I converted my 4 D-cell 750 lumen lantern to 5 cell NiMh

I have this 750 lumen camping lantern that I absolutely love for not only camping but also just night lighting anytime, anywhere I need it.

But it uses disposable batteries and all these lanterns come with provision for 3 or 4 batteries (that I know of)
So I made a 5 cell rechargable battery holder to replace the 4 cell battery holder that they come with.
Now I can use 5 - 1.2v rechargable 11000 mAh Tenergy batteries and get the 6v needed plus get some excellent runtimes

Maybe they already have some that hold 5 cells? Dunno.
What do you think? Waste of time or cool conversion?

You don't really NEED to run five NiMH in place of four alkaleaks. Although voltage is nominally higher with alkaleaks, it is the same or lower most of the time in real world use. Four NiMH would work fine.

I was wondering... did 4 NiMH batteries not power it?

holygeez03 said:

I was wondering... did 4 NiMH batteries not power it?

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They did, but I'm not sure what the cut-off voltage point is. It calls for 6volts. I didn't test the cut off point for the diodes but with the 5 cells it's not much concern.

I just thought the 10,000 extra mAh would be good = 50,000 mAh.

4 batteries is 40,000mAh

When I'm camping (or whatever) longer run times at brighter lumens seems like a good idea no?

Is longer run time a bad thing StorminMatt and HolyGeez?

OttaMattaPia said:

Is longer run time a bad thing StorminMatt and HolyGeez?

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It isn't. But my biggest concern here would be whether the higher voltage may damage your lantern. Also remember that capacity does not add when cells are in series. The only reason five cells might increase runtime would be if the lantern cuts off power at too high a voltage. And because the voltage of alkaleaks drops rather drastically as the batteries are discharged (unlike NiMH), I'm guessing the lantern will work fine down to 1.0V per cell (which is fully discharged for NiMH).

StorminMatt said:

It isn't. But my biggest concern here would be whether the higher voltage may damage your lantern. Also remember that capacity does not add when cells are in series. The only reason five cells might increase runtime would be if the lantern cuts off power at too high a voltage. And because the voltage of alkaleaks drops rather drastically as the batteries are discharged (unlike NiMH), I'm guessing the lantern will work fine down to 1.0V per cell (which is fully discharged for NiMH).

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You're right. I'm increasing the voltage but not the capacity......hmmmm

But I suppose it will hold it's voltage above cut-off for a good bit longer. Which still kinda acts like capacity anyway.

As far as over voltage.....are you referring to the fully charged state of NiMh batteries at around 1.4v ?
So 1.4 x 5 = 7 volts

So for a while, I would be running 7 volts through my LED's

I see your point(s)

I guess I could add a $3.00 Buck DC to DC converter inside to ensure the voltage never goes over 6v ?

Maybe my external 16v Lipo going through the DC to DC buck converter was the best idea?

OttaMattaPia said:

They did, but I'm not sure what the cut-off voltage point is. It calls for 6volts. I didn't test the cut off point for the diodes but with the 5 cells it's not much concern.

I just thought the 10,000 extra mAh would be good = 50,000 mAh.

4 batteries is 40,000mAh

When I'm camping (or whatever) longer run times at brighter lumens seems like a good idea no?

Is longer run time a bad thing StorminMatt and HolyGeez?

Click to expand...

Adding cells in series does not increase mAh.
There is still only 11000mAh in that light.

Also, just because it says 11000mAh on the label does not mean it actually is 11000mAh.
I looked up some tenergy battery discharge curves on google and you can probably expect ~75% of what is on the label.

OttaMattaPia said:

You're right. I'm increasing the voltage but not the capacity......hmmmm

But I suppose it will hold it's voltage above cut-off for a good bit longer. Which still kinda acts like capacity anyway.

As far as over voltage.....are you referring to the fully charged state of NiMh batteries at around 1.4v ?
So 1.4 x 5 = 7 volts

So for a while, I would be running 7 volts through my LED's

I see your point(s)

I guess I could add a $3.00 Buck DC to DC converter inside to ensure the voltage never goes over 6v ?

Maybe my external 16v Lipo going through the DC to DC buck converter was the best idea?

Click to expand...

