Ah ha, because that 48W/4A rating is at the efficient temperature.
Datasheet here [1]. The L298N is a cheapie. Looks like transistors,
not mosfet, and it won't limit current, that's up to you. Confirming
what you said, at least the application notes do say running two in
parallel is allowed, whew.
I don't know how to do the current sensing, but the L298N provides sense
pins.
Thanks for the tips, Daren.
John
[1]: http://www.st.com/resource/en/datasheet/l298.pdf
On 11/01/2017 10:59 AM, Daren Schwenke wrote:
Just hook up your power full on in one direction and let it equalize so
the junction is at temperature.
Then reverse the power leads and measure the current.
It will probably exceed your 48W/4A rating until the junction
temperature differential swings the other way.
If you are using a motor driver chip, it will probably limit the max
output current for you.
I don't know if the L298N has a mosfet output stage. It probably does.
If your input timing is good, then running two in parallel should work
fine.
Just wanted you to be aware of the possibility of you browning out your
supply when people do silly things like switching from full cool to full
heat.
On Wednesday, November 1, 2017 at 11:40:10 AM UTC-4, John Morris wrote:
On 11/01/2017 10:15 AM, Daren Schwenke wrote:
> When switching peltiers between heat/cool mode you can get some
really
> high currents.
I don't know much about it. This one is rated 48W/12V, so I used a
cheapo L298N module, 2 channels at 2A/channel, wired together. (I'm
not
sure if that's allowed, but it seems to work.) Do you mean higher
current than 4A?
> You may want to include some current feedback and perhaps limit
your PWM
> during switching, or just keep it from doing that with your PID.
I still need to stick PID comps in there. Right now, it's a dumb
switch, which is why the curve in the time series chart is so bad.
By "current feedback", do you mean monitor current through the Peltier?
How do I limit the PWM? Sorry, you're going to have to spell it out
for
me. I'm pretty bad at electronics.
> On Wednesday, November 1, 2017 at 11:04:36 AM UTC-4, Daren
Schwenke wrote:
>
> Neat idea, and perfect name. :)
Thanks!
John
>
> On Tuesday, October 31, 2017 at 2:07:09 PM UTC-4, John Morris
wrote:
>
> I'm working on this Machinekit-based weekend project, the
> "Goldibox"
> [1]. Kind of like a cross between a fridge and an
incubator,
> you set
> minimum and maximum temperatures on its thermostat, and
as the name
> implies, the Goldibox will keep its contents not too hot,
not
> too cold,
> but just right.
>
> The last major piece I'd like to do is improve the GUI,
but I'll
> need
> some help. First, take a look at this mock-up of a fancy
> thermostat
> [2], which combines quite a few controls and gauges into
one.
> If this
> isn't a very difficult thing to program using either QML
or C++
> code,
> I'd do it. Second, below the thermostat, I'd like to add
a small
> version of the time-series graph (see [1]). This is
generated
> on the
> Goldibox, and would need to be fetched by the remote GUI.
>
> Other than that, it needs a PID control and a few cleanups
> before it's
> done, and then I'd like to show it off to the Machinekit and
> (Pocket)Beagle communities. It seems like the project
could be
> interesting because it integrates the (brand-new)
PocketBeagle,
> electronics, Machinekit and QtQuickVCP, and as such
represents a
> demo of
> the complete chain from hardware to phone app. At the same
> time, it's
> still fairly simple, with complexity just a step above
Alex's
> AND-Demo.
> Of course it's all open source, and I tried to make it
easy for
> anyone
> to try out the simulator in Docker by running just a few
> commands (but
> expect a few minor hiccups ATM if you do).
>
> I'd highly appreciate help with the GUI, and I welcome your
> comments
> about the project.
>
> [1]: https://github.com/zultron/goldibox
<https://github.com/zultron/goldibox>
> <https://github.com/zultron/goldibox
<https://github.com/zultron/goldibox>>
> [2]:
>
https://docs.google.com/drawings/d/1ixn3tSA8_OyTdZ1lz5k4MWjTZ9rEFJM9or3oYW8NuUA/edit?usp=sharing
<https://docs.google.com/drawings/d/1ixn3tSA8_OyTdZ1lz5k4MWjTZ9rEFJM9or3oYW8NuUA/edit?usp=sharing>
>
<https://docs.google.com/drawings/d/1ixn3tSA8_OyTdZ1lz5k4MWjTZ9rEFJM9or3oYW8NuUA/edit?usp=sharing
<https://docs.google.com/drawings/d/1ixn3tSA8_OyTdZ1lz5k4MWjTZ9rEFJM9or3oYW8NuUA/edit?usp=sharing>>
>
>
> John
>
> --
> website: http://www.machinekit.io blog: http://blog.machinekit.io
> github: https://github.com/machinekit
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