Quick battery question

[Rhinochugger]

I now have a working chassis for the VW Combi Drasine/Speeder (I'll post a picture in the Scratchbuilding section as soon as I've taken one 8| )

I'm intending to use battery power, without any speed control because there isn't a lot of room.

I'm using a 6v motor (from an early Bachmann bug mauler) and have tested the gearbox with two AA cells giving 2.4v. This seems to provide an adequate speed at the axle taking into account the wheel diameter.

However, my intelligent charge will only recocgnise a minimum of 4.8v, and if I use four cells, I'm concerned that the speed will increase.

How can I keep the speed down?

I thought about using two DPST switches instead of a single DPDT to swithc between charging and running. by doing that, I could charge 2 x 2.4 cells in series and run them in parallel :thinking: (NiMh 2100 mAh)

I'd need two in line fuses, but that'll take up less space than a speed controller, and even if I could install a speed controller, there'd be no way of operating it, as I don't want to go to the expense of R/C (I'm supposed to be building this on a budget )

 

[coyote97]

Hi Rhino,


i wont run Accus parallel.
I never understood, why, but they definitely dont like that. Its a question of potential: they always try to have the same potential and therefore having a permanent unload.

Its the same with charging: serial charging works, parallel doesnt.

But to the wiring. The attached plan should work. take a look and give it another test (to look for inidentified shortcuts):

one switch is for changing generally from charging-OFF-driving while the other switch is just for direction: forward-OFF-backward.

Its a bit unusual, but like this u have ALL functions in 2 switches with an inbuilt charging-solution (just need a plug).
Look at the direction-function!
Each direction has its own Battery!

hmmm...maybe not clever for a speeder.....but perhaps its an idea that leads further....


Frank

 

[LTfan]

Agree with Frank - never parallel batteries.
One way to reduce the voltage at the motor would be with a few diodes, in series, between the battery and the motor.
Each diode will drop about 0.7volt; use whatever number give the desired speed.
Something like a 1N5402, widely available. including from Maplin:-
http://www.maplin.co.uk/Module?ModuleNo=19079
Hopefully someone will be along soon who can do a sketch? Is Neil FNR still on here?

Cheers

David

 

[Neil Robinson]

Agree with Frank - never parallel batteries.
One way to reduce the voltage at the motor would be with a few diodes, in series, between the battery and the motor.
Each diode will drop about 0.7volt; use whatever number give the desired speed.
Something like a 1N5402, widely available. including from Maplin:-
http://www.maplin.co.uk/Module?ModuleNo=19079
Hopefully someone will be along soon who can do a sketch? Is Neil FNR still on here?

Cheers

David

Yep, I'm here under my real name.
I'd be tempted to try four series diodes, giving a drop of around 2.8V, in a special charging lead for this vehicle only.
That way there would be no extra power loss or space taken up in what is a fairly small vehicle.
I presume these chargers work by sensing changes in the voltage and/or current. Within reason the diode voltage drop, unlike a resistor, doesn't change with varying current so it should work O.K.

 

[johnsaintjim]

Ian

I would go for the speed controller from and article on GSM which was designed and built by John (can't remember his username nor do I know if he is on here). The speed controller will solve all your charging problems and you will be able to set the speed to whatever you want. I used it on my Bachmann Lyn and it was very effective.

Because it's components rather than a board, I built one using a bit of chocolate block to connect everything. It will fit in a very small space. I have a Word document of the article which I will email you. Components from Rapid were about £15 for enough to build two controllers. The article has all the Rapid part numbers so it's really easy to buy them.

Just a thought.

 

[Rhinochugger]

Oooh, lots of suggestions there, thanks guys, food for thought - I haven't yet ordered the elctrical gizmos.

I needed to check whether the gears/motor/chassis build was going to work first

Now, does anyone produce a sound card for a flat-opposed, air-cooled, under-square, 4-cylinder engine, which backfires at every other lamp post ?

 

[LTfan]

Now, does anyone produce a sound card for a flat-opposed, air-cooled, under-square, 4-cylinder engine, which backfires at every other lamp post ?

