Super-Supercaps

[curiouscarbon]

interesting, thanks for sharing

reducing ripple current on the batteries when using inverter is interesting to me

some people place it in parallel with battery

if i added one to reduce current ripple, i'm not sure exactly how to integrate it.

due to such power, i would want to have a way to programmatically isolate it from the circuit

one high amp contactor per pole plus a resistive precharge and bleed off (safe shut down) circuit is one way that i would consider.

 

[FilterGuy]

reducing ripple current on the batteries when using inverter is interesting to me

some people place it in parallel with battery

if i added one to reduce current ripple, i'm not sure exactly how to integrate it.

Placing the s-cap in parallel to the battery and close to the inverter would be how to reduce the ripple current. This is the exact same thing as putting a capacitor across an AC rectified half-wave DC circuit in a power supply. It is a filter that makes the big ripples into small ripples.

The other way to look at it is that the supper capacitor is just adding to the inverter's internal big capacitor bank that is already across the positive and negative inputs.

 

[curiouscarbon]

thank you for helping me understand capacitor integration!

 

[sunshine]

reducing ripple current on the batteries when using inverter is interesting to me

Extending battery life span by reducing micro cycles may be the most beneficial use of super caps.

Placing the s-cap in parallel to the battery and close to the inverter would be how to reduce the ripple current.

Across the battery terminals was how I installed mine
Super Farad Capacitor 16V 83F

(actual 70F according to a negative review that I read before buying)

A better position may be directly across the Inverter terminals on separate cables to the battery's.

Under and over voltages caused by load surges and pwm issues have gone. However this is with very old SLA and the next step
will be seeing if I can disconnect the batteries...maybe after some more super caps.
Larger lithium obviously won't show that amount of improvement.

 

[FilterGuy]

Larger lithium obviously won't show that amount of improvement.

True that. The internal resistance of Lithium is much lower than SLA. It will be much more capable of supplying surge current with minimal voltage sag.

 

[FilterGuy]

Across the battery terminals was how I installed mine

I have no experience with adding a super-cap to a battery system so take my comments with a grain of salt.

I figure putting the additional filtering closer to the source of the ripple would be better.... However, unless the distance between the battery and the inverter is large, any difference between one spot and another is probably marginal at best.

 

[toms]

I use a supercap with my LiFePO4 to prevent AC charge source ripple, and mainly to lower surge current from electrical motor startup.

My system runs a negative and positive busbar. The inverter is connected to the busbar directly, the charge controllers are connected to the busbar via circuit breakers.

The supercap is connected to the busbar via a NH00 slow blow fuse.

The LiFePO4 is connected to the busbar via a LVD contactor, then NH00 fuse.

In practice this works well. under “normal” low voltage conditions the inverter will activate its LVD and the supercap and battery remain connected.

In the event of an individual cell LVD forced by the BMS, the contactor opens, and the inverter pulls the supercap down to its LVD and also shuts down.

For the BMS to reconnect the LVD contactor, a charge source must be present. The supercap is brought to the same voltage as the battery by the charge source before the LVD contactor opens.

When the system is initially commissioned, i use a car battery carbon plate resistor battery tester to connect the LiFePO4 and the supercap until current flow ceases.

I use a normal inverter precharger across the LVD contactor.

The risk with a LiFePO4 battery and a supercap is that you can easily exceed the C rate of the LiFePO4 if you connect a discharged supercap.

In practice this is easy to avoid.

The main reason for my configuration is it allows the discharge C rate of my pack to be minimised. Instead of a surge of 6kw (1.2C) on motor start up, the LiFePO4 now only sees 0.4C.

Essentially enabling me to halve the size of my pack for its intended application.

 

[Hedges]

Me: 'My measurements with a scope indicate most to all of the 60 Hz current draw to feed inverter comes from battery, because no practical capacitor would be large enough.'

How about one of these-
48V 165F Maxwell Super Capacitor 48V 165F Maxwell Super Capacitor 48V 165F MAXWELL SUPER CAPACITOR

If I've done the math right, 5000W inverter 50V battery, 100A draw, 60 Hz half cycle,
165F cap (165 amp-seconds per volt) could supply the current with 0.005V droop.
Lithium battery, 0.25 milliohms/cell 16 cells would have 0.4V droop.

In that case, cap should help smooth out the ripple quite a bit.

"IMPORTANT, 48V supercap will need another 16V in series to make it a 64V super cap. As Caps are rated for their Max working voltage.
A 48v battery sits at 57v or so fully charged. Hence u need 48+16v = 64v."

Great - do they offer a balancer circuit for that?
What we want is a cap we can use with a 48V battery. Might as well DIY with individual caps.

 

[FilterGuy]

"IMPORTANT, 48V supercap will need another 16V in series to make it a 64V super cap. As Caps are rated for their Max working voltage.
A 48v battery sits at 57v or so fully charged. Hence u need 48+16v = 64v."

Capacitance ADDS when wired in parallel but diminishes when the capacitors are wired in series.



Two 70F supercaps in series is equivalent to a single 35F supercap.

 

[Hedges]

It seems they sell a 48V, 165F cap and a 16V, 500F cap.
Probably the came caps inside? Math works out to be within 1%
So put them in series and have a 64V 125F cap.
If they also have same value balance resistors, should still work.

$300 + $150 = $450.
You could use four 16V in series, but 4 x $150 = 600V. Maybe they would give a quantity discount.

