SLA or NiCad???

[patdivelight]

Hi,

I'm planning on making a batterypack to overdrive a MR16 bulb (35Watt/10°).
I prefer the Cyclon SLA batteries, 2 Volts/5Amp (7 pieces= 14Volts)
Would 5Amp be ok to have at least 1 hr of burntime? (I don't know how to calculate the exact Amp used by the bulb in overdrive?)

I know that the voltage on NiCads is much more stable during use. Would I be able to use the Cyclons for this or is it a NO GO?

Thanks!
Patrick

 

[allegfede]

SLA are easy to handle, but better weight/amps ratio is for Ni-mh or Li-Ion (but they need electronic to protect deep discharge)

Federico

 

[Packhorse]

I started off with 2x 12v 2.2ah SLA's but changed to 12 D 5ah Nicads.
Nicads allowed me to use a smaller cannister than the SLAs. Not only because of the greater power/weight ratio but because of the shape of the batterys.
I use 4 colums of 3 cells and this fits nicely in 90mm PVC tube.
SLA batterys do not like to be drained down and doing this offten will reduce thier life.
Nicads allow me to run a higher voltage 12x1.2 = 14.4v nominal. This gives a much brighter light and higher colour temp but does draw more current and shorten bulb life.

35watt / 12 volt = 3 amp so in theroy you should get 100 min burn time but in practice 60 min would be more realistic.

I am doing a test on mine at the moment. I charged it a week ago ( but I think it wasnt fully charged) ran it for 40 min. turned it off for 40 min and ran it again for 40 min. The battery was down to 12.2 volt from a start of 15.4v
Im now charging it backup again and will do another burn test once I know it is fully charged. This was with a 20watt bulb ( 20watt @ 12 volt).

heres some more info
http://www.caralarms.co.nz/Dive light.htm

 

[Packhorse]

I just did a second burn time test with what I assume was a fully charged battery.
Anyone out there monitor the voltage when charging? I get a 18.6volt (1.55v per cell) charge and then it dropped to 18.5v. This is a bit higher than I expected.

Anyway I ran the light for the 40 min on then 40 min off then 7 times on and then off for 15 min, then for another 11min untill the voltage dropped below 13.2v (1.1v per cell) giving a total burn time of 2 hours 36 min.

Bulb is a 20w 12v 7.2ohm
Volts at beginning @ 16v 35.5 watt 2.22amp
@20min 15v 31.25 watt 2.1 amp
@40min 13.7v 26watt 1.9 amp
after 15min run 14.8
14.25
14.78
14.61
14.41
14.06
13.55 25.5watt 1.88amp
after final 11 min 13.2

If I ran it for 2 lots of 40 min like my 1st test I believe it would have only lasted for 100min max based on the voltages. Like wise if I had only ran it for lots of 15min I could have got more time out of it (maybe another 15-20 min).
Which goes to show that these Nicads like a bit of a breather between high current use. as can be seen by thier voltage pick up after the 40min run then rest.

Any way this calculates out to about 5.2amphours of current draw.
Running a 35w or 50w bulb and or extending on times will reduce this quite a bit.