Royal Guard Helmet Fans - one modest solution (out of many)

[domz]

Hi folks,

Some of you might have noticed in the run up to Chingay 2010 that I stuck fans in the RG helmet. I've been tinkering with this for quite some time and I think I've more or less settled on a good workable system, so it's time to upload something for future costumers, especially Royal Guards.

Ingredients

Basic tools like soldering iron, etc.
2pcs of 4 x AA parallel battery pack
2pcs 12V 1.5A tube fans
Wires and sleeves

... and a connector. This one was salvaged from a fluorescent light fixture. I have no idea where to buy it. Everything else could be bought at Sim Lim TOWER.

Circuit Diagram



I can't make nice diagrams. Batteries in series, fans in parallel.

Note: this is the BASIC design. It really doesn't look that way when applied to the curves of helmet. That would look more like ...



... like the Stethoscope of Doom.

Being totally clueless at physics, I learnt the hard way that connecting fans in parallel doubles the current, making them spin like the PC fans they're supposed to be. As opposed to when I connected them in series for the full-dress rehearsal. Those were hamster wheels.

Pics!



This is the RHS fan. The original PC connectors and Earth wire were cut. I used the two-wires-stuck-together kind for cabling. I might add grilles to the fan, just in case (also bought at Sim Lim Tower).



Location of fans in helmet.



Sleeved wires with cable holders. I'm thinking of changing to wider cable holders.



This shows the LHS fan, also pointing down. It also shows where the LHS fan meets the "main wire". The "main wire" was bared (use penknife to carefully cut away some insulation along a certain section, thread the other wire in. Repeat several cm away for the other one).

No sleeving for the LHS descending wires, because I lack skillz.

Also, the descending sleeve is red



Helmet end of the connector, with visible ratings.



Back of connector, showing screwings.



The battery end of the connector.



Battery packs connected in series.

Have fun!

[HyBRiD]

those fans look like the ones on the graphic board =D

[domz]

I think graphic boards are more intelligent and generate less heat though (=

Come to think of it, I dunno if the fans are spinning at max speed. How to calculate ah? They're rated 1.5A but I dunno how to calculate output by the batteries.

[HyBRiD]

should be printed on the fan bro

[domz]

I'll take a closer look but the main piece of sticker with the volts and amps are covered by velcro hahahahaha.

[HyBRiD]

lol your fault then.. btw, if u can make one with 3 speed switch =D u might wanna head down to sim lim tower and see if anyone there can get it done. =D

[domz]

Don't think I'll do that because:

1. I probably don't need a 3-speed switch - given my blubber I'll just need to switch between "Off" and "MAXIMUM POWER PLEASE".

2. No time, and more importantly, no skillz.

[HyBRiD]

well it's just a 2 step switch like the on off switch on most toys.. i have one on my amd chip it's pretty cool it works like this 1-2-3 so u can just simply move from 1 to 3 in an instant i believe its a slight increase in voltage im guessing.. or u could try with a higher powered batt.. dun forget the fuse =P how bout find a fan with higher rpm =D

[domz]

Went for the biggest fan that could comfortably fit my helmet, taking into account the optimal location of the fans within the helmet. Not that I know anything about fluid dynamics or thermodynamics - I simply went by agaration.

Oh well. I guess this is a work-in-progress. Once I swap out the cable holders for wider ones (juuuuuuuust bought them last night) I'll find some way to fix the grilles and then there will be other priorities taking over for this as well as my second costume (it's a SL).

[recon]

Hi dom,

In general, for a load with resistance R, the current
supplied by the battery is:

I= V / (R + Ri) (Ohms law for equivalent circuit)

Ri is the internal resistance of the battery

Presuming you are using Energizer brand AA batteries, rechargeable NiMH type. 2500 milliamp-hours

If you place 2 x 4 parallel AA (1.2V) batteries in SERIES, the resulting voltage
adds to 2.4 volts but the current capacity = 10 amp-hours

If you place 2 x 4 parallel AA (1.2V) batteries in PARALLEL, the resulting voltage = 1.2 volts and the current capacity = 20 amp-hours.

