learn as you go

Stubby79 · #31 (**permalink**) 07-18-2009, 05:27 PM

Is that 14 gauge solid wire (the kind you put in the walls of your house) or normal (flexible) wire? Low voltage electricity doesn't work well with solid-core wire; it's the same effect as running a noticeably smaller gauge wire. I wouldn't have even thought you might be using household wire if you hadn't mentioned using a light switch as your power switch. For similar reasons, I would think the switch isn't going to be the most efficient, either.

In theory, you're pulling about 15 amps (350w / 24v = 14.583a). Depending on how long the wire is, I'd recommend 12 or better yet, 10 gauge automotive-type(or something similar) wire. The longer the wire, the bigger it should be, so if your switch is at your handlebars and your motor and batteries are at the back of the bike, go for the 10 gauge. Better yet, use an automotive relay, so the wire between the batteries and the motor is only inches long, and use a remote switch to turn the relay on and off. That would be the most efficient way of doing it. You could use a tiny/discreet wire running to the switch then, if aesthetics matter.

There are reasons behind my recommendations(no, really, there is!). Efficiency being one of them. Drawing more current than a given wire can comfortable handle will make the wire hot, and said heat is wasted electricity. The other being that your motor won't get the power it's demanding (especially under load) - the voltage at the motor will be less and therefore so will the amps. Your motor now has to work harder than it should, running less efficiently and wasting more power as heat. More pwoer as heat makes your motor burn out much sooner.

Well, that's the first half of my lecture on electric basics done, now to throw chemistry into the mix. For all I know, I'm wasting my breath and just annoying you and everyone else, so feel free to tell me to shut up if I'm not providing any useful information.

So...batteries. You're running 2x7.5amp-hour, 12-volt batteries. And pulling up to 15 amps out of them. So, in theory, at full draw, they should last half an hour...but they won't last half an hour under that load. They'll last 15 minutes, most likely. The faster you draw said amps out of the battery (lead-acid/SLA at least), the fewer amp-hours you actually get. In other words, the greater the draw, the less efficient the batteries. It's also hard on the batteries, draining them too fast, and they will have a much shorter life span.

In other words, I think the batteries are rather undersized for the job. Not so much because you need twice as many amp-hours but more because you're losing half of said amp-hours to the inefficiency of the batteries. Larger batteries can put out more amps with less efficiency loss. If you switch to 12 amp-hour batteries, you won't get 1.6 times as much range, you'll probably get 2 times or even more. The next size up from that would be optimal, they come in 15/18/20 amp-hour, depending on the manufacturer/quality. And rather than 2 to 2.7 times as far as your current batteries take you, you'd be looking at more like 3 to 4 times the range. And the batteries would have a much longer life span too. Or a second bank of 7.5ah batteries in parallel would have the same effect. (aiming for the batteries to last 1 to 2 hours under full load is an easy way to decide what size batteries to go for)

Sheesh. That was a long way of pointing out that your wiring might be inefficient, and that your batteries are (almost certainly) undersized for the job. I'll shut up now.

deacon · #32 (**permalink**) 07-18-2009, 06:52 PM

No I always appreciate the advice. I live in a town called High Point North Carolina. The reason is that its on the west side of the Piedmont plateau. Lots of up and down hill. The bike coasts a lot of that two miles I was talking about.

Wiring: the wire is 14 gauge multi strand wire, heavy duty Lamp cord actually. It only overheated when I ran the motor without a fuse or controller. It might be too small so I'll keep an eye on it. The switch I use is not the 15amp but the twenty amp one. The kind used in heavy duty circuits. I tried the 15amp but they had a tendency to melt together lol... Remember the title of the thread 'learn as you go'. I have been a while now, long enough to have had most of the things you mention happen thereby teaching me the hard way. Not that I don't appreciate the advice I really do.

The seven amp hour batteries were bought to supplement my 12ah batteries to extend the range some in a parallel application. I found that they will hold up for the two mile ride to the park. They may die early as you suggested. I will keep an eye on them.

I do run 12ah on my 500 watt pusher bike. I will also be running them on the hub motor it I can make it work. I have the batteries sitting on the charging table now.

