&mass=120&grade=5&motor_b=MXUS_XF07&batt_b=B5216_GA&wheel_b=29i&mass_b=120&grade_b=5&cont_b=cust_30_80_0.03_A&hp=0&hp_b=0&k=1&k_b=1&throt_b=100&add=false&blue=Nm&bopen=true&kv_b=6.33&kv=6.33&throt=100

PS.One of the big problem with overvolting motors is that they make the bike run faster, increasing the load (see black load line). So in examples above, increasing speed from legal 25km/hr to 35 km/hr increases motor load from 190 to 436 Watts.

unkel · 30-12-2019 11:19pm

I don't ever have to go over 35-40km/h on the flat, so what's the benefit of having the 72V from your two graphs? None, unless you put in a gradient?

31-12-2019 12:53am

unkel wrote: »

@Mad_Lad - if I should stick to 52V, are these lipo packs good value for money?

Linky

USD 140 for 2, so EUR125 for a 14S 5Ah pack, would need 4 for a 14S 10Ah pack (520Wh nominal) but will get 10% discount for being a first time buyer, that's EUR225 in total

Not cheap given that I have just bought 624Wh nominal of 18650 packs with built in BMS for just EUR100, although I do appreciate the oomph you can get out of these lipo batteries

Well, they won't have the life cycle of LiFeP04 but they can dish out the amps and charging at 5 C is nothing to sniff at either. Having said that my Zippy 8.4 Ah 4 S LiFeP04 I got for my Radios has a 30 C discharge and 5 C chage rate so not bad at all but probably more expensive, was around 90 Euro's for 1 but should last me years and beats lugging around a 12 V 45 AH car battery when I don't need to.

You need cell monitoring for these RC LiPo/LiFePo4 packs, and they have them on the HK site, once you get familiar with it all you won't ever need or want a B<MS again which can fail anyway, then you can learn about bulk charging without balancing because if you use LiPo and don't run it down too low , it won't go out of balance unless some cells are old and/or weaker in general.

What I mean about bulk charging is this, you can get a charger set to the max voltage of your pack which is about say 4.15 volts per cell , leaving a little at the top, so that would be 58. 1 volts hot off the charger if you intended to go with 14S.

I can't say how much power your motor would take but from reading what joe1919 said about your motors weight I would expect not to dump more than 2 Kw into it and that's being easy on the throttle , no mad acceleration so you'd need roughly a 40 amp controller for that with 14S LiPo.

Remember, you can mod your controller by adding a little solder to the current sensing shunt, a tiny bit at a time, but first check the max current the FETs can handle, that will be the peak , above this they will fry. It also has to be capable of dissipating that extra heat, so the controller should have exposure to free flowing air and not be in any form of bag, and that goes for any controller really.

I would say 2 Kw should be a good max to run that motor with not taking it to any big hills, but in Lucan there are no hill so you should be good.

unkel · 31-12-2019 1:03am

What controller would you recommend to me, Mad_Lad, if I want to be able to program it and I want it to be flexible, as in able to run anything from 36V to 72V (or even 90V) and amperage up to say 50A or 60A

In other words, one that will last forever and will do whatever I want it to do

I'd obviously be looking at spending a bit more than the EUR18 I spent on my current controller

31-12-2019 1:29pm

You could try one of the controllers from lyen here, he has a great reputation on endless-sphere.

http://www.lyen.com/

Also check out the cycle analyst , get a controller with the cycle analyst connector and you can adjust speed, current on the fly through the cycle analyst , very convenient.

With the program lead for the controller you can do all that + limit the actual phase current to the motor but it’s great to be able to do all that on the fly.

I don’t think you’ll want to go higher than about 52 volts.

Remember torque arms and good hydraulic brakes , I went with 8 inch disks, the difference in stopping power was amazing and very important, keep an eye on the axle nuts and keep them tight, I would install torque arms , last thing you want is the axle popping out of the dropout when you’re crossing a busy street.

