Solar Cycle Analyst?

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the e wind
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Solar Cycle Analyst?

Post by the e wind » Jan 17, 2018 10:29 am

Hi all, I have an open question regarding the Cycle Analyst, and specifically, how it is used to measure solar power input to your bike.

I propose that it would be very useful to purchase a Cycle Analyst that utilizes two shunts; one for solar input, and one for motor output. This way, your bike would be able to accurately display input & output power with one gauge instead of using a second meter. Some people use the $15 solar meter from Amazon, and some people use a second Cycle Analyst to measure solar power. The only issue with using a CA to measure solar is that the solar power reads negative, and also, you shouldn't have to mount two CA's on your handlebars when one would do the job. I think the CA has enough juice to handle the task if wired & programmed properly.

And theoretically, once we're measuring both parameters on the same device, you could set the bike's power output to match the expected solar input of the day; i.e. instead of selecting a pedal assist mode, or using the throttle, you could set the pedal assist level based on how much power you are making. This would take all the brain-work out of riding a solar bike. Now granted, knowing how much power to use on your solar bike is not that hard; it generally just involves paying attention to a couple meters, and crunching a numbers over coffee/lunch breaks to make sure you'll have enough range for the day. After doing that a few times, you generally know how much power you can get away with using, but wouldn't it be slick if your bike ALWAYS knew what the particular day's range limits are/will be?

A little birdie told me that Grin will be sponsoring the Sun Trip 2018's technical logging requirements. I wonder if they're going to issue a specially programmed Cycle Analyst for data collection of the competitors? And if so, I wonder if they'll optimize the Cycle Analyst for solar in this way?

Tell me what you think, nerds!
E-Bikes are like E-mail.

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amberwolf
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Re: Solar Cycle Analyst?

Post by amberwolf » Jan 17, 2018 1:46 pm

the e wind wrote:
Jan 17, 2018 10:29 am
The only issue with using a CA to measure solar is that the solar power reads negative,
That depends on which way you hook up the shunt. If current flows from the shun'ts BATT end to it's LOAD end, it's positive. The other way is negative.

I think the CA has enough juice to handle the task if wired & programmed properly.
You can pay Grin to write custom firmware; just talk to them about what you want it to do, and the cost.

The problem you'll encounter is that the CA's MCU only has a few analog inputs, so you would have to sacrifice one of them from it's normal purpose to read the second shunt (like the Aux Pot), and then modify the CA hardware to go with the custom firmware.

Another problem is the MCU also only has so much memory, so the new features would probably require removing others to make room for the code.

You'd have to talk to Grin about the specifics of all of that, when working out the custom deal.


FWIW, there's a relatively simple way to ensure you only ride "solar":

If you have a battery on the BATT end of the shunt, and the solar output on the LOAD end of the shunt, and ride so you always show zero Amps on the current display, then you're riding so that the net power usage is only what is provided by the solar.

If you ride so it shows a negative Amps, then you're letting the solar charge the battery.

If it's positive, then you're exceeding the output of the solar, and using up your battery.

If you also watch the Ah (or more accurately, the Wh), it will keep track of the net usage, which you want to keep to zero or negative. If you see it creeping positive, then you need to reduce power usage until it's not.

billvon
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Re: Solar Cycle Analyst?

Post by billvon » Jan 17, 2018 2:20 pm

the e wind wrote:
Jan 17, 2018 10:29 am
I propose that it would be very useful to purchase a Cycle Analyst that utilizes two shunts; one for solar input, and one for motor output. This way, your bike would be able to accurately display input & output power with one gauge instead of using a second meter.
If you want to have one meter accurately measure the state of the battery, then just connect the solar charge controller downstream of the Cycle Analyst current shunt. That way the CA always shows the state of the battery accurately. Generating more than you use? Then you will see a negative current, as if you were doing regen. Using more than you generate? Then you will see a positive.

If you want a separate display for solar for some reason (not too important, but might be cool) then there are plenty of inline meters that will show that.
you could set the pedal assist level based on how much power you are making.
As mentioned, just tweak it until net power is close to zero.
--bill von

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