I need a sensor - Help me please!

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kcandteresa
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I need a sensor - Help me please!

I've recently bought a Merida 500 (24v,SLA battery, no mods). The lead/acid battery was worn out so I fitted a lithium ion battery I got from China (just squeezed it in after shaving all the inside mouldings in the battery case). It works intermittently, so I took the plastic fairings off and replaced all the plug and socket connections with soldered joints that I knew to be OK, only thing was the sensor which is taped to the motor is broken. I need a new one but have no idea where I can get one. Can anyone here help? A new one would be ideal, but a second-hand working one would be fine also (just in case someone has a bike which is only good for bits). I live on the Wirral in the UK, but am quite prepared to pay postage from just about anywhere to get a sensor. Hoping to hear from someone soon. KC

amberwolf
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Re: I need a sensor - Help me please!

If it is a hall sensor, go to http://www.digikey.com and type in the number you find on it. Probably it will come up and you can order one. If not, http://www.mouser.com or one of the other electronics places should have them. If you don't see them, get on Mouser's site and start up the "chat" support, and they will help you cross-reference it to one that will work.

--
Michael Elliott
Cybernetic Necromancers, Discorporated
Phoenix, AZ
Watch me build an electric-assisted recumbent bike from recycled junk:
http://electricle.blogspot.com

kcandteresa
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Re: I need a sensor - Help me please!

Amberwolf, thanks for your interest and for taking the time to try to help me. I followed both the links you sent me and particularly the second one seems very useful - there are thousands of sensors there and I will go through them over the weekend. Problem is that there are no numbers on the sensor case or inside - seems like a cheap generic chinese component, plus I have no circuit diagram for the bike's control circuits so I don't know what type of sensor to look for (analogue/digital/voltage range/etc). I think I'm locked in to trying for an original component left gathering dust on a shelf somewhere or one from a broken bike. Maybe if I could find out who in China made the bike and therefor got the sensor? and I'm looking there as well. Merida imported the bike into the UK but no longer have any interest in it and cannot help me. Do you know who imported them into the USA?

amberwolf
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Re: I need a sensor - Help me please!

I doubt anyone that made the bikes or imported them would tell you anything, even if they knew. I *am* surprised there are no markings at all on the component.

The problem is that we don't know what *kind* of sensor it is. It might not be a hall sensor; it could be a thermal sensor. I'd bet on hall just because it is likely a revolutions sensor, for wheel speed. But for that application it could even be a simple reed switch.

I doubt you would be locked into an original part; there are usually at least dozens if not hundreds of options for various kinds of sensors, not including hacks of other types of sensors. ;)

How many wires come from it?

Can you take some good, well-lit photographs of it and post them? If you have nowhere else to host them, Picasa is a free hosting by google;
http://picasaweb.google.com
easy to use (it's what all my bike project blog pictures are hosted at).

--
Michael Elliott
Cybernetic Necromancers, Discorporated
Phoenix, AZ
Watch me build an electric-assisted recumbent bike from recycled junk:
http://electricle.blogspot.com

kcandteresa
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Re: I need a sensor - Help me please!

Hi again, I too am assuming it is some sort of hall sensor (it is strapped to the outside of the motor normally) and it probably does provide rotational speed info, but who really knows?...

I've dismantled the sensor to try repairing it, but it went horribly wrong. Pictures are here:

http://picasaweb.google.co.uk/kcandteresa/BikeSensor?authkey=Gv1sRgCNi6rpSmmamiwAE&feat=directlink

The central land just melted into nothing as soon as my soldering iron touched it when trying to reconnect the red wire. It's obviously just a very thin filem of metal on a substrate. The red wire originally connected nearer the perimeter of the central part. The unit is around 1.25 inches in diameter and 0.5 inches deep. I tried a few searches for the number 2736, but got nothing. There are just the 2 wires connected to it, which go directly to the controller which is totally potted in plastic, so I can't even see where they connect!

If any of what you see makes sense, please let me know.

KC

marylandbob
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Re: I need a sensor - Help me please!

