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Child Item

Transformers

Thunderbird2

Can I connect two DC transformers together to give me more amperage ?
I'm looking to connect a 12v 2amp trafo with a 12v 3 amp trafo to power a drill motor .
The motor works with a 6v 3.8ah battery
But barely moves with a 12v 3 or 2 amp transformer

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Gurgle

You could, so long as you include diodes to prevent one transformer feeding back into the other.

What current does your motor draw at 6V?
3.8Ah is the battery capacity, it doesn't tell us anything about how much instantaneous current it can supply.

Thunderbird2

I couldn't tell you

The problem is the battery not lasting long enough . It's for a halloween prop so the motor is only operational for 5 secs. Every time a pir is tripped .

Thunderbird2

These are the only specs I can find

Gurgle

You can pair them (with diodes) and you'll get a max of 5A at 12V.
This gives you 60W of power.

Attached pic shows where to put the diodes. Make sure to get ones that can handle 3A.

You could try it without the diodes. It may work, or the weaker supply may turn into a twisted smoking ruin.

2011

Thunderbird2 wrote: »

Can I connect two DC transformers together to give me more amperage ?

I hate to be pedantic, but transformers are AC and should have the same output if they are to be paralleled.

Gurgle

2011 wrote: »

I hate to be pedantic, but transformers are AC and should have the same output if they are to be paralleled.

In this case we're talking about 'Mains powered DC supplies', not simple transformers.

Thunderbird2

Do they not give out DC ?
So will the above method not work ?

Thunderbird2

AC in DC or AC out ?..?

Thunderbird2

So if I have two 12v 3 amp transformers I won't need to go pull diodes from the TV in the shed ??

Gurgle

A transformer takes AC in and gives AC out.
These power supplies contain transformers and rectifiers. AC in DC out.

Gurgle

Thunderbird2 wrote: »

So if I have two 12v 3 amp transformers I won't need to go pull diodes from the TV in the shed ??

This still applies:
"You could try it without the diodes. It may work, or the weaker supply may turn into a twisted smoking ruin."

The supplies probably have diodes built in anyway....

Thunderbird2

Sure il give it a shot anyway :-)
Il pop it open first and have a look in

2011

Gurgle wrote: »

In this case we're talking about 'Mains powered DC supplies', not simple transformers.

Agreed.

230VAC in and 12VDC out.

As you said suitably rated diodes would be best to prevent one unit from feeding the other. Ideally both units would be the same size reducing the chances of overloading the smaller PSU.

Thunderbird2

Here's a pic of the two . why won't one of these power the motor when a 6v 3.8ah battery can ?

Gurgle

Simplified calculations:

Thunderbird2 wrote: »

why won't one of these power the motor when a 6v 3.8ah battery can ?

The 3A supply can provide a max current of 3A at 12V, max power output is 36W.

Thunderbird2 wrote:

The problem is the battery not lasting long enough

3.8Ah = 228 Amp minutes
If the battery lasts for 10 minutes, then its drawing 22.8 Amps at 6V = 136W
If the battery lasts for 5 minutes, its drawing 272W

2011

Thunderbird2 wrote: »

Here's a pic of the two . why won't one of these power the motor when a 6v 3.8ah battery can ?

It is best to start off with the motor requirements.

For this you will need to know:
1) The full load current of the motor.
2) Voltage requirements of the motor (I see you have this)
3) Starting current of the motor to see that the PSUs can deal with this higher current.

As Gurgle has illustrated just because the 3.8Ah battery can power the motor does not mean that the motor has a full load current of 3.8A
This refers to the batteries capacity.

Thunderbird2

It might just be easier to stick to the battery and have it charging when the motor is in the closed position and off I have a charger for it .
The motors power req aren't written on it anywhere. I've tried a 19v 3.42amp PSU and its causing the motor to pulse .
I have a 12 v 7.2AH battery but its too strong

I only have 4k7 resistors but I'm sure they would be able to handle the wattage

2011

Thunderbird2 wrote: »

The motors power req aren't written on it anywhere.

Do you mean current (amps) ?
Do you know what the power output of the motor is (in Watts) ?
If so you can calculate the current.

I have a 12 v 7.2AH battery but its too strong

No it isn't.

This just means that it can supply 12VDC at a given current for about twice as long as the 3.8Ah battery.

Thunderbird2

2011 wrote: »

Do you mean current (amps) ?
Do you know what the power output of the motor is (in Watts) ?
If so you can calculate the current.

No it isn't.

This just means that it can supply 12VDC at a given current for more than twice as long as the 3.8Ah battery.

It's too much power , the motors turning to quickly .
Il only know the info of what's in the link

Thunderbird2

Thanks for all the help guys :-)
I'm ready to give up haha.
Would 1v make a difference when joining the PSUs ? I have a 20v and a 19v

2011

Thunderbird2 wrote: »

It's too much power , the motors turning to quickly .

The smaller battery may be supplying a lower voltage that is more suited to the motor's requirements.
Perhaps the larger battery is in better condition.
If the 7.2 Ah battery is causing your motor problems it is not because it is too large.

If the motors are designed to operate at 12VDC then there is no such thing as a battery that is too large.
A 12V battery a higher Amp Hours rating can simply supply a fixed current for longer than a 12V battery with a smaller Amp Hour rating.

A 3.6 Ah battery can supply 1 amp for 3.6 hours.
A 7.2 Ah battery can supply 1 amp for 7.2 hours.

The current that the motor will draw is fixed and will depend on the resistance that the motor presents to the battery.

