12v batteries in series with two motors

Ay! No!

Wiring them up like that will just make the batteries short out across each other!

What you want to do hook up the batteries in series (battery 1 (+) goes to battery 2 (-)) and then hook the motors up in parallel (connect both motor (+) to battery 2 (+) and both motor (-) to battery 1 (-)).

There's still something not quite right. Study this over & then resubmit your sketch?

Yah, according to your newest sketch, the batts will still be shorting out through each other. Same with the PV cells.

Also, it's not a good idea to just attach PV cells directly to the battery. While it won't to any harm to the cells, the batteries could get overcharged, or even not charge at all. What you need to do is run them through a battery charger. The switching chargers (no transformer; lighter weight) should work on DC.

Yah, according to your newest sketch, the batts will still be shorting out through each other.

I don't see any shorts. This is the way I have been connecting batteries for... well lets just say a long time.

Here is my old diagram, looks the same to me.
Frxdy, looks to me like it is right.

To connect batteries and PVs together you need a device called a "Charge Controller".

Grandpa Chas S.

I've never seen that sort of thing. So it's basically a battery charger that runs directly off of PVs? Neat.

And Frxdy's drawing is fine. It's JY's that's knackered.

Sorry I C
I didn't look at that drawing on photo bucket.

He has the batteries shorted big time and the motors will not run. The only thing that will happen is the wires will melt. If he were to turn 1 battery around then he would be putting everything in parallel when both switches are on so it would run 2 24-volt motors on 12-volts. Not a good idea, it will just suck the batteries dry in short order.

Grandpa Chas S.

Yeah, same with the PV cells.

Motors are fine, but you don't need that many switches. One on the + side of the batteries and 1 on one of the solar panel poles will be fine.

I was trying to edit my last post as it was in error, check it now. LOL

He needs to line up all the +'s with the +'s and the - with the - and all would be OK with the batteries and PVs.

Grandpa Chas S.

In theory, two motors would be equal to one bigger motor. In reality, it seems that one bigger one is better. Not by much, though. Don't know why.

Potentiometers = terribly inefficient. They were ditched long ago (like 100 years ago) in place of PWM (pulse width modulation). This is akin to flipping a light switch on and off really fast. If you want speed control, use a proper scooter controller. 24V ones are pretty cheap. Less than $30 including shipping.

"I wasn't planning to run a potentiometer, just 50 amp on/off switches. Wouldn't one motor theoretically mean half the top speed at half the amp draw, 22 amps. When I switch on the second motor wouldn't the speed increase significantly, as well as the amp draw double, 44 amps without the potentiometer?
Unless of course the first motor's rpm's were already maxed out and I'm going DOWN a steep hill."

Your current draw is only dependant on the torque needed to move the bike. Say you have one motor going at 2600rpm and drawing 22 amps. If you flip another one on (that's in parallel), then both motors will be going at 2600rpm, but only be drawing 11 amps each.

If you go down a steep hill and the motors are already maxed out, they'll generate enough back EMF to start charging the batteries, actually.

And Chas gave you that link ;).

The real problem with using a switch and no controller is the motor will draw max current when the switch is on. The second motor will do the same. If the batteries are capable of putting out 100 amps the motor will draw 100 amps as soon as the switch is turned on. Motors are dumb they have no way to regulate themselves. Look at it this way, a motor is nothing more than a very long piece of wire. If you take 1000 feet of wire, lay it out in a big circle and connected the ends to a battery you would have a short circuit. Lots of amps would flow through the wire until one of 3 things happened.
1. The wire would get hot enough to melt.
2. The battery would get hot enough to explode.
3. The battery would discharge rapidly to 0-volts and be worthless.

The current flow would be the same if you connected a second 1000 foot wire adding nothing to the power equation. In other words a second motor in this configuration would do nothing to help the first motor.

Another item I think you need to know is "Current (amps) equals torque", "Voltage equals RPM". Adding more amps to the motor will not make it turn any faster. This just makes it get to top speed quicker. Adding voltage will make the motor turn faster or give you more RPM.

If you take a 24-volt motor that runs at 2600 RPM and add another 12-volts to it so it is now running at 36-voltage the RPM of the motor will increase to something around 3800 RPM. This is know as over volting the motor, I am sure you have seen that term here on V in other posts.

I have one e-bike which uses a 24-volt motor. I replaced the controller with a 36-volt controller and added another 12-volt battery to my pack. With the 24-volt battery pack and controller @ 26 amps the bike would top out at around 18 MPH, with the 36-volt battery pack and controller also at 26 amps the bike tops out at 23 MPH. I have over 300 miles on the 36-volt conversion and the motor is still running great. If I did not have a controller on this bike the motor would draw over 100 amps and get to 23 MPH very fast, if the motor did not toast in the first 8 seconds, then the motor would let go it's magic smoke and the ride would be over.