Connecting batteries in series will not give you more
amp-hours aka more usage time. Also, the maximum current that can be supplied is the same with one battery or 2 in series. Only the voltage is doubled.
There is no minimum current.

From the circuit configuration i see, the fans would run as it meets the basic current requirement to operate it, but suffers in the power category (P = IV) which would lead to the battery being drained faster

Either you can change the battery to a higher Volt and current series for e.g. 12V or change the fans to one that consumes less power, voltage

[domz]

An engineer!!!

The batteries I'm looking at are rated 1.5V. There's eight of them all[/] parallel. Translates to 12V, right?

Question: how did you arrive at 10 amp-hours?

Also, I'll need the batteries to last long enough for each performance (but not necessarily including waiting time - I've rewired it to make it easy for me to disconnect and remove helmet during waiting time and to connect when we're really moving). The fans are rated 1.5A, does this mean a 2.5 amp-hour cell will last 1h40min? Or half that, since there are two fans in series? (assuming connecting cells in series doesn't affect the amp-hours)

[recon]

An engineer!!!

The batteries I'm looking at are rated 1.5V. There's eight of them all[/] parallel. Translates to 12V, right?

Question: how did you arrive at 10 amp-hours?

Also, I'll need the batteries to last long enough for each performance (but not necessarily including waiting time - I've rewired it to make it easy for me to disconnect and remove helmet during waiting time and to connect when we're really moving). The fans are rated 1.5A, does this mean a 2.5 amp-hour cell will last 1h40min? Or half that, since there are two fans in series? (assuming connecting cells in series doesn't affect the amp-hours)

Hi dom,

Nopes batteries arrange in parallel means the voltage supplied to the load would be the same as a single cell 1.5v battery, only connecting all 8 of them in series would give you a output of 12V supplied to the load but that would be heavy. But you could do is connect two 9V batteries in series, which would suffice for your needs

10 amp-hours = 2500 milliamp-hours multiply by 4 due to the parallel configuration of 4 batteries. Bascially paralleling any power source gives an increase in current but the same voltage.

Since your circuitry is wired in a series configuration of 2 x parallel (4 x 1.5V batteries), which would give a voltage of 3V and 10 amp-hours across the load (fans), there is two possible situations:

1) Fans wired in parallel, will give a battery life of 10 divided by (2 x 1.5) ~ 3.33 hours

2) Fans wired in series, need 24V (12V multiply by two) but the same current source of 10amp-hour, which would give a battery life of 10 divided by 1.5 ~ 6.66 hours. This configuration wun work as the power requirement for the fans in series far exceed that which is supplied by your current configuration

But all these are based on the assumption you are using rechargeable NiMH AA batteries not regular ones

Here is a sample of how a basic fan controller (speed based) should look like:



Bascially you dun have to use high end GPU card fans as those are power leechers, you can get those normal CPU fans like 40mm x 10mm 5V Fans, which consume less power. For switching the fans off/on, you can use a 2 way or 2 action minature switch and to regulate speed of fan by limiting the voltage supplied to them, you can use a variable resistor or potentiometer

[domz]

Oops my mistake my batteries are all in series (see circuit diagram)

2 x 9 series = 18 no problem with over-volting? Haven't checked the mAh for those yet

[recon]

Oops my mistake my batteries are all in series (see circuit diagram)

2 x 9 series = 18 no problem with over-volting? Haven't checked the mAh for those yet

Nopes, no problems with over volting as the load aka fans would draw what it needs. But im not so sure about the 9V batteries as their current milliamp-hour maybe lower than NiMH batteries thus a shorter operating hour

[HyBRiD]

might as well use lithium polymer.. but well i don't know if the stability issues have been resolved yet. =D we don't want the battery blowing up in the bucket.. =S