What's my battery voltage - 36v or 48v?

[anachrocomputer]

Couple of points:

If you're measuring the resistance of filament light bulbs, cold, then you'll get a reading that's much too low. When a light bulb is first connected up to a supply, it will draw a large current (according to the resistance you measured), but then the filament will heat up and the resistance will increase. This increase in resistance will make the current fall to the values (Amps) that you measured. Ohm's law has a bit of fine print attached about 'constant temperature'!

And if you've measured the resistance of the mystery component, and it reads 1.44 (k Ohms, presumably) and varies with turning the screw, it's definitely a variable resistor. Also called a 'pot', short for potentiometer. Transistors can come in similar-looking packages, but the never have the adjusting screw.

[badnewswade]

Well, it only has two wires going to the motor so maybe it is a brushed one after all...

How are you going to limit the current drawn from the NiMh battery? The 2Ah 'AA' cells are not really suited to supplying more than 2 amp.

The plan is to use an 18 ohm resistor to restrict current to 2 amps.

Also thinking of putting a resistor on the main battery as well, so that not all its' amps are used and I save power... this will have to wait a while of course, I have to test it with an ammeter which I will do soooon

How are you going to charge them?

For now, just with regular battery chargers. Remember I won't need the range extender on an everyday basis, just once in a while, like if I want to go to Bath or something. I'm sure I'll work something more elegant out long term.

[EVguru]

A resistor just turns current into heat, it's all 'wasted' energy.

[badnewswade]

Actually just realised that a resistor on the main battery would be completely moronic and obliterate the whole point of the excercise which is to make the bike go better.

Got a circuit designed and built and it doesn't not work, sadly I got another £%@&% puncture after only a mile. Got that fixed but also my throttle has fallen off and bike won't be back in action until the new one arrives from EbayLand.

I see what you mean about voltage matching / overvolting a bit now. If I want to actually see any of these amps reflected in the bikes performance I can raise voltage levels with, as you say, an extra couple of batts, otherwise the supplementary power pack will just kick in as the main battery is drained I suppose. Could even install a switch and a pack of two to four extra AAs, so if I want the extra POWER I hit the button and go a little bit faster, if I want the range then I'm a good boy and just leave the thing alone.

Don't think I can make it to this months meet because of it clashing with my book club, but if someone can tell me when December's is going to be I can make a note of it and maybe change the book club's date (lots of them work at weekends and spend time away from town and stuff, so we're always flexible about our own meets).

(Always assuming I don't get yet another £$%!ing flat before then, or something! )

[badnewswade]

Ha! Ha hahahahaha!

Got the bike fixed and built the add-on and plugged it in. Worked fine for a couple of miles then started to peg out. Turns out those "2600 mA" batteries I bought are not 2.6 amps at all, in fact they barely run the bikes lights. At least I haven't damaged my bike and have proved my point (well, kind of)

Moral of the story: Don't buy batts on Ebay!

[EVguru]

I'm starting to sound like a broken record.

BATTERY CAPACITY IS MEASURED IN AMP-HOURS, NOT AMPS!

I'd make it flash too if I could!

Most of us forget from time to time and put A where we mean Ah, but it's important to get it right or it causes confusion.

There is no fixed relationship between the capacity of a cell/battery and it's ability to deliver current. I've seen 1Ah cells that would support a 1000A discharge and 240Ah cells that would only support a 50A discharge. The former were thin film lead-acid whilst the later were Zinc-Air.

Your 2600mAh cells probably cannot support more than about a 2A load without their voltage sagging, so their capacity at a 5.5A (200W on your 36V system) is almost ZERO Ah.

[badnewswade]

Er... I had a resistor in the circuit that limits current drawn to 2 Amp.

Also by way of experiment I tried powering some other items off these batteries. They failed. Also I have some real 2aH batteries from Maplins and they are fatter and heavier, in fact they just about conform to the AA form factor.

I've been ripped off.