EEVblog Electronics Community Forum
Electronics => Beginners => Topic started by: JacquesBBB on August 28, 2017, 05:29:22 pm
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I have seen several videos on the net showing a bank of supercapacitors to start a vehicle.
I decided to try and to replace the faulty battery of my husqvarna CTH 150 lawn mower
with a band of 6 Maxwell 2.7V 350F cells, gathered with a regulating PCB similar to this one
http://www.ebay.com/itm/1pc-Six-In-Series-MaxWell-2-7V-350F-T11-Super-Capacitor-Balance-Protection-Board-/282514839318?hash=item41c7325716:g:NssAAOSw9ytZnUG- (http://www.ebay.com/itm/1pc-Six-In-Series-MaxWell-2-7V-350F-T11-Super-Capacitor-Balance-Protection-Board-/282514839318?hash=item41c7325716:g:NssAAOSw9ytZnUG-)
I charged it to 14 V. It seems to start but was not sufficient to start my mower.
Of course, the voltage drops rapidly, and you do not have many tries before you need to charge again the supercapacitors.
I suspect that the delivered current is not large enough but I had no mean to test it properly.
Does anyone has some experience on these supercapacitor boards ?
Thanks
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It probably provides enough current, just not for long enough to start the engine. The battery stores much more energy than the capacitors, which also will have around half the energy left in them, assuming the motor stops turning, when the voltage drops below around 10V.
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I couldn't resist.. https://www.youtube.com/watch?v=tKki89sq0XY (https://www.youtube.com/watch?v=tKki89sq0XY)
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Check member Psi's posts on supercaps........easy to find with a search.
When faced with the same problem i said, "screw it" and put the caps into the car without any protection, balancing or SLA :-DD
(http://psi.abcom.co.nz/supercapcar.jpg)
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that was painful to watch
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I couldn't resist.. https://www.youtube.com/watch?v=tKki89sq0XY (https://www.youtube.com/watch?v=tKki89sq0XY)
That scope does current measurements (3:38)... What?
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I couldn't resist..
That scope does current measurements (3:38)... What?
No, he has a current probe hooked up on his scope.
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No, he has a current probe hooked up on his scope.
How does that change the measuring of current on his scope? The scope even shows the proper current readings.
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No, he has a current probe hooked up on his scope.
How does that change the measuring of current on his scope? The scope even shows the proper current readings.
This scope allows user to set Y-scale units to amps and define the volts/A ratio (transresistance) to define the scale. But the scope still measures only voltage.
Regards,
Janne
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It might be nice to see whats inside one of these, they are stated as using supercapacitors.
Sealey E/START800 ElectroStart® Batteryless Power Start 800A
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This scope allows user to set Y-scale units to amps and define the volts/A ratio (transresistance) to define the scale. But the scope still measures only voltage.
Regards,
Janne
What would you consider actually measuring current? As long as you can somewhat accurately deduce something, you're measuring it.
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This scope allows user to set Y-scale units to amps and define the volts/A ratio (transresistance) to define the scale. But the scope still measures only voltage.
Regards,
Janne
What would you consider actually measuring current? As long as you can somewhat accurately deduce something, you're measuring it.
The combination of a scope and a current probe is something which can be used to measure current. I'd consider something that could be used to flow current through it so that the current gets measured by some method and the result then displayed appropriately to be able to measure current. Scope itself is not very good at it without the current probe.
Of course one could say that 1 M\$\Omega\$ input resistance (or 10 M\$\Omega\$ with 1:10 probe) in a typical scope could be considered as a current measurement shunt for small (or huge depending who you ask) currents (conversion factors of 1 V/µA or 10 V/µA). But for many "usual" applications, that is way too high value for a current shunt. Somewhat philosophical question but this is how I generally see this.
Regards,
Janne
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The issues with supercaps vs chemical batteries is one of the voltage vs energy content profile.