The big unknown here is exactly what kind of circuitry this lantern employs. Since it runs an LED from four alkaleaks, it may already have buck circuitry (similar to 4xAA lights like the Nitecore EA41). If this is the case, then you are probably OKAY with five NiMH cells as it stands. Five NiMH cells would also increase runtime vs four. Of course, there are two other possibilities. One is that the lantern employs a linear driver. This simply burns off the extra voltage as heat, and will not improve runtime with five cells. But five cells probably won't hurt anything - at least as long as the driver can dissipate the extra heat over the long haul. Finally, it could be direct drive with a resistor. This is a worst case scenario. And it is quite likely with a relatively low cost camping lantern. With the extra voltage and without the extra internal resistance of alkaleaks, the LED will get WAYYYY too much voltage, and could burn out at some point.

Your lantern looks to be running COB panels which are typically about 3.5v or so I'm guessing as others have stated it has a buck stepdown circuit. I seriously doubt it is a linear regulator as it is too much voltage (power) to throw away as heat with 4 cells.... 3 cells I could imagine it as a possibility but these days buck and boost circuits are pretty cheap to make by manufacturers.
If you are able to take it apart you should be able to use a voltmeter to measure the voltage to the COB LEDs and perhaps even inspect the electronics.

Enderman said:

Adding cells in series does not increase mAh.
There is still only 11000mAh in that light.

Also, just because it says 11000mAh on the label does not mean it actually is 11000mAh.
I looked up some tenergy battery discharge curves on google and you can probably expect ~75% of what is on the label.

Click to expand...

Yeah, seems I forget basic electronics 101

Thanks for the assist everyone. Nothing gets past you guys :twothumbs

My original setup with the external 5200 real mAh LiPo battery is looking better and better.

Lynx_Arc said:

Your lantern looks to be running COB panels which are typically about 3.5v or so I'm guessing as others have stated it has a buck stepdown circuit. I seriously doubt it is a linear regulator as it is too much voltage (power) to throw away as heat with 4 cells.... 3 cells I could imagine it as a possibility but these days buck and boost circuits are pretty cheap to make by manufacturers.
If you are able to take it apart you should be able to use a voltmeter to measure the voltage to the COB LEDs and perhaps even inspect the electronics.

Click to expand...

Other than applying over voltage and see if it steps it back down, is there any other way to see if it has a built in buck converter?

Well, I guess if I take it apart I might be able to make out the components of a buck converter

OttaMattaPia said:

Other than applying over voltage and see if it steps it back down, is there any other way to see if it has a built in buck converter?

Well, I guess if I take it apart I might be able to make out the components of a buck converter

Click to expand...

There is a way to tell if it is using a buck regulator you will have to put an ammeter inline and check the current using 4 cells then 5 cells and if there is a buck circuit the current should drop the higher the voltage goes.

OttaMattaPia said:

Yeah, seems I forget basic electronics 101

Click to expand...

No problem, sometimes I forget how shoe laces work xD

Enderman said:

Adding cells in series does not increase mAh.
There is still only 11000mAh in that light.

Also, just because it says 11000mAh on the label does not mean it actually is 11000mAh.
I looked up some tenergy battery discharge curves on google and you can probably expect ~75% of what is on the label.

Click to expand...

Dog gone.

I was looking at some actual tests done by folks over at BudgetLightForum.com and at least one of the gurus over theresaid those particular batteries were "certified" to make the output they claimed and that in their tests, it often slightly exceeded the 10,000mAh.

Have people here tested them and gotten different results?

Very cool idea Otta.

Please tell us as time goes by how it works out.
If it ends up it went ... well ya know not to do that again.

bykfixer said:

Very cool idea Otta.

Please tell us as time goes by how it works out.
If it ends up it went ... well ya know not to do that again.

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Thanks bykfixer
I got to play with my toys and do what I like so it's a win regardless

Here's my other camping lantern that I modified to use with a 5200mAh RC LiPo battery that I couldn't use in an aircraft....
This was my original "extended runtime" option until I started trying to do a 5 battery option on the other (that idea may not fly...no pun intended)
Anyway...THIS is working exactly as planned fortunately.....

There's a buck board DC to DC converter, a low cell voltage warning device and I added the attachment for it all to sit on and attach to the lantern for easy carrying and added a coaxial DC power plug to plug in the power from the contraption. Not as "pretty" as the 4 batteries inside but I found a use for my $35.00 big LiPo battery and it sure will run a long time!
Most of all, it's just fun messing with stuff like this.

If anyone sees any potential errors I made that could cause problems please advise.