Would that be with or without the blowing exhaust?

I'll do a bit of digging-around for some sound effects - I may be some time.

David

Edit - just found this:- http://www.ratwell.com/technical/En...e a sound card that lets you download sounds?

 

[Rhinochugger]

MMmmmm, not sure that I'll have room for sound - but it would be a bit of fun

 

[KleineDicke]

Ian

I would go for the speed controller from and article on GSM which was designed and built by John (can't remember his username nor do I know if he is on here). The speed controller will solve all your charging problems and you will be able to set the speed to whatever you want. I used it on my Bachmann Lyn and it was very effective.

Because it's components rather than a board, I built one using a bit of chocolate block to connect everything. It will fit in a very small space. I have a Word document of the article which I will email you. Components from Rapid were about £15 for enough to build two controllers. The article has all the Rapid part numbers so it's really easy to buy them.

Just a thought.

Here's the speed control circuit- borrowed from Carl Hibbs. Works like a champ. It uses a "Darlington" transistor. The potentiometer should be around 10K ohm, and the other resistor 1K ohm. You can use smaller components and mount them on a small circuit board if you'd like.

and a photo.

 

[Granitechops]

Bill

will that circuit take 24 volts & 3 amps???

 

[Rhinochugger]

Yerst, I was thinking that this would be a good option, but on the plan that I saw, it mentioned the need for a heat sink for the Transistor.

I might be able to do that in some way, but interestingly, this is the layout that Ivan of IP Engineering uses, but it wouldn't control the speed on my 7.2v battery pack when it was installed in the diesel. I ended up using a Cambrian Models controller which has worked well.

 

[Neil Robinson]

In reply to the last two posts, it rather depends on the transistor chosen and what you expect it to do.
Something like a 2N3055 or a TIP3055 should be O.K. for up to 50V, 15A and 80W power dissipation.
It's the power dissipation that dictates the need for a suitable heat sink at higher values.

To work out the power dissipation in Watts simply multiply the voltage dropped in the controller in Volts by the current taken by the motor in amps.

For example if you had a 13.2V battery pack and the motor was running at 12V and 0.5A the transistor would only have to dissipate 1.2 x 0.5, i.e. 0.6W and no heat sink would be needed. If you adjusted the controller to slow the motor down so that there was only 3.2 volts at the motor terminals, again at 0.5A, the transistor would dissipate 5W and get a little warm so a small heat sink may be a good idea, but may still not be strictly be needed.

 

[LTfan]

MMmmmm, not sure that I'll have room for sound - but it would be a bit of fun

Try Googling Campertram - yup, campertram. There's some videos on youtube.
Some genius got two model VW Samba campers, sliced the rear panel off each one, joined them back-to-back, motorised the result and produced a beautiful tram.

That should have plenty of room for sound?

David

 

[KleineDicke]

I currently have two of these controllers built- one with a heat sink and the other without. The one without gets a bit warm to the touch, but doesn't produce any smoke or odd odors, so I suspect the heat sink is good practice, but not strictly necessary when controlling relatively low voltage/low amperage motors. An Neil said, it's all about the watts.

 

[Rhinochugger]

Construction has proceeded - space has decreased

We are still pondering :thinking:

I think it may call for a brief test run on differing numbers of cells, and have to go back to basics.

More news tomorrow nphone:

 

[Rhinochugger]

Brief test this morning.

4 cells = 2 fast
2 cells = 2 slow

Answer, some of the seats are going to have to come out (there goes Jeremy Clarkson again) and we're going for 4 cells, in 2 pairs, with a controller positioned in the middle and the heat sink will be a bit of ally bar under the floor. The controller will be adjusted by test, and then left at a fixed speed. Simple on/off, no reverse.

Charging jack has got to go under the driver's bum.

Looks like that's the battert question sorted, the rest is in Scratchbuilding - when Mr Maplin delivers ( a couple of items are out of stock - like the transistor and the 3mm LEDs for the headlights)