Questions/curiosities bout Super Capacitors....

[toms]

That's only true for a very short load spike .... It will if the load is extended.

Kinda seems like you totally changed your opinion from your previous post.

I’m assuming you have been using supercaps in your system for many years like I have. The voltage drops together, a small amount. (If there is no voltage drop there is no current flow). Nothing I said is contradictory, I have been using this system for many years.

If you are still getting significant voltage sag, use a supercap with greater capacity.

The duration of spike support is governed by the size of the supercap. I have posted the specs of my system many times on this and other forums.

 

[Bob B]

I’m assuming you have been using supercaps in your system for many years like I have. The voltage drops together, a small amount. (If there is no voltage drop there is no current flow). Nothing I said is contradictory, I have been using this system for many years.

If you are still getting significant voltage sag, use a supercap with greater capacity.

The duration of spike support is governed by the size of the supercap. I have posted the specs of my system many times on this and other forums.

I'm not using super capacitors .... I'm just discussing the theoretical aspects of the OP's system.

In the post I asked my original question about, you talked about how the charger replenished the capacitor if there was a voltage sag .... now you are saying there isn't a voltage sag ... but, I'm not interested enough to keep going around and around without you answering my original question.

 

[Bob B]

I hope that no one thinks Im arguing with them. I am gratefully digesting and learning from all the input. Any questions i ask are genuine and every answer I get much appreciated.

As I stated earlier, I think you have a good understanding of the theory of how your system is responding.
Sorry if my attempt to clarify things resulted in an argument .... didn't intend to mess up your thread.

 

[toms]

As I stated earlier, I think you have a good understanding of the theory of how your system is responding.
Sorry if my attempt to clarify things resulted in an argument .... didn't intend to mess up your thread.

There is no argument, you are using theory - i am describing actual system operation.

I’m sorry that you interpreted “voltage drop” as “significant voltage sag”.

With my setup of a supercap in parallel with LiFePO4 there is no significant voltage drop under surge load from irrigation pumps / RC Aircon - and no significant current flow from the supercap to the LiFePO4.

That is the answer to your question, and covers what the OP was asking regarding the need for circuitry to protect the battery from high current dump into the supercap during normal operation.

I don’t think you diluted the thread - your view is a good example of what a lot of people think, and gives a good opportunity to reiterate that in practice it is incorrect.

 

[Bob B]

There is no argument, you are using theory - i am describing actual system operation.

I’m sorry that you interpreted “voltage drop” as “significant voltage sag”.

With my setup of a supercap in parallel with LiFePO4 there is no significant voltage drop under surge load from irrigation pumps / RC Aircon - and no significant current flow from the supercap to the LiFePO4.

That is the answer to your question, and covers what the OP was asking regarding the need for circuitry to protect the battery from high current dump into the supercap during normal operation.

I don’t think you diluted the thread - your view is a good example of what a lot of people think, and gives a good opportunity to reiterate that in practice it is incorrect.

YOU are talking about YOUR system .... I am talking about the OP's system .... I'm not going to interfere with this thread any longer in order to get you to understand .... or even admit your own words.

 

[jjchvl]

As I stated earlier, I think you have a good understanding of the theory of how your system is responding.
Sorry if my attempt to clarify things resulted in an argument .... didn't intend to mess up your thread.

No worries! People disagree sometimes. Thats life for sure! Theres lessons to be learned from disagreements as well though, so dont mind me if I listen in.

 

[McKravitts]

You really think a few milliohms difference in battery supply line resistance makes a difference when you have maybe #8 wires to 4 ohm impedance speakers? Reducing speaker driver impedance improves dampening factor on speakers that inhibits speaker cone ringing due to impulse response to bass frequencies, but speaker wires are normally the limiting factor on speaker dampening.

Like gold plated connectors, Monster cables' advertising makes all the difference to auto boomers spending money on their rigs.

The ohms law drops are only a small part of the problem. The main culprits are the response time of batteries and the inductive reactance of the wires from the batteries to the amp.

It is a very measurable drop and if the power to the amp drops the output power to the speakers drops and hence the sound is distorted. It is further complicated by the fact that the distortion is frequency dependent. I've seen the effect on voltmeters and oscilloscopes. Audio buffs are not adding super caps to their systems because it’s a fad. They make a real improvement to the sound quality.
Now, mentally replace the amp with an inverter and the speakers with an electric motor that requires a high starting current and you have a similar issue.
Another issue is the effect on a battery. It is well known that high current draws shorten battery cycle life.
It is also known that low voltage inputs can harm inverters.
The bottom line is that there are a lot of good reasons to consider super caps on solar systems IMHO.

 

[McKravitts]

In practice with a supercap in parallel with LiFePO4 there is no need for a current limiter. You can set up the system so that the charge controller charges the supercap before the battery contactor is closed.

During rapid load application the majority of the current comes from the supercap as the voltage drops. Because the voltage of the LiFePO4 and supercap are still the same they both recharge at the current limit of the charger - there is no current from supercap to battery after initial connection.

You're right toms. The internal impedance of both are so low that the voltages are/have to be equal even under loading. Even after a high current surge the two will be so close in voltage that no harm will come to either. The only issue is during initial installation of the super cap or after any maintanance, repair or addition to the system
The cap should be charged through a resistor to the voltage of the battery bank.

Since many people forget or ignore that step, some manufacturers are now adding current regulators to the caps that only limit current when charging.

 

[Warpspeed]

I do not have any supercaps myself, but I could see some merit of adding a series resistor shunted with a really large diode.

The supercap would charge through the resistor, and then discharge through the diode.
Something like that would be pretty simple and reliable.
Voltage recovery after the dip might be faster too.
I have never tried this, but it might be something worth thinking about.

 

[McKravitts]

I do not have any supercaps myself, but I could see some merit of adding a series resistor shunted with a really large diode.

The supercap would charge through the resistor, and then discharge through the diode.
Something like that would be pretty simple and reliable.
Voltage recovery after the dip might be faster too.
I have never tried this, but it might be something worth thinking about.

What you're describing is basically what some manufactures do.
An FET is often used rather than a diode, since it has a lower voltage drop and charge rate can be moderated.

 

[McKravitts]

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To anyone interested in this topic:
There is a discussion in the Danger zone sub forum this forum: Danger Zone! (Advanced User Experiments Only) forum.
https://diysolarforum.com/threads/u...c-to-supply-inrush-current-on-inverter.47781/
It's a pretty informative discussion with actual solar applications.

Also see: https://diysolarforum.com/threads/super-capacitor-bank-output.44323/