Canister Light Battery Upgrade

[in_cavediver]

Ron:

No it's not, (burn time) on a halogen. That's my point.

Read incave's post above. He summed it up perfectly!

NiMH's are a waste of money when driving a halogen bulb, so I'm finding out.

I think the best "rating" for an SLA for divelight use, is what's called the RC (Reserve Capacity). It's sometimes put on RV or Boat deep-cycle batteries. It's the time, in minutes, that a battery can be discharged at XX Amps and still have a voltage of 10.5V

I may be a tad off here, as I'm doing it from memory, but it's close.
Once the voltage drops below this, it's getting fairly low and starts to turn yellow

Yep, you are correct. Most very high drain devices that use SLA's have some sort of low voltage shutdown to prevent sulfating the batteries. (Potentially permanent damage). You should NEVER run an SLA below 10.x volts. (The specific number does vary sligly with manufactors).

From my very non-scientific testing of a SLA under load, the light begins turning yellowish around 11.2-11.5 volts. A really good indicator to shut the light down. One of these days I plan to do a full discharge on an old battery to really characterize what that part of the discharge curve looks like. (Time and light characteristics)

This fact is one of the main reasons I advocate sizing your SLA packs to use a 50% value of the rated Ah rate. It will keep from deep cycling the battery and should give longer life.

Mike

 

[in_cavediver]

I guess I'm going to find out for myself since I already ordered a custom 9ah NIMH pack. I plan on only using a single 100 watt halogen lamp, so hopefully that won't be too hard on the pack. The $25 4ah NIMH pack seemed to do fine on repeated burn tests with a single 50 watt halogen lamp.

I wish you the best and it should work. You won't see any great dramatic increases in burn time but you will see a reduction in the canister size. For my taste's (and burn times), a 50 watt bulb on a 4Ah pack wouldn't give enough burn time. (Full use of rated capacity is 1Hr) I know NiMh tolerate a deeper cycle than SLA but it still seems hard on the pack.

Out of curiousity, what type of burn time have you seen with the 50 Watt light?

Mike

 

[in_cavediver]

unfix8r:

If it is designed for SLA's then it would work, but honestly, the thing wasn't design to "charge" batteries for a living, but it's more of a battery "maintainer".

How long will it work? Who knows, but it only cost $5.00

Battery chargers are real cheap too. And that's their full-time job.

Yeah but if you really look at the UPS, they have a 0.25-1.0 A/hr charge rate on float charger. They are really maintainers, hence the float charger but are equally adept at charging the batteries. I personally use a 0.75 A/hr and 0.6A/hr float charger to maintain my 7Ah batteries. And at $5.00, I'd say that was a good deal. Especially if you don't need a high rate charger. (There are issues in charge rates on small capacity SLA's). I gave closer $15 to make the 2 float chargers I have!

Mike

Mike

 

[ronrosa]

I wish you the best and it should work. You won't see any great dramatic increases in burn time but you will see a reduction in the canister size. For my taste's (and burn times), a 50 watt bulb on a 4Ah pack wouldn't give enough burn time. (Full use of rated capacity is 1Hr) I know NiMh tolerate a deeper cycle than SLA but it still seems hard on the pack.

Out of curiousity, what type of burn time have you seen with the 50 Watt light?

Mike

I've done 3 separate burn tests. I stopped each test around 45-50 minutes. Light color was not yellow, battery voltage was around 11.2 amps.

I could have let the test go longer to see exactly when color started to drop off, but this is a test pack and I just wanted to see if it worked. I estimate it could have continued to 52-60 minutes.

 

[ronrosa]

I wish you the best and it should work. You won't see any great dramatic increases in burn time but you will see a reduction in the canister size. For my taste's (and burn times), a 50 watt bulb on a 4Ah pack wouldn't give enough burn time. (Full use of rated capacity is 1Hr) I know NiMh tolerate a deeper cycle than SLA but it still seems hard on the pack.

Out of curiousity, what type of burn time have you seen with the 50 Watt light?

Mike

Forgot to reply to the increased burn times. The NIMH 4ah pack had burn times similar to my 8ah SLA pack using a 50 watt halogen. 4ah NIMH shutdown on thermal safety with a 100 watt halogen. That is why I ordered a 9ah NIMH pack. 8ah SLA gave me around 20 minutes w/ 100 watt halogen. 9ah NIMH is smaller than the 8ah SLA and hopefully will give me burn times of 45-50 minutes. That would be perfect for 1 night dive or 2 day dives.

 

[in_cavediver]

Forgot to reply to the increased burn times. The NIMH 4ah pack had burn times similar to my 8ah SLA pack using a 50 watt halogen. 4ah NIMH shutdown on thermal safety with a 100 watt halogen. That is why I ordered a 9ah NIMH pack. 8ah SLA gave me around 20 minutes w/ 100 watt halogen. 9ah NIMH is smaller than the 8ah SLA and hopefully will give me burn times of 45-50 minutes. That would be perfect for 1 night dive or 2 day dives.

Its kind of nice to know that the math actually translates well into the real world for the NiMH. As for your SLA though, it appears to be very sulfated/pitted. I can get 25 minutes off a 7Ahr battery and a load of 150 watts without hitting the red zone on the voltage (Less than 11.4 V)

Good luck with new NiMh pack and let us know how it works out

Mike

 

[DeepScuba]

Hmmm, what's that 9Ah NiMh cost you???

 

[ronrosa]

Hmmm, what's that 9Ah NiMh cost you???

$90 assembled shrink wrapped with a tamiya connector at batterystation.com. 9.5ah for $98 at batteryspace.com.

 

[ronrosa]

Hmmm, what's that 9Ah NiMh cost you???

UPDATE:

Received my 9ah NIMH pack from batteryspace.com for $98. Pack fully charged in 4.5 hrs with their $60 charger. 2 burn tests conducted with 100 watt halogen lamp. Ended both burn tests at 1 hour, battery still going strong, light color not yellow.

Here is a picture next to a 8ah SLA.

NIMH Pack is 8.5 inches tall, by 2.75 inches diameter.

Next step, call AUL (American Underwater Lighting) for a custom canister.

 

[DiveGolfSki]

Can anyone tell me what the advantages are between NiMH over Lead Acid? I've been following this thread and clearly NiMH are superior but is the cost differential worth it. Assuming a dive only lasts for an hour and using a MR16 50W bulb, wouldn't a Sealed Acid 7amp 12v battery last long enough?