Grandpa Chas S.

I own a little scooter. It has a 250 watt 24V motor from the factory. It went 12 MPH. I had a second identicle scooter.I removed it's motor and battery pack and made the scooter a two wheel drive. It now goes 22 MPH and has way over twice the range. Yes, 22 MPH is a bit scary!

It now goes 22 MPH and has way over twice the range.

I can see why it would go faster because you now have 500-watts doing the work that was previously done by 250-watts.

I can also understand why you have more range. Before you were running 1 24-volt pack and now you are running 2 24-volt packs. This just doubled your amp hour (AH) rating. More AH equals more range.

All of this is consistence with the laws of electronics.

Grandpa Chas S.

"Will the motor only draw what it needs to move the bike or will the motor just use all available amps that the batteries can give it once I flip the switch to move the bike AND then the load taper off once the bike is moving?"

Yeah, it'll draw a lot of current momentarily to accelerate and then taper off as you approach your top speed. They're relatively small motors, so you might not have a problem unless you are flipping the switches on and off a lot. A controller limits the current to a set value, so you never draw more than what it's programmed for.

"I've been looking at a few PWMs, they have alot of wires for motor, throttle, battery, brakes."

And that's just a basic one. I have one for a skateboard that has connectors for the battery, motor, throttle, brakes, key, two lights, and charger.

"Will I need two controllers and two throttles since I am running two motors? Or do you guys think I should give up on the two independently switched motor idea and just wire them together in parallel so the both come on (and go off) together? Either waysince my motors are 24v/350w/22a can I use one 24v/350w controller or two of them, OR perhaps find a 24v/700w controller?"

No. One suitably sized controller will be fine. If you use a controller, there's really no point to having switches on the motors. Turning one off won't affect the performance much; it will just push the motor harder. A 24V 350W controller will limit the current to around 20A, so you'll need a bigger one to run them in parallel. There aren't that many controllers that are 24V 40A, though, because most systems of over 400W or so run off 36V. Less resistive losses that way.

Will the motor only draw what it needs to move the bike or will the motor just use all available amps that the batteries can give it once I flip the switch to move the bike AND then the load taper off once the bike is moving?

Yeah, it'll draw a lot of current momentarily to accelerate and then taper off as you approach your top speed. They're relatively small motors, so you might not have a problem unless you are flipping the switches on and off a lot. A controller limits the current to a set value, so you never draw more than what it's programmed for.

What LinkOfHyrule said is correct what he did not say is the motor will draw the max amps the batteries can put out. So if your batteries can put ot 100 amps that is what the motors will draw. With a 350-watt motor something will smoke. I would use a PWM controller and the motors in parallel. Most lead acid batteries can deliver well above 100 amps.

Grandpa Chas S.

[/quote]
what he did not say is the motor will draw the max amps the batteries can put out. So if your batteries can put ot 100 amps that is what the motors will draw. With a 350-watt motor something will smoke. [/quote]

I don't believe so.... if the motor is a 350 watt motor, it will draw 350 watts. Think of a light bulb that draws 15 watts. Just because the batteries can put out 100 amps, the bulb will not blow, it will just draw what it's rated for.

Not necessarily. The motors are RATED at 350W continuous, but will draw much more power if suddenly given a power source.

However: The will not draw whatever the batteries can put out for any appreciable amount of time. True, at stall they will draw a significant current, but assuming they are not undersized for the load (or at least geared for plenty of torque), they will only do this for a small amount of time.

I've seen a few cheap (or experimental) scooters (and one go-kart) that simply used a few batteries and an array of relays to switch voltage levels. Obviously, they lacked fine speed control, but they worked, and the motors handled the load fine (even when overvolted).

But, it doesn't really matter if you decide to use a controller. Then it's not so much what the motor can take as it is what the FETs can take.

OK, lets look at some simple electronics.

What is the resistance of a 100 watt light bulb?
(E*E)/P=R
(120*120)/100=144 ohms

OK 144 OHMS of resistance in a 100 watt light bulb.

How much resistance is there in a motor? less then 1 ohm, here is the explination.
When power is first applied to a motor, the armature does not rotate. At that instant the counter-emf (resistance) is zero and the only factor limiting the armature current, is the armature resistance. Usually the armature resistance of a motor is less than one ohm; therefore the current through the armature would be very large when the power is applied. This current can make an excessive voltage drop affecting other equipment in the circuit and even trip overload protective devices. As the motor spins faster the resistance of the motor increases and the current through the motor will decrease.

