Stoker battery power...


 

Alec

New member
All,

I'd like to power my Stoker from my truck battery. I know there are a lot of 12v to 120v inverters out there - I already have an 800w inverter. However, I'd like to pass on the inverter and go directly from 12v to 5v. I have found a high efficiency (>93%) converter that can deliver 3A max. Are there any EE's out there who can render an opinion on whether this will work or not.

The data sheet for the converter is here: http://www.cincotek.com/minilynx_sip_12v_ds.pdf

It looks to me that I just need to get the part and wire 12v in and feed the 5v out to the Stoker...

Thanks -

Alec
 
I think it would work. But you should put it in an insulated box and put an inline fuse on the wire. You don't want to short out a 12 volt car battery.
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Efficiency will be well under 93% though as the stoker most of the time won't be using much current. The inverter is much less efficient when it is lightly loaded (around 70-80%).
 
If 1 amp would work you can buy a 12v to 5v DC converter in a cigarette adapter confirguration for cheap. A google search turned 1 up for under $5.
 
Originally posted by A. Vale:
If 1 amp would work you can buy a 12v to 5v DC converter in a cigarette adapter confirguration for cheap. A google search turned 1 up for under $5.
Did it say it used a swtiching power supply? If not, it will be very inefficient (about 40%).

But you are probably right that stuff like this is available off-the-shelf. So only do it for the fun of it.
 
Data sheet claims 93% efficiency - we'll see...

Here is the part:

part.jpg


I ordered the part from Digi-Key. They shipped it the same day - I got it yesterday... About $7.70 for the part and $2 shipping plus some tax to Texas. The item number was 555-1052-ND. It's so small I can wire it up as an inline converter - this should be interesting !!!

Alec
 
thanks Alec. I'm going to order one as well. Maybe 2 to have one on hand. My only concern would be how the device fails. If it shorts would it supply 12 VDC to the stoker???

-rob
 
The data sheet claims that the device has circuitry for overloads. I guess the probability of the device failing is not much more then an inverter failing - maybe less...

My concern is how well the device handles the battery current. You might want to hold off ordering parts until we see how it actually works
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Alec
 
Originally posted by Alec:
Data sheet claims 93% efficiency - we'll see...
That is the peak effiency at maximum power usage. At low usage likely of Stoker, its efficiency drops to levels I mentioned (see the graphs in the spec).
 
Hah !! I guess I'm hoping that it will power my Stoker for my BBQ competitions and leave enough juice for me to start my Hemi
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Alec
 
I measured my Stoker's current usage with a Fluke clamp-on current probe.

Configured with 5 probes and 2 5CFM fans and connected Ethernet, it used:
1.05A with both fans running
0.36A with neither fan running
With a single fan, we would expect to see
0.7A with 1 fan running

At the idle current, efficiency (from the graph) is at approx 82% or 2.2 watts from the source.

With a single fan on, efficiency is at about 88% or 4 watts from the source.

Assuming a fan duty cycle of about 10% over the duration of the cook this gives a average wattage of about 2.37.

This, in turn implies an average current of about 200ma on the 12V source. Over a 18 hour cook that means battery usage of about 3.6AHr.

A $80 trolling battery (deep cycle type) might be rated at 90AHr. While car/truck starting batteries are optimized for different uses, you should have no problem with starting it later even after quite a few hours of cooking. You would use more current with the dome lamp or the radio on.

You might consider a separate battery rather than tying your truck to the cooker. Otherwise, the quick trip for a forgotten item would be problematic.
 
John,

Great analysis !! Thank You !

When I get it wired up I'll post some pictures on the rig and let you know how it works...

Alec
 
OK, I spent some time over the weekend and wired up the MiniLynx power supply for the Stoker. Here is a picture of the final product:

power.JPG


I did not wire up the auto on/off or the Voltage Margining. I could only find a 1.5k resistor at Radio Shack - that was the closest I could get to the 1.472 that was needed for 5 VDC output. The 1.5k resistor set the output at about 4.85 VDC (a little low). I checked the regular Stoker 120V power supply and it was putting out about 5.3 VDC. So, I had a 10k pot lying around from another project and I replaced the 1.5k resistor with the 10k pot. This way I could adjust the resistor setting from 0 to 10k and since I only needed 1.47 I just cranked the pot down until I got the voltage I wanted. The MicroLynx is really sensitive to the resistor value. In any case, I just adjusted the pot until I got 5.20 VDC out. I wired the supply to a cig lighter plug with an internal fuse and 25' of wire...

The next step was to see if it would power the Stoker and my 10 CFM fan and the temp probes. I plugged in all the Stoker attachments, plugged in my MiniLynx power supply and, somewhat cringing, hit the power button on the Stoker. The Stoker started right up, tested the fan (as it always does on startup), finished initializing and then powered the fan back on just like it would if it was attached to my pit. This looks like it'll work pretty nicely.

The stress test will be at a cookoff this weekend... I'll let you know how that goes.
 
Nicely packaged.

Beware that the no-load voltage may not be as directly related to the load voltage as you might hope. In other words, that the Stoker showed 5.3 doesn't mean it was even close to that under load. Much better (but harder) to measure voltage under load.

That said, if you measure 5.2 from your circuit under load, then that is within 5% which is quite good enough.

You can usually find a 1K and a 470 Ohm resistor in most shops (for series connection). I would prefer fixed resistors over a pot because they have much better long term stability. If you can, measure the value you settled on (from the pot) and find a combination of resistors that would come out about the same.

You could always test the overnight performance by connecting the stoker and fan during the week and letting it run all night without a fire (100% duty cycle). If your battery survives that, you will have no problem with a more reasonable duty cycle. And you probably have a battery charger at home, if it does not.

What's more important? Getting to work on time or getting the meat done on time?
 
John, that's good feedback - thanks.

There is a voltage margining circuit built-in the the MiniLynx which will keep the voltage within a specified range as the load changes. I didn't wire that up but it's always an option if there is a voltage problem under load.

I'm not a EE - I know just enough to be dangerous
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I wondered about running multiple resistors but I wasn't sure about parallel vs serial. Your comment indicates that I would need to wire them up serially - I may just try that...

Alec
 
Well, I finally had a chance to run my Stoker off of my custom power supply for an entire cook yesterday. Plugged the power supply into my truck cig lighter at 6:00 AM yesterday and ran the Stoker all day (until 3:00 PM). The Stoker + temp probes + fan ran perfectly fine all day and, better yet, I could still start my truck when I was done
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One more note on the construction. I removed the 10k pot and replaced it with a 1.4k ohm resistor. This gave me a fixed output of 5.1 volts. I had to wire up a combination of resistors to get to exactly 1.4k since I could not find an exact match... Thanks to John Brisbin for the suggestion...

Alec
 

 

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