Designing my first basic circuit - But have a few Questions

[J0n]

Ok… So I am new to all of this type of stuff. So I may be asking very simple and/or stupid questions but I figured I would ask and get feedback from people who know what they are talking about.

So I have been trying to design a simple(ish) circuit to run two 12V DC motors. BUT I want to run them from a Battery and make it useable via the mains while the battery charges. In addition to this I wanted to add a Battery Indicator (to see the battery charge), a Switch (turn on/off) and a Speed Controller (to adjust the speed on the motors). So I have had a go at drawing it out and wanted to get some feedback on it to see if it would even work…

So the main questions I have our:

- Would this circuit even work?

- Do I need to put in Resistors or something to reduce the Amp’s from the Charger going into the battery’s? Or will the Battery be ok taking 10Amp from the battery?

- Placements of the parts in the circuit? Will the battery indicator just show me the charge of the battery or will it show its fully charged when plugged in?

- Would I be able to do this only using a Positive and Negative wire or do I need an earthing wire?

- Is there anything I am missing/overlooked?

I think that’s everything…

 

[(*steve*)]

There is no need for resistors

The battery is probably 9Ah and will need a charger that supplies far less than 10A.

Other than that your block diagram is basically correct. Normally we would draw it charger, battery, controller, and motor in that order from left to right.

I'm assuming you want to use a lead acid battery. The charge will show higher as you connect the charger. If the charger is not massively too large, the voltage will increase as the battery charges.

 

[J0n]

Thanks for you feed back.

You are correct about the battery being 12V 9Ah. The reason I got a 10A charger was because I wanted to be able to charge and use it at the same time. But Iv been told that its not possible with a basic power supply (http://www.ebay.co.uk/itm/12V-10A-1...187541?hash=item3a87d81155:g:IKMAAOxywXFSbNe3)

So what would you recommend in the way of a charger for a 9Ah battery?

Is there anywhere else in the circuit I could move the battery indicator to give a better read on the battery level?

Thanks
Jon

 

[(*steve*)]

The is no reason that you can't charge the battery while you're using it.

There is no better place to measure the battery voltage than across the battery.

Your load is only 8/100ths of an amp. Ant charger capable of 100mA or more will be able to keep the battery charged even while the motors are running.

 

[J0n]

So... With that being said would the circuit as is (without the resistors) allow the motors to run while the battery is charging?

In addition will the charger (having such a high amount of Amps) damage the battery/make it over heat? & will that change if the charger is only charging the batteries when the motors are switched off?

 

[(*steve*)]

So... With that being said would the circuit as is (without the resistors) allow the motors to run while the battery is charging?

Almost certainly.

In addition will the charger (having such a high amount of Amps) damage the battery/make it over heat?

It's a possibility depending on how large the mismatch is and how dumb the charger is.

will that change if the charger is only charging the batteries when the motors are switched off?

No.

 

[J0n]

It's a possibility depending on how large the mismatch is and how dumb the charger is.

I know i keep asking the same question over and over and over... but im just concerned that the charger (12V 10A) is not suitable for the Battery (12V 9Ah). With or without the 2 motors (12V 40mA) running at the same time. So I guess the main questions are:

Do u think the battery and charger are suitable?
If not can u point me in the right direction of what I might need?

P.S. What do u mean by "how dumb the charger is"?

 

[(*steve*)]

Do u think the battery and charger are suitable

I don't know.

P.S. What do u mean by "how dumb the charger is"?

If the charger is smart enough to realise it is charging a low capacity battery and wind back its charge current then you may be ok.

If the charger is one of the old fashioned barely regulated types then it may very quickly kill the battery.

Post a link to both the battery and the charger.

 

[J0n]

Post a link to both the battery and the charger.

Battery:
http://www.ebay.co.uk/itm/111159905946?_trksid=p2057872.m2749.l2649&ssPageName=STRK:MEBIDX:IT

Charger:
http://www.ebay.co.uk/itm/251387187541?_trksid=p2057872.m2749.l2649&ssPageName=STRK:MEBIDX:IT

Motor (just incase):
https://www.amazon.co.uk/gp/product/B005GNRIM4/ref=oh_aui_detailpage_o02_s00?ie=UTF8&psc=1

 

[davenn]

Battery:
http://www.ebay.co.uk/itm/111159905946?_trksid=p2057872.m2749.l2649&ssPageName=STRK:MEBIDX:IT

Charger:
http://www.ebay.co.uk/itm/251387187541?_trksid=p2057872.m2749.l2649&ssPageName=STRK:MEBIDX:IT

Motor (just incase):
https://www.amazon.co.uk/gp/product/B005GNRIM4/ref=oh_aui_detailpage_o02_s00?ie=UTF8&psc=1

you only need a charger that is around 1 Amp at the most

 

[J0n]

you only need a charger that is around 1 Amp at the most

Yeah... Im starting to get that impression... But im trying to run the circuit to allow the charger to both change the battery and run the motors if i need it to.

 

[(*steve*)]

Yeah... Im starting to get that impression... But im trying to run the circuit to allow the charger to both change the battery and run the motors if i need it to.

But as drawn, the circuit only requires 8/100ths of an amp.

 

[davenn]

But im trying to run the circuit to allow the charger to both change the battery and run the motors if i need it to.

Steve has commented twice about the current requirements

to put it another way to see if it helps you ......

you require 80 mA for the two motors, lets round it up to 100 mA. The controller may use 5 - 10mA, lets say 10 mA

with a 1 A supply you will still be left with 890 mA to charge the battery .... that's much more than what is being drawn from it to run you bits



Dave

 

[J0n]

Well... I feel like an idiot... sorry it took so long for me to understand. But I get it now... well mostly.

Just a couple of follow up questions:

• So I understand that the charger/power supply has way to many amps. Does this mean that the battery has to many amps as well?

• In regards to getting a new power supple... Would I need a power supply that in 12V 1 Amp?

• If so is there much wiggle room +/- a few Amps?

 

[davenn]

Well... I feel like an idiot... sorry it took so long for me to understand

pleased don't feel that way, it's all a learning process

So I understand that the charger/power supply has way to many amps. Does this mean that the battery has to many amps as well?

in general it doesn't matter if the PSU current capability is higher rated than what the device it's powering requires
The amount of current that flows is determined by the load resistance of the device, not what the PSU is capable of supplying


if you already have that PSU, you can use it. we are just pointing out that you didn't need one with that current capability


Dave

 

[J0n]

if you already have that PSU, you can use it. we are just pointing out that you didn't need one with that current capability

But will this course any damage to the battery/motors?