For example I have powered intruder alarm panels from car batteries in homes so that they could be alarmed before the ESB supply was connected. By using a larger battery the alarm panel could be maintained for days between charges.

2011

Thunderbird2 wrote: »

Thanks for all the help guys :-)

No bother

I'm ready to give up haha.

Never do that

Would 1v make a difference when joining the PSUs ? I have a 20v and a 19v

It is not ideal, but the diodes should resolve that issue.

Perhaps you should revert to the earlier idea:

Supply the motor from the smaller battery (that suits the motor) and have the battery constantly trickle charging from a charger. This way the battery would absorb the larger starting currents acting like a reservoir. Once the duty cycle is not too high the battery will not drain to the point that it becomes a problem.

It may be possible to use one of the PSUs as a charger, but be warned it may overheat so keep an eye on it and install diodes as described earlier.

Thunderbird2

So can I connect the charger to the battery and from the battery to the motor ?
Is there anyway of lowering the power from the 12v 7.2ah batt ? I found the problem is because the motor is moving a load there is heat being generated on the wire when this battery is connected . The charger is an emergency back up light with the bulbs removed so it has replaceable fuses and diodes :-) . I'm connecting the load on the battery not the light output .

2011

Thunderbird2 wrote: »

So can I connect the charger to the battery and from the battery to the motor ?

Yes, it is worth a try.

Is there anyway of lowering the power from the 12v 7.2ah batt ?

I assume that you mean lower the voltage? Yes you could make a voltage divider out of a few resistors.
It would be a good idea to measure the voltage across the motor terminals when it is connected to each battery first.
Then you will know what voltage the motor "sees" in each case.
That way you will know what the target voltage is (the smaller battery voltage) and what you have (the larger battery voltage).

I found the problem is because the motor is moving a load there is heat being generated on the wire when this battery is connected .

This is a sign that the cable is too small for the current. Use a larger cable and it will not get so hot.

Bruthal

2011 wrote: »

I assume that you mean lower the voltage? Yes you could make a voltage divider out of a few resistors.

I cant see that working too well. A voltage divider with resistors is fine for electronic applications, but likely not great for powering a drill motor. If it is a 14.4 volt drill anyway, the 12v battery will work fine. The motors in drills rotate at very high speed. Between 5 and ten times faster than the chuck which is geared down.

So it may appear as the motor is going too fast, if the motor is being run outside the drill casing.

It would be a good idea to measure the voltage across the motor terminals when it is connected to each battery first.
Then you will know what voltage the motor "sees" in each case.
That way you will know what the target voltage is (the smaller battery voltage) and what you have (the larger battery voltage).

What is that going to tell us?

2011

robbie7730 wrote: »

I cant see that working too well.

It doesn't need to work "too well".
Remember:

It's for a halloween prop so the motor is only operational for 5 secs.

The OP has very little time and I get the impression that this needs to be achieved on a budget.

Bruthal

2011 wrote: »

It doesn't need to work "too well".
Remember:

It's for a halloween prop so the motor is only operational for 5 secs.

The OP has very little time and I get the impression that this needs to be achieved on a budget.

Unless he gets monster resistors, (assuming the correct resistance values), they will burn out instantly. The pwm setup switching a mosfet would be a decent way for that to work from a 12v battery, if 12v is powering it to highly for the application. That could have variable speed.

I seem to be doing a lot of it lately myself. Another childs tractor project starting, the same as 2 years ago. Have to dig out all the drawings I did for the last one:D

The actual voltage being supplied from each battery to the motor.

Apparently:

So I am suggesting that the OP measure the voltage that this battery is supplying (target voltage).

But the OP says:

Now the OP will be able to see what the actual voltage from the battery is.

Its a 14.4v drill I thought. A 12v 3 amp power supply wont power that unless its rated below 30 odd watts. A 6v battery will power it at 25% capacity, and a 12v one at full power and speed.

It is probably just being over powered for the OP`s application, rather than the motor itself being over powered when connected to the 12v battery.

If a 12v transformer setup such as paralleling the 2 transformers, runs it to the requirement of the OP and not at the same level as the 12v battery, this will mean the 12v transformer setup is being overloaded, but is able to power it at a similar level to the 6v battery. The overloaded transformers would show the voltage being pulled well below 12v by the loading.

If a 12v transformer capable of supplying the motor at full capacity was used, the motor will run as if connected to the 12v battery.

If the 6v battery is running it just right, then I suppose a voltage test can show if the battery is maintaining 6v with the motor running, but any proper lead acid, ni-cd, lithium or ni-mh battery will be maintaining its rated voltage while powering this motor.

I guess what you were saying was, test to see what the voltage of the motor was when the OP was happy with its output. But if it is a decent 6v battery, it will read 6v or very close.

Bruthal

2011 wrote: »

Thunderbird2 wrote: »

I have a 12 v 7.2AH battery but its too strong

No it isn't.

This just means that it can supply 12VDC at a given current for about twice as long as the 3.8Ah battery.

Dont forget, the 3.8Ah battery the OP mentions there, is only 6 volt

Thunderbird2

Thanks guys for the help :-) il post pictures of everything . The 12v battery is operating the prop to quickly so il try the trickle charge route on the 6v battery but I can see the fuses blowing . I will place everything outside the house incase anything goes wrong . Tis just for one night :-)

Thunderbird2

The trickle charger worked perfectly !! No wires heating up at all . Thanks a million il post pics and a vid before I take all the stuff down tomorrow :-)