A battery, does have some capacitance, but the vast majority of it's energy is released from a chemical reaction. So, as you take power from it, it's output voltage stays fairly high. (of course, it has some effective internal resistance, so the output voltage you see does fall as current increases)
A super capacitor stores electrons directly. Take some out of the cap and there are less left inside to bounce around and produce a voltage. So as you drain the energy, the voltage falls. Most modern cars require around 8 volts at a minimum for their electronics to function, fall below this, and you can crank the engine as much as you like, but it ain't going to fire up!
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A few years back I also built a super capacitor bank of 6 x 350F in series and tested the ability to start an engine.
It works well on a good starting small engine.
A small Toyota engine for instance, turned on every time
A larger V8 truck engine did not start up at all.
One of the problems is the voltage drop with the PCB at these capacitors.
At 500A, the voltage drop at every small resistance becomes significantly large.
A second test I did with larger super capacitors with threaded connectors, I think it was M12 thread.
I made bride connectors out of solid copper, to keep any voltage drop to a minimum.
This made a huge difference and even the V8 truck engine started up.
If it comes to measuring the current, I found that most current probes are far too slow for the task.
So the best way to measure the current with a scope was to use the voltage drop of the main cable from the +Capacitor to the starter motor.
I should have my scope pictures stored somewhere and will look for them.
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Thanks HighVoltage,
That was the kind of comments and testimony I was looking for.
There are plenty of Youtube video, but they do not necessary show the problems you can encounter when
trying to do the stuff.
I have not my board on hand, but this week end, I will try again after adding thick copper wires
to the main traces of the PCB.
I initially added some solder, but this may not have been sufficient.
I can also try to measure the current and/or the voltage with a scope and
a current probe like this one
https://www.aliexpress.com/item/1pcs-Brand-New-High-Quality-30A-SCT-013-030-Non-invasive-AC-current-sensor-Split-Core/32715724000.html?spm=a2g0s.9042311.0.0.DaJtL0 (https://www.aliexpress.com/item/1pcs-Brand-New-High-Quality-30A-SCT-013-030-Non-invasive-AC-current-sensor-Split-Core/32715724000.html?spm=a2g0s.9042311.0.0.DaJtL0)
Although this may only be used with AC ?
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Youtube creator ElectroBOOM has a video on starting a car with supercapacitors. He shows using a oscilloscope to measure the voltage and current during the starting process.
Just search on "Cranking a Car with Super Capacitors (Supercap)"
As you can see, Cliff Matthews has already posted the video of Mr. Electroboom above. ;)
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I have seen several videos on the net showing a bank of supercapacitors to start a vehicle.
I decided to try and to replace the faulty battery of my husqvarna CTH 150 lawn mower
with a band of 6 Maxwell 2.7V 350F cells, gathered with a regulating PCB similar to this one
http://www.ebay.com/itm/1pc-Six-In-Series-MaxWell-2-7V-350F-T11-Super-Capacitor-Balance-Protection-Board-/282514839318?hash=item41c7325716:g:NssAAOSw9ytZnUG- (http://www.ebay.com/itm/1pc-Six-In-Series-MaxWell-2-7V-350F-T11-Super-Capacitor-Balance-Protection-Board-/282514839318?hash=item41c7325716:g:NssAAOSw9ytZnUG-)
I charged it to 14 V. It seems to start but was not sufficient to start my mower.
Of course, the voltage drops rapidly, and you do not have many tries before you need to charge again the supercapacitors.
I suspect that the delivered current is not large enough but I had no mean to test it properly.
Does anyone has some experience on these supercapacitor boards ?
Thanks
6 of those caps in series is 350F/6 = 58F
Under, say 100A mower start current, that will drop at 100A/58F = 1.72V per second.
So, assuming it takes 2 seconds to start your mower that will be 3.44V lower than start voltage after 2 seconds.
So your 14V super caps are now 10.56V.
I would have expected that to start the mower ok. but it is dropping quite fast.
My guess is that your wires to the caps are not thick enough and your dropping voltage due to cable loss.
Also check how you are connecting each cap to the next, maybe the link has too much resistance which is dropping voltage. That PCB doesn't look to have thick enough traces to handle 100A. Maybe add some solder/wire to the traces to thicken them up