Emergency lamp

[Bumblebee001]

Hi,

I have managed to make some changes to salvage an emergency lamp that had 4 lead acid batteries connected in parallel with a charging board.

I replaced the board with that from a universal charger that takes Li / NiMH batteries upto 9 V.
I connected this to 3 NiMH AA batteries in series (total 3.5V) housed in a battery case.

The unit has 1 x 2 way switch and an simple on/off switch which I would like to restore to their original purpose. The on/off is currently connected correctly so that I can turn the lamp on and off as expected.

Basically, what I would like to do is to set the 2 way switch in such a way as to allow the LED lights to automatically come on when the electricity supply to the charging board is interrupted such as when there is a power outage.

Is there a simple circuit that can be incorporated?

I can send further details / diagram to show what I have done so far.

 

[Harald Kapp]

It beats me how the 2 way switch would work in this case as a means of automating the lights in case of a power outage.

A very simple way is by using a normally closed relay.
Connect the contacts across the on/off switch, connect the relay coil to the supply voltage.
When there is supply voltage, the relay will be on, the contacts will be open, the lights will be off.
When the power supply drops out, the relay will be off, the contacts will be closed, the lights will be on.
In any case the relay can be overridden by the on/off switch to turn on the lights even with ower supply available.

Yoiu could use the second switch in series with the relay contacts to disable the automatic light on function.

This is what I imagine:

 

[Bumblebee001]

Hi Harald, Thanks for replying

Yes.... looks like what I am trying to achieve. My understanding of a relay is some form of coil that acts as an electromagnet. Is there some electrical component that does this function that I could buy? The original circuitry has no obvious electromagnet or sizeable component that could house one.

I have very basic knowledge of electronics so kindly explain in terms suitably clear for someone venturing into electronics as a hobby.

Regards

 

[Harald Kapp]

A relay is the most simple component in this application.
A solid state relay could be used, but in another configuration as normally closed solid state relays are very unusual (if they exist at all).
You could use a bipolar transistor or MOSFET which would have to be controlled from a circuit which is powered by the battery and supervised the input voltage (e.g. a comparator).

Here is a simple circuit that may be adpated to your needs by replacing the transformer with your power source:http://www.electroschematics.com/6199/automatic-emergency-light/

 

[Bumblebee001]

If I understand the circuit well, it would appear that some components are not needed in my case and others might require to be a different value. The charger should be delivering the required charge in one direction via it's own set of diodes and should be around 330mA according to the specifications of the charger as being used ie to charge 3 x 1.2V (3.6V) batteries. Strictly speaking I should be using 2 batteries only ie 2.4V as the original supply voltage to the LEDs was around 2.2V judging by the type and the way the original Pb acid batteries were set up. However 2 batteries barely lit up the unit so I will keep them at 3.

How should I proceed?

PS I think the LEDs might meed their own protective resistor as I have removed the original circuitry and it does not look like the panel in which these lamps are set have any resistors.

 

[Bumblebee001]

Also - apparently that circuit does not work according to comments made.

 

[Harald Kapp]

I've come up with another solution for replacing the relay:

When external power is present, Q2 is on, pulling the base of Q1 to 0 V. Q1 is therefore off. The gate of the P-MOSFET M1 ist pulled to source potential via R4. Vgs= 0 V and therefore M1 is off. The lamp is off.
When external power fails, R5 pulls the base of Q2 to 0 V. Q2 is offf, tehrefore Q1 is on via the base resistor R3. The gate of M1 is pulled to 0 V via R1, Q1 and M1 is on. The lamp is on.

The switch in series with M1 is used to disable the automatic.
The swizch in parallel to M1 and the other swithc is used as a manual override to turn on the lamp regardless of the state of the external power.

 

[Tha fios agaibh]

Emergency lighting is setup similar to Haralds relay circuit except the function of the switch is to test the batteries on a monthly biases. If this is for emergency or egress lighting you don't want a switch that will disable the lamps from automatically coming on.
Usually just a normally closed switch to disable ac power is used.

 

[Bumblebee001]

Now, I need to translate that so a noob like me can get it done!

I am attaching a crude diagram of what I've got at present.

If I had to order the components, what are Q1 and Q2 and M1?

 

[Bluejets]

allow the LED lights to automatically come on when the electricity supply to the charging board is interrupted such as when there is a power outage.

I for one, do not see why you would want to change the original board as if it was indeed a non-maintained emergency light, this is what it would do originally.