From what I see of the photos, It appears to be a "PIEZOELECTRIC Transducer", or, in otherwords, a device that converts sound/mechanical vibrations/impacts into electricity, or will create a sound/mechanical vibration, if supplied with electricity.--Does the motor work without this device? What does/doesnot operate?--Bob

Robert M. Curry

amberwolf
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Re: I need a sensor - Help me please!

marylandbob is right, is is a "piezo" as commonly referenced. Normally they are used as speakers in things that only need beeps or tones, rather than a regular speaker, especially for things that must endure some weather (as the paper speaker cone would just disintegrate). A ScootNGo scooter horn I have around someplace is made that way.

Based on the way the plastic casing around it appears to be made, it is unlikely they are using it as a sensor. It was probably used as a warning buzzer or beeper, and placed outside the controller case only because the case was potted in plastic. Does one side or both of that casing have a hole or holes in it? (probably the side facing away in the photos) If so, that makes it almost certain it is only an audio output. If that's all it is, then it is not required to operate the unit, though I would definitely leave it on there if possible.

To use it as a sensor would normally require fixing it to the surface it was to detect vibration or flex from fairly securely, and there's no way I can see for that single-mounting-tab plastic case to do that.

Either way, unless they physically break, are bent enough to cause visible distortion, or corrode, piezos generally last practically forever, and I've never destroyed one without being able to see extremely obvious physical damage to it. :) It's unlikely that resoldering the wires to it would hurt anything; as long as they're connected it will still work.

The good news is that if it is being used as a sensor and is defective, you can probably take apart quite a few different kinds of toys to get a new one out, as long as you can get the old one out of the plastic case to reinsert the new one.

All that said, since it is operating only intermittently with the new battery, have you tried it with the old battery again?

There is a good chance that it is the new battery rather than something wrong on the bike if it worked before and does not now.

Another possibility is that the new Li-Ion battery cannot supply the current necessary at some points, where the old SLA battery could. What is the Ah rating of each battery? SLAs can supply much more current safely than Li-Ions of the same Ah rating, though for a much much shorter time. Li-Ions have a BMS or battery management system in them that monitors current draw and voltage drops on each cell. That BMS ensures that no more than the max allowable current is draw, and that the voltage drop across each cell does not go below the minimum allowable to prevent permanent damage.

If the cutting out of power was happening when you were putting more of a load on the bike, like hills, acceleration, then this is the most likely problem.

--
Michael Elliott
Cybernetic Necromancers, Discorporated
Phoenix, AZ
Watch me build an electric-assisted recumbent bike from recycled junk:
http://electricle.blogspot.com

kcandteresa
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Last seen: 9 years 5 months ago
Joined: Wednesday, November 11, 2009 - 09:07
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Re: I need a sensor - Help me please!

Bob and Michael.
Thanks so much for your involvement with this. It seems you are both spot on with your diagnosis, it is just a beeper. After your responses I took it in to a Maplin store over in Liverpool and they confirmed it - even supplied a cheap equivalent! I guess I was just getting too complicated with it. My plan now is to go back to the cabling, recheck all the soldered joints I made and double check everything in the battery compartment - I had to make quite a few alterations to get the LiPo battery to fit in with the BMS board and even so it's as tight as can be (looks like it's going to be a busy weekend!). I'll get back to you next week sometime with the outcome. Thanks again for your help.
KC

tilt2468
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Re: I need a sensor - Help me please!

I just happened along your battery conversation and it may be too late to do you any good, but I was able to expand the battery case on my Merida to hold a larger Lifepo battery from China. Here are related photos: http://picasaweb.google.com/wetzelb/2009MeridaImages# The battery pack extension was made from an ice tray I picked up at Walmart.

The bike has been a pretty good ride so far-- I have about 1200 miles on it. I had to upgrade the rear wheel for the weight (rebuilt with stronger rim and spokes) and replace the chain (snapped after about 1000 miles); but otherwise, it has been a steady performer. I did have to replace the controller, but that was due to my own shorting error when I was adding lights for night riding. I put a large basket on the rear and a small one on a front rack and I use it for a 10 mile commute to work over fairly flat terrain.

tilt

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