An 8T mac is about the best motor you’ll get for power to weight in any hub motor and will offer the best balance between torque and speed , I could climb pretty decent hills on it no problem at about 40 amps and 52 volts.

unkel · 31-12-2019 5:16pm

Had a great cycle today. Pumped up the tyres of the fat bike a bit more (they were far too low, probably still too low, what's a good cheap digital tyre pressure meter?) and upped the saddle which somehow I had left way too low before. Also parallelled my vruzend 14S3P 5.5Ah battery with 2 Chinese 7S3P 6Ah batteries in series for a 59V fully charged 14S 12Ah battery

That somehow (how?) made a substantial difference. Measured over 1.4kW draw from the battery :eek: during a steepish short climb over the rail way bridge. Then I went to the track beside the grand canal between the Newcastle Road and Hazelhatch. It was rough and mucky. It was brilliant

I was cycling a good bit myself with part throttle but also went full throttle up all the hilly bits and on some in between bits. Motor got hot, but only too hot to touch at the axle end where the motor cable is. How hot is too hot? Batteries and controller just lukewarm, so they are fine. Did almost 10km and battery was still at 54V (3.7V per cell, so about 50% SOC)

The only thing I need now really is a sprung saddle bar for more comfort and to beef up my battery for longer range, although I'm a bit worried about sending nearly 1500W to a 250W motor regularly...

31-12-2019 6:10pm

unkel wrote: »

Had a great cycle today. Pumped up the tyres of the fat bike a bit more (they were far too low, probably still too low, what's a good cheap digital tyre pressure meter?) and upped the saddle which somehow I had left way too low before. Also parallelled my vruzend 14S3P 5.5Ah battery with 2 Chinese 7S3P 6Ah batteries in series for a 59V fully charged 14S 12Ah battery

That somehow (how?) made a substantial difference. Measured over 1.4kW draw from the battery :eek: during a steepish short climb over the rail way bridge. Then I went to the track beside the grand canal between the Newcastle Road and Hazelhatch. It was rough and mucky. It was brilliant

I was cycling a good bit myself with part throttle but also went full throttle up all the hilly bits and on some in between bits. Motor got hot, but only too hot to touch at the axle end where the motor cable is. How hot is too hot? Batteries and controller just lukewarm, so they are fine. Did almost 10km and battery was still at 54V (3.7V per cell, so about 50% SOC)

The only thing I need now really is a sprung saddle bar for more comfort and to beef up my battery for longer range, although I'm a bit worried about sending nearly 1500W to a 250W motor regularly...

Sounds like it could be a bit too much power, might be just about ok with your terrain , but wouldn't take it for hills with that power, I would knock it back to about 700 watts max to be safe unless you don't care if you kill it.

I think 100 Deg C would be a safe max limit, if the axle is hot imagine the stator inside ?

The 250 watt motor would be labelled 200 watts but could be capable of much higher power.

Time for an 8T mac or BBS 02.

unkel · 31-12-2019 6:17pm

Deleted User wrote: »

Time for an 8T mac or BBS 02.

I would have gone an 8T mac motor or equivalent (instead of the cheapo Chinese one I bought) had I realised you could get so much power out of a geared hub motor

This makes a mid motor a redundant option for me

Next step is either:

1. keep going on the fat bike - hope the motor won't die on me as long as I only give it full throttle now and then and no more than about 30s at a time

2. move on from the fat bike (sell it), get a good quality hard tail or full suspension large frame 29er and install the most powerful rear geared hub motor there is

I'll link about batteries and controller after...

unkel · 31-12-2019 6:46pm

Asked on endless-sphere as well

Linky

unkel · 31-12-2019 7:33pm

A candidate:

Nominal 1000W, 48V but can easily do 2kW according to the seller. EUR255 including shipping from the USA

Linky

Joe1919 · 31-12-2019 10:48pm

unkel wrote: »

.......... Also parallelled my vruzend 14S3P 5.5Ah battery with 2 Chinese 7S3P 6Ah batteries in series for a 59V fully charged 14S 12Ah battery.....That somehow (how?) made a substantial difference. Measured over 1.4kW draw from the battery
....