So if we assume 1 ohm of resistance and use the formula; I=E/R at 24-volts the current draw will be 24-amps but we know the resistance is less then 1 ohm. If the resistance is .5 ohms the current is now 48-amps using 24-volts. If the resistance is .3 ohms the current is now 80-amps using 24-volts. Now you can see how fast the current flow can increase. If we choose .1 ohms at 24-volts which is about as close to the start of the motor as we can get the current flow would be 240 amps assuming the battery could produce that much, get the picture? Remember a motor is nothing but a long piece of wire. If you take a long piece of wire the resistance is very low and the wire will flow loads of current if there is nothing in the circuits to give resistance to the current flow.

Grandpa Chas S.

OK I like to take things one at a time. Makes it simpler.

1. You don't need the switch between the batteries and the charge controller. This connection does not need to be switched. Allow the solar panels to give you all the power they can even when riding. The charge controller will maintain the batteries for you.

2. The motors you have chosen are brushed motors so no problems there.

3. The 2 "SC" (PWM controllers) each have their own throttle. How do you plan to control the motors? One throttle with each hand?

Grandpa Chas S.

I think that answers one of my questions. One (48 volt) throttle cant be spliced to control two 24 volt PWM speed controllers?

short answer - NO!
Why? The throttle is the same for most controllers. It is either a Hall effect sensor or a 5K ohm pot (potentiometer/ variable resistor). This is a simple device which normally uses 3 wires to tell the controller how much power to send to the motor. Throttles normally have 3 wires, one wire is normally +5-volts dc, The other is 0-volts dc, and the last wire is the control wire and varies between 0 and 5 volts dc. This of course is stated in general terms and actual voltages may vary some for controller to controller but by less than 1 volt.

Perhaps lining them up side by side since they are so small with a removable bracket across both thumb levers so they both move together when I want them to? I have really big thumbs (and feet). Grow another thumb on one hand? Smiling Use two hands? I like the idea of controlling them individually still.

That is a mechanical solution that might work but not very elegant. You could take the ground wires and the control wires from each controller and wire them to 1 throttle. Wire the +5 volt wire from only 1 controller leaving the other controller's +5 wire not connected. The only other thing you need to do to make this work correctly is to place a wire from the negative side of one battery pack to the negative side of the other battery pack so ground is the same for both controllers.

I cant let go of the idea that only using a 1000' wire "will" save battery power over a 2000' wire. I believe you, and I'm trying to let that one go, but its hard. I use dual carbs on my race engine, It should be the same, It should. It should. It should. It should. Sorry, I digressed.

OK we go back to simple electronics. When you calculate 2 resistors in parallel use the following formula . So 1000 feet of wire has a resistance of x, for ease of calculations we will say x=1000. You do not add the 2 motors together, that would be series. The configuration you are using is parallel. So if x = 1000 then
1000 * 1000= 1000000
1000 + 1000 = 2000
1000000 / 2000 = 500
So as you can see the total resistance does not add but in fact in this case is cut in half. Back to the other formulas.
I = E / R so if we look at the current flow for 1000 ohms at 24 volts we get 24/1000=.024 amps
I = E / R so if we look at the current flow for 500 ohms at 24 volts we get 24/500=.048 amps
This shows, as the resistance decreases the current increases proportionately. Yes dual carbs uses twice the fuel and so do dual motors. You just have to use the correct formula to see it.

Grandpa Chas S. (A.K.A Mr. Wizard)

Two thumb throttles side by side. They work on my stand up scooter. I think it might get uncomfortable after a while on a bike. I added a rubber stubby on the outside one to make them line up properly.

Free Willey...

Ride on Shamo...

Sorry I don't know what came over me. I think this will work but you better have a really big thumb.

Grandpa Chas S.

Ay, that's a monster of a throttle! LOL, what's with the orca "hood ornament"?

IMO, tying the throttle wires together would be the best way to go.

This should be self explanatory but if you have questions please ask. Remember there are no dumb questions only dumb answers. I thought you might like this because it gives you the ability to disable one motor and only use it when you need the extra boost. Of course the easier way is just to turn the key switch off for one controller which also disables one motor.

Please note - The diagram shows the green wire switched to the red wire. This is correct for some controllers but not all. If this does not work then place the switch between the green wire to the black wire and the controller will be disabled. The easy way to find which way to wire this setup is to take a voltage reading across the green and black wires when the throttle is in the off position. If the voltage is near +5 - vdc then place the switch on the red and green wires. If the voltage is 0 - vdc then place the switch on the black and green wires. (Wire colors may vary but the principal is the same)

Grandpa Chas S.