In many instances, there is on-board ability to change between maintained and non-maintained operation as well. Battery charger and monitoring for boost and trickle charging and input for testing as Tha fios agaibh has mentioned.

 

[Bumblebee001]

One of the problems with these units is the battery/ batteries. They are always Lead Acid type and are high maintenance if they are to last.

To simply replace the original Lead Acid batteries would have cost a bomb and remain with the issue of lead batteries. I would have been able to buy around 20 new units for the price of the batteries alone. This would have made no sense. So I decided to change the type of batteries to the commoner, cheaper, less-of-a-problem NiMH or Lithium batteries. To do so required replacement of the charging board.

I already have several rechargeable batteries of the latter types (and of high mAh capacity meaning the unit now lights up for much longer than it did with Lead batteries). I did not need to spend money on new batteries.... I merely spent just over $2 for a universal charger (suitable for both NiMH and Li) which I stripped down and incorporated its board in place of the original. When the NiMH batteries need replacing, all I have to do is simply take them out of the case and put in another set. No soldering or anything.

So far the changes have been successful and I am happy that everything fitted in neatly. What is left is to add the automatic lighting functionality.

Meanwhile I am learning a bit of electronics and contributing positively towards our environment by repairing not throwing away.

 

[Tha fios agaibh]

Rather crude sketch but hopefully you get the idea.
It may be wise to use a separate light/source rather than using battery power during normal (ac power on) use.
That is, If your intent is to use this light while normal power is on.

 

[Bluejets]

One of the problems with these units is the battery/ batteries. They are always Lead Acid type and are high maintenance if they are to last.

Don't know where you found these but in Aus at least, lead acid haven't been used for maybe 15-20 years.
Requirements here are test run must last 90 minutes or more.
Fail, and out they go whollus bollus, no replacing bits and pieces for safety reasons.
Current life span around 5 to 7 years.

 

[Tha fios agaibh]

Around here, Lead acid is still widely used for egress lighting because of cost and availability.
Many are capable of exceeding the 90min rule even with old and inefficient incandescent lamps. These long running lights just take a larger battery, usually around 12v-7ah.

Exit lights on the other hand don't use as much power so they usually require less than 1ah.
Modern Exit lights are usually lithium (lip04) or similar and lead acid batteries are virtually obsolete.

 

[Bumblebee001]

Converting this lamp can be considered at least a practical electronics project.

I would appreciate a reply from Harald Kapp regarding specifications/ values of the 3 components I indicated in my earlier post. It would help me order the correct ones and not risk blowing myself up with the unit!

I will need to draw a diagram of how I would solder the components using a circuit board like the one shown here.

 

[Harald Kapp]

For the NPNs almost any small signal transistor can be used, e.g. 2N2222 or BC107 can be used.
For the PMOS any transistor with a suitable VDSmax > = 10 V and Idsmax >= max. current (depending on the current consumption of the lamp) and last not least a threshold voltage Vgsth >= -2 V (logic level mosfet) can be used.
I could look up one if you give the max. lamp current.

 

[Bumblebee001]

For the NPNs almost any small signal transistor can be used, e.g. 2N2222 or BC107 can be used.
For the PMOS any transistor with a suitable VDSmax > = 10 V and Idsmax >= max. current (depending on the current consumption of the lamp) and last not least a threshold voltage Vgsth >= -2 V (logic level mosfet) can be used.
I could look up one if you give the max. lamp current.

There are 63 LEDs in the unit and are powered by 3.6V. I would have to cut the wire and apply an ammeter in series to give you the value you need unless you can work out a likely value from this information.

The charger itself delivers 360mA at 3.6V according to the specs.

 

[Harald Kapp]

unless you can work out a likely value from this information.

That would be pure guesswork. Assuming 10 mA...20 mA per LED this results in 0.6 A ... 1.2 A.

For example a FDC658AP matches these requirements.

 

[Bumblebee001]

That would be pure guesswork. Assuming 10 mA...20 mA per LED this results in 0.6 A ... 1.2 A.

For example a FDC658AP matches these requirements.

I used an ammeter and it is reading 0.12A (strangely enough I am getting -0.12A to -0.14A [negative value even if leads are reversed with switch on 10A setting) but when I turn the switch of the meter to the 200mA setting I get 0.00mA when I should be getting 120mA)! Am I missing something?

 

[Harald Kapp]

Sounds like your ammeter is not working properly. Did you check it against a known current?