I think its obvious that you are underestimating your battery requirements. Many suppliers recommend 1.5C, i.e The battery capacity should be about two thirds the controller capacity, which would mean 20ah for a 30amp controller. 2C (15ah) (imo)would work for a while but with a shortened life.
Bear in mind that most/many controllers are speed/voltage controlled throttle so will still draw maximum current until motor rpm matches the selected speed.
Finally, it has been argued below that laptop cells are low discharge capacity (half/.5C) and a huge amount are necessary. This makes sense as laptops are not subject to the high intermittent discharge rates that motors are.
https://endless-sphere.com/forums/viewtopic.php?t=45924

01-01-2020 1:54am

unkel wrote: »

A candidate:

Nominal 1000W, 48V but can easily do 2kW according to the seller. EUR255 including shipping from the USA

Linky

I don't think a 10 T would be essential for you because you don't have hills and an 8T has more than enough speed/torque at 52 volts, that would be 50 Kph in a 26 inch rim. Get the high power version or whatever they call it at em3ev can't remember, it's a very long time since I had one.

I was able to climb steep enough hills, 12% and probably a bit more at 40-45 Km/hr with the stock controller supplied with em3ev.

I was running 3.5 Kw into that motor for months and eventually the gears broke but they have higher powered gears now, this is the one to get, the upgraded MAC motor.

The difference with the mid drive is that it can take a lot of power up steep hills because you can change gear to spin the motor faster improving efficiency.

em3ev even supply a temp sensor now which can be hooked up to the cycle analyst which will reduce power if it gets too hot.

My issue with the MAC 8T was the gears not heat, it used to climb hills so fast that it wasn't pulling peak power for long periods. If climbing the Wicklow Hills then you'd want to reduce power but more for battery reasons, a 10T would help here alright, less power would be turned to heat, even a 12 T the difference is that top speed would be a lot slower but you compensate for that by running 72 volts into a 12T.

This will cost u so think about a BBSHD which can do pretty much everything, that included mega steep hills without much issue. If you don't need mega steep hill climbing ability an 8T MAC will do fine and if you go to the steep hills on road just reduce the power and pedal, 500 Watts will make a big difference anyway.

01-01-2020 2:00am

Joe1919 wrote: »

I think its obvious that you are underestimating your battery requirements. Many suppliers recommend 1.5C, i.e The battery capacity should be about two thirds the controller capacity, which would mean 20ah for a 30amp controller. 2C (15ah) (imo)would work for a while but with a shortened life.
Bear in mind that most/many controllers are speed/voltage controlled throttle so will still draw maximum current until motor rpm matches the selected speed.
Finally, it has been argued below that laptop cells are low discharge capacity (half/.5C) and a huge amount are necessary. This makes sense as laptops are not subject to the high intermittent discharge rates that motors are.
https://endless-sphere.com/forums/viewtopic.php?t=45924

This is where RC LiPo comes in , you can size the battery to your requirements, a small pack, even 5 Ah can provice 20-90C of continuous power and up to 10 C charge , this is impossible with most other chemistry, Hobby King have LiFeP04 4S 8.4 An cells but this will be a lot heavier and bulkier but safer, caution required with any chemistry and of course no one should store ebike batteries in the house unattended and at the very least should be left in a fire proof location with a smoke alarm close by regardless of chemistry.

unkel · 02-01-2020 11:38pm

Joe1919 wrote: »

I think its obvious that you are underestimating your battery requirements. Many suppliers recommend 1.5C, i.e The battery capacity should be about two thirds the controller capacity, which would mean 20ah for a 30amp controller. 2C (15ah) (imo)would work for a while but with a shortened life.

It's not so much underestimating battery requirements, more so of pushing my batteries beyond what they should be pushed at. So yes, heading for a shortened life.

I do this on purpose. The 6Ah vruzend pack consists of batteries I all got for free. The other 6Ah pack, consisting of 2 6Ah 29.4V packs, were EUR25 each including shipping. A shop bought good quality 20Ah pack would costs hundreds of euro, the type of money I simply don't want to spend at this stage on batteries.

unkel · 02-01-2020 11:42pm

Anyway, bit of change of plan. Until yesterday, I didn't realise that cycling well away from the public roads, like on canal paths and in public parks, on mountains and in forests, are still considered a public places, which means your bike has to be road legal. Or it can be confiscated and get you in trouble for driving without license / insurance. It can even impact your driving license. Now the chances are fairly small you will get done for this, but I'd rather have a compliant bike or one that can't be distinguished from a compliant bike. So I ordered a pedal assist sensor today.

