Old Giant struggles with hill.

[jarnold]

Eventually got the new (Brainpower) controller shoehorned into this very old Giant Twist Express. Fitted a PAS to the crank, as the torque sensor on the rear dropout needs a bit of voltage shifting/remapping to work with the throttle input, and I can't be bothered to do anything until such time as I think the bike's viable. Everything works OK, except that it really struggles to get my 185lbs up the nearest hill. Which is a shame, because the only reason I acquired it is that I'd like to get some cycling in for exercise, having had a triple CABG a couple of years ago, but live in a very hilly area. The batteries are only 24V, but I tested them with a 24v 100w light bulb, and they both seem to have about 80% of the rated 9Ah capacity. The display(S866) shows in excess of 300w at times, although there is a bit of voltage droop(that's normal, isn't it?).
Would it be worth me trying a 36V battery, or would I fry the motor?

 

[thelarkbox]

II certainly require more than 300w of assistance climbing hills,,

To employ a 36v motor you would also require a controller able to handle a 36v supply you would fry a 24v controller before the motor suffered any ill effects..

afaik excess heat would be your major concern 'overvolting' the motor, so if you just apply caution and check the motor temperature often after you first upgrade (touch the hub and see if its HOT) you should be able to gauge the danger fairly accurately ie if the motor remains cool to the touch ride on.. and if it gets hot at the top of long hill BUt your coasting down the other side for 10 mins after ride on.. But if it fails the 'will it light a match by touch' test half way up 'steep hill #2' - yeah not so good..

 

[jarnold]

II certainly require more than 300w of assistance climbing hills,,

To employ a 36v motor you would also require a controller able to handle a 36v supply you would fry a 24v controller before the motor suffered any ill effects..

afaik excess heat would be your major concern 'overvolting' the motor, so if you just apply caution and check the motor temperature often after you first upgrade (touch the hub and see if its HOT) you should be able to gauge the danger fairly accurately ie if the motor remains cool to the touch ride on.. and if it gets hot at the top of long hill BUt your coasting down the other side for 10 mins after ride on.. But if it fails the 'will it light a match by touch' test half way up 'steep hill #2' - yeah not so good..

Thanks, the controller is rated for 36v.

 

[saneagle]

Eventually got the new (Brainpower) controller shoehorned into this very old Giant Twist Express. Fitted a PAS to the crank, as the torque sensor on the rear dropout needs a bit of voltage shifting/remapping to work with the throttle input, and I can't be bothered to do anything until such time as I think the bike's viable. Everything works OK, except that it really struggles to get my 185lbs up the nearest hill. Which is a shame, because the only reason I acquired it is that I'd like to get some cycling in for exercise, having had a triple CABG a couple of years ago, but live in a very hilly area. The batteries are only 24V, but I tested them with a 24v 100w light bulb, and they both seem to have about 80% of the rated 9Ah capacity. The display(S866) shows in excess of 300w at times, although there is a bit of voltage droop(that's normal, isn't it?).
Would it be worth me trying a 36V battery, or would I fry the motor?

36v would help a lot. All the 24v controllers I tried at 36v worked OK, but I can't guarantee that it won't blow. If you want to be more sure, open the controller and look at the big capacitor in it. If it has a voltage rating over 42v, it should be OK, most are 53v or more. That's the thing that blows when you over-volt a controller, and it only blows if you exceed it's voltage rating that's written on it. If it does blow, there's often a loud bang and lots of pungent smoke, but it's not really anything to worry about other than don't breathe the fumes. The same happens when you connect a battery the wrong way round.

The main problem when you run a 24v controller at 36v is that the battery indicator lights/display will always show full and the controller won't cut-off when your battery is empty. Considering the low cost of the controllers compared with a battery, you might as well replace both with 36v ones. I've done that several times on 24v bikes, and all the owners were very pleased with the results.

Your motor can handle a lot more power. You can go comfortable up to 17 amps, which would give you all the power you need. I'd recommend a KT controller if you can afford it. they're about £80 with the LCD, so about double the price of a Brainpower, but they work a lot better. The Brainpower at 36v will give full power every time you startup, no matter what assist level you're on, which can be a bit uncomfortable and wasteful. The KT gives a different level of power on each assist level, so you can make it nice and gentle when you want.

 

[jarnold]

Thanks. The controller is 24/36/48V, and has a settable parameter for nominal battery voltage, and another for low battery level, so I'm not really worried about that, I was more worried about the motor.
So now I need to concoct some Heath Robinson way of temporarily applying 36V to see how it works, before throwing more money down the drain...

 

[saneagle]

Thanks. The controller is 24/36/48V, and has a settable parameter for nominal battery voltage, and another for low battery level, so I'm not really worried about that, I was more worried about the motor.
So now I need to concoct some Heath Robinson way of temporarily applying 36V to see how it works, before throwing more money down the drain...

It'll work. No need to test anything.