Mixing One Alkaline with Five NiMh - is it OK?

[LightScene]

What will be the result if I mix one alkaline AA with 5 NiMh AA's? I'd be using this configuration to drive a 5W luxeon. It seems to me that the alkaline will increase the internal resistance, and therefore limit the current a little. I don't know what kind of negative consequences to expect.

 

[DrJ]

.

 

[Roy]

My gut feeling is ...DON'T!
I suspect that the alkaline is going to get VERY hot and possibly go bang.

 

[evan9162]

You could cause the alkaline to get very hot, over-discharge, and possibly leak, catch fire and/or explode.

When battery makers say don't mix different types/capacities of batteries, they do so for a reason. When device makers say the same thing, it's also for a reason.

 

[pyro]

Why not using a seperate resistor?
When there is no place in the head, thats what i did for using NiMH cells in my SpaceNeedle:
Two thin aluminium disks that fit in the battery tube, the resistor mounted between the disks.
I can use it, or not, only depending on the desired resistance

I would stay away from the light when testing different chemistries in it.

 

[LightScene]

[ QUOTE ]
You could cause the alkaline to get very hot, over-discharge, and possibly leak, catch fire and/or explode.

[/ QUOTE ]

LOL - I'll be the first suicide bomber to use a 3D M@g.
That's pretty scary rhetoric, but what's the logic behind it?

Since the rechargeables have less internal resistance, it seems like the alkaline probably won't be able to contribute as much current as an additional NiMh would.

I just finished testing this configuration by letting it run for 10 minutes. There was no heat below the M@g switch. When I removed the battery packs they weren't even warm.

Since I'm using a home-made battery pack, I don't feel like taking it apart to test the voltage in the alkaline battery right now, but I'll check it after I've used the battery pack for an hour or so.

The current flow in this configuration is just below 1 amp. I'm using a used alkaline with a voltage reading of 1.45.

 

[DrJ]

.

 

[LightScene]

[ QUOTE ]
Why not using a seperate resistor?

[/ QUOTE ]

I've been using the light with 6 NiMh, and that works fine. I've let it run for over half an hour at a time, several times. It's really bright and delightful. So I don't need a resistor, but I needed one more rechargeable for another light, so I figured I could run the 5 Watt on 5 batteries, and one dummy. But when I started to put it together, I thought, why not just put the alkaline in without converting it to a dummy. Then I thought it was best to check with you guys to see if there's anything to worry about.

Thanks for the tip on how to include a resistor with the battery packs. I was thinking in that direction myself, but your solution is better than what I was thinking of.

I have a Reactor 3 which comes with a 2.4 ohm resistor, and I might like to replace it with something a little smaller.
I like the idea of being able to change resistance depending on what kind of batteries I'm planning to use, and what condition they are in. Thanks again.

 

[LightScene]

[ QUOTE ]
I was also worried that the NiMH cells might be harmed when they were almost discharged

[/ QUOTE ]

Yes, I have to be careful not to let any of the batteries get discharged. I was expecting that the light will suddenly get dim when they batts cannot deliver enough forward voltage, or enough current, 1 or the other???

Presumably, the alkaline will create a lot of resistance as it's power gets low.