03-01-2020 12:21am

unkel wrote: »

Anyway, bit of change of plan. Until yesterday, I didn't realise that cycling well away from the public roads, like on canal paths and in public parks, on mountains and in forests, are still considered a public places, which means your bike has to be road legal. Or it can be confiscated and get you in trouble for driving without license / insurance. It can even impact your driving license. Now the chances are fairly small you will get done for this, but I'd rather have a compliant bike or one that can't be distinguished from a compliant bike. So I ordered a pedal assist sensor today.

:rolleyes: I think you'll be grand in fairness once you don't act the idiot.

The courts are a lucrative source of revenue to the state, most people will pay the fine and say nothing but a lot of People don't and really, the Circuit courts don't care too much about non criminal matters such as no NCT, Insurance, Driving an illegally powered scooter lol etc. These are all non criminal matters. Sure you can get points but that's about it.

unkel · 03-01-2020 12:28am

I probably would be grand, but I just don't want to take chances. Same way as I would not drive around in a car with no tax / insurance / NCT.

Joe1919 · 03-01-2020 10:32am

unkel wrote: »

It's not so much underestimating battery requirements, more so of pushing my batteries beyond what they should be pushed at. So yes, heading for a shortened life.

Just be careful in terms of doing permanent damage to cells which kill the cells or worst, can increase the chances of 'thermal runaway' or some other fire risk. But I am really only an 'end user' and no expert. Endless sphere have a separate sub-section on 'Battery Technology' with better info than the ebike section.
https://endless-sphere.com/forums/viewforum.php?f=14

unkel · 03-01-2020 11:10am

Joe1919 wrote: »

Just be careful in terms of doing permanent damage to cells which kill the cells or worst, can increase the chances of 'thermal runaway' or some other fire risk.

Heat wasn't much of an issue in the battery when I pushed it a few days ago. The batteries only felt luke warm. Controller wasn't even luke warm. The heat at the motor was the only cause for worry / future moderation

I guess seeing a peak of 1400W occasionally for a few seconds from a 58V battery means a peak current of 24A. Which with a 12Ah pack is just 2C discharge of the batteries. For sure those 18650s are unlikely to last 1000 cycles that way, but on the other hand that sort of discharge isn't gonna heat up those cells much either.

From this experiment alone I can conclude that there isn't much of a use case for me buying lipo batteries, unless:

1. I want a tiny light weight pack
2. I want significantly more power out of the battery than 1.4kW

03-01-2020 11:23am

Fire is a worst case and Li battery fires are not fun and are very difficult to extinguish, the smoke is also quite toxic they also give off gases. Not pretty.

I know people on other threads, think the e-scooter one feel I am over reacting when it comes to the batteries in e-scooters, ebikes etc and feel they are quite safe , however, Li battery fires can and do happen, certainly , buying from reputable sources helps, the likes of Paul in em3ev , constructs his own batteries to the highest standards and uses proper fuseable links so if a short happens in a cell it doesn't cause a catastrophic failure to the rest of the pack, ebike batteries made by Bosch you can be sure are also built to a very high standard, panasonic built packs etc, it all comes down to you get what you pay for, stay away from junk manufacturers.

No matter how safe People think Li batteries are they need to remember what can happen and the potential fatal consequences and when it comes to my family I never take risks. There's no harm taking simple precautions, simple stuff like don't charge or store near anything flammable, charge on the ( cold ) cooker hob lol , with the extractor fan on etc, charge in the shed with concrete blocks around the battery.

Anyway, I never had issues, never took risks and was well aware of the consequences and never became too comfortable around LiPo.