The bike with the 7ah batteries is a small lightweight bike actually a twenty inch bike frame with the 16" pusher trailer. The biggest problem with it right now is that the coaster rear wheel lacks the gearing to allow for early pedal pickup. If I could pick up the pedal earlier on the hills I could take a lot of strain off the motor I think. I have a twenty inch geared rear wheel I will have to consider putting back on there.

Again please feel free to give me any advice you have. I can use all the help I can get. If nothing else I will be prepared when things go wrong.

deacon · #33 (**permalink**) 07-19-2009, 01:59 PM

Today's experiment was to run the same bike with a 500 watt motor on 24volts and 36volts. Of course there was a difference but how much. It was noticeable for sure but it wasn't enough for me to leave the bike at 36v. Why you ask? because the extra pedaling I did was minimal and very easy to do. In other words, "She weren't no trouble atall."

What I did was to mix and match my batteries. I put two 7ah 12 v and one 12v 12ah battery on the bike. I can configure them either or 24v or 36v with no trouble at all. I figure that is the best of both worlds. If I find a place that I really need 36v I will consider setting it up for 36v... If not I'll leave the 7ah in parallel for the extra range.

Where I do need the 36v is on the 250 watt hub motor. On some of the long hills here I get winded. That should help with it. The new 36v controller should be here this week I hope. I have already put the wheel back on the bike and added a new throttle, I also have the battery trailer finished. I am going to add a lid to it so that I can put a basket on top to carry things. You can never have too much storage space on a bike.

deacon · #34 (**permalink**) 07-20-2009, 08:12 AM

I was having so much trouble with the 350watt on the small bike that I had to park it and go with the 500 watt on the 24" bike today. It works so much better on the ride to the park. I can run the 350 at 36volts on a bigger bike and get pretty close to the same performance. I don't need to do that just now but at least I'm pretty sure I can. I won't have to buy a different setup if the 24" dies. I can just replace components from the smaller bike.

I will soon hopefully have the hub motor up and going as my second bike. I like having a lower power bike as well as the 500 watt pusher. I think pretty much as I did before that a 600 watt 24 or 36 volt hub motor would be a good all around bike. I would personally rather have brushes. I'm not sure that I could find a brushed hub motor these days.

Stubby79 · #35 (**permalink**) 07-20-2009, 08:24 AM

Is that 350 watt motor that you were running at 36 volts originally a 24 volt motor? and if so were yo using a speed controller of some kind?

deacon · #36 (**permalink**) 07-20-2009, 11:42 AM

At the moment I'm not running it at all. I have run my 500 watt at 36 volts with a 24v heavy duty controller from tnc. I just ran it a couple of miles then put it back to 24v.

The 350 I am going to run at 36 next. I am running a cheapo 24v controller on it but I expect it to blow. When it does, I will go with a 36v from tnc. I think I am going to get the 800watt so I can use it on even larger motors should one show up. Things change often in my building.

deacon · #37 (**permalink**) 07-20-2009, 05:24 PM

make sure you know where your reading glass fell before moving the bike being worked on. I just ran over yet another pair. It's a darn good think I know where to get them cheap.

deacon · #38 (**permalink**) 07-20-2009, 09:23 PM

Since I had some time today, I began to rebuild the 350watt pusher. What I did was make a complete unit of the motor and drive wheel. I cut the rails down and made cross bars at the front and rear of the wheel. I also mounted a sorta harp on the bicycle. I have to attach the two pieces together tomorrow. I think it will give me a more secure mount. If it does I will be converting the 500 watt as well. If not it was a good try and I'll just keep trying things till something works.

deacon · #39 (**permalink**) 07-21-2009, 09:09 PM

I have had four different posts get lost today... I wonder what is going on...

deacon · #40 (**permalink**) 07-22-2009, 09:48 AM

Okay today I did a sort of almost scientific experiment. I used one 12v 12ah battery plus two 12v 7ah batteries in parallel to make a 24v circuit. I rode the bike about 2 miles more or less then read the battery voltage on each of the three batteries.

first the results... 12v 12ah =12.4 volts................. 12v 7ah 12.9 volts each............

I was more than a little surprised by the difference. I expected it to be a couple of tenths of a volt difference but not that much. all of them started at 13.25v before I left home I did read them to be sure.

Now I realize that I made a 14ah battery with the parallel circuit but still I wouldn't have expected that much difference. It doesn't look like much but percentage wise it is a lot.