Just remember that battery manufacturers can and do considerably over rate their batteries. Endless-sphere is full of this evidence or at least was, hopefully things have greatly improved, get recommendations about which LiPo manufacturer to choose over there in the sphere. I'd actually be interested to know who the culprits are these days or are they all gone now or improved.

Endless-Sphere also had some sad stories about house/shed fires.

I abused the crap out of my Zippy LiPo but I knew what I was doing so it was a none issue and it was fun to experiment and LiPo is cheap especially low C stuff for ebike use. Turnigy are better so I would recommend them more.

I have a zippy LiFeP04 for my Radios but I only need just less than 3 C max discharge so that's nothing for the 8.4 ah battery and their charging specs are correct it certainly can take 2 C charge, charging at 15 amps hardly makes it luke warm, that's real fast charging lol.

LiPo is just fantastic for ebike experiments, cheap and extremely powerful you can't get with anything else and can make and configure the pack to the voltage you want, use 30 amp anderson connectors ( the genuine ones ) again, get from reputable source. They act as fuses should you ( and you will ) create a short, I did it several times configuring the pack for bulk charging and balance charging, keep several spares lol, imaging using connectors that didn't vaporize in your hand ? lol no you really don't want to imagine !

I had a 16S 5ah pack that I used to use with my 8T mac when I went out for long cycles, plenty for a 50 Km cycle with plenty of hills as I put in serious effort then had the power for blasts of 3.5 Kw and 60 Km/hr pure fun when I needed. those were the days, I really miss that ebike kit, I'd sell my Bosch haibike in an instant to have that back.

unkel · 03-01-2020 11:40am

Agree that lithium batteries can be dangerous. I charge the ones I built myself and the cheap Chinese packs in the shed. But you have to put things into perspective too. I'd say several billion mobile phones with lithium batteries are charged in buildings every day, a lot of the time in people's bed rooms. And how many fires do they generate? So little, the risk is negligible

But again you're quite right with lesser known battery sources. Wasn't there a scooter battery caught fire in Ireland a few days ago while charging in a house?

Deleted User wrote: »

I had a 16S 5ah pack that I used to use with my 8T mac when I went out for long cycles, plenty for a 50 Km cycle with plenty of hills as I put in serious effort then had the power for blasts of 3.5 Kw and 60 Km/hr pure fun when I needed. those were the days, I really miss that ebike kit, I'd sell my Bosch haibike in an instant to have that back.

Nothing stopping you! That haibike sounds pretty boring yet is probably still worth quite a bit of money. Selling it would finance a more exciting setup

SCOL · 03-01-2020 12:52pm

What's the best option for a commuter bike 45Km round trip to work with a option to recharge in work on the way home there is a good pull up hill for about 10Km. I would like to be able to to 40-50km in places.

I have been using a 2 stroke engine on the bike for years but I think it time to change.

unkel · 03-01-2020 12:57pm

SCOL wrote: »

I have been using a 2 stroke engine on the bike for years but I think it time to change.

On your push bike? Out of interest, have you a motorbike license, and is the bike taxed and insured?

You can establish what you want with a fully legal pedelec (pretty much any of them) with either a large capacity battery, or your willingness to do a good bit of pedaling. Provided you are happy with it doing no more than 25km/h before the motor stops helping

03-01-2020 2:03pm

unkel wrote: »

Agree that lithium batteries can be dangerous. I charge the ones I built myself and the cheap Chinese packs in the shed. But you have to put things into perspective too. I'd say several billion mobile phones with lithium batteries are charged in buildings every day, a lot of the time in people's bed rooms. And how many fires do they generate? So little, the risk is negligible

But again you're quite right with lesser known battery sources. Wasn't there a scooter battery caught fire in Ireland a few days ago while charging in a house?

Nothing stopping you! That haibike sounds pretty boring yet is probably still worth quite a bit of money. Selling it would finance a more exciting setup

I don’t know about the e-scooter battery fire, didn’t hear anything about it.

The risks with li batteries maybe small but the consequences of a fire can be devastating and all for the sake of some simple precautions.

There’s a huge difference between a fire from mobile phone battery and escooter/ ebike which are much larger.

We also may never know how many fires are caused by batteries/ chargers etc.

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