"We supply Used Maxwell ( American) Super Capacitors. These are taken off Electric trains after their service life."

 

[sunshine]

Great - do they offer a balancer circuit for that?

Yes.These are ex-electric train capacitators, The full story is here

Super Capacitors

Super Capacitors

www.fpv-power.com.au

There may be similar sources in your region.

New Maxwells were unobtainable and most likely exceed the cost of new LiFePO4

$Farad for $Farad I brought one of these- choice was helped by the negative review, since removed, showing true cap of 70f, they arrived and appear well made.

38.63US $ 20% OFF|Super Farad Capacitor 16v 83f 6pcs 2.7v 500f Flat Angle Electrolytic Capacitor With Protection Board Single Row Ultracapacitor - Filters - AliExpress

Smarter Shopping, Better Living! Aliexpress.com

www.aliexpress.com

 

[MattiFin]

Me: 'My measurements with a scope indicate most to all of the 60 Hz current draw to feed inverter comes from battery, because no practical capacitor would be large enough.'



If I've done the math right, 5000W inverter 50V battery, 100A draw, 60 Hz half cycle,
165F cap (165 amp-seconds per volt) could supply the current with 0.005V droop.
Lithium battery, 0.25 milliohms/cell 16 cells would have 0.4V droop.

In that case, cap should help smooth out the ripple quite a bit.

"IMPORTANT, 48V supercap will need another 16V in series to make it a 64V super cap. As Caps are rated for their Max working voltage.
A 48v battery sits at 57v or so fully charged. Hence u need 48+16v = 64v."

Great - do they offer a balancer circuit for that?
What we want is a cap we can use with a 48V battery. Might as well DIY with individual caps.

You also have to account for the supercap IR (or ESR as it is usually called for capacitors)

Brand spanking new maxwell unit has 6 milliohm ESR.

https://maxwell.com/wp-content/uploads/2021/08/48V_ds_DuraBlue_3000685_4.pdf

"Typical" ~300Ah DIY LFP battery today has 16x0,25 = 4 milliohm IR
Or the Aliexpress module linked by sunshine has 3*6=18 milliohms for 12 volt bank and using same caps for 48v would result 72mOhm ESR

Plate overpotential/starvation and whatnot chemical things going on inside the battery complicate the analysis as it is not just ESR vs IR but the bottom line is that you need very large and expensive supercapacitor to have any effect on LFP battery bank.
In typical home use it is probably not justified as batteries don't see short cycling with very large charge-discharge currents (unlike something like electric bus in city traffic that is constantly between regen braking and accelerating)

 

[toms]

As i explained, with my bore pump / desalination plant battery, the supercap enables me to halve the battery size required to stop exceeding the discharge C rate i’m comfortable with.

It does also completely eliminate AC ripple from AC charge sources.

 

[sunshine]

In typical home use it is probably not justified as batteries don't see short cycling with very large charge-discharge currents (unlike something like electric bus in city traffic that is constantly between regen braking and accelerating)

Is it "batteries don't see short cycling'' or should it be "we don't see the batteries short cycling"
Compare two systems. One with a very small battery capacity and the other with a very large battery capacity.
The small one would have a number of cycles during the day. Maybe not full cycles but rather a number of fractional cycles.
I see a super cap having a very positive outcome for this small battery size.
Less so for the larger bank.

Prior to the addition of the Chinese Super Cap I was considering the purchase of a UPS for the PCs occasional restarts. No longer a problem.

 

[MattiFin]

As i explained, with my bore pump / desalination plant battery, the supercap enables me to halve the battery size required to stop exceeding the discharge C rate i’m comfortable with.

It does also completely eliminate AC ripple from AC charge sources.

You mentioned that battery current went from 1.2C peaks to 0.4C peaks. Measured? Calculated?
What sort of battery and supercapacitor you are using?

 

[toms]

Measured current peak. Sinopoly 100ah cells in 2p16s config. Maxwell Supercap as described in this thread.
(not using the BMS or active balancers shown in this pic)

 

[curiouscarbon]

I use a supercap with my LiFePO4 to prevent AC charge source ripple, and mainly to lower surge current from electrical motor startup.

My system runs a negative and positive busbar. The inverter is connected to the busbar directly, the charge controllers are connected to the busbar via circuit breakers.

The supercap is connected to the busbar via a NH00 slow blow fuse.

The LiFePO4 is connected to the busbar via a LVD contactor, then NH00 fuse.

In practice this works well. under “normal” low voltage conditions the inverter will activate its LVD and the supercap and battery remain connected.

In the event of an individual cell LVD forced by the BMS, the contactor opens, and the inverter pulls the supercap down to its LVD and also shuts down.

For the BMS to reconnect the LVD contactor, a charge source must be present. The supercap is brought to the same voltage as the battery by the charge source before the LVD contactor opens.

When the system is initially commissioned, i use a car battery carbon plate resistor battery tester to connect the LiFePO4 and the supercap until current flow ceases.

I use a normal inverter precharger across the LVD contactor.

The risk with a LiFePO4 battery and a supercap is that you can easily exceed the C rate of the LiFePO4 if you connect a discharged supercap.

In practice this is easy to avoid.

The main reason for my configuration is it allows the discharge C rate of my pack to be minimised. Instead of a surge of 6kw (1.2C) on motor start up, the LiFePO4 now only sees 0.4C.

Essentially enabling me to halve the size of my pack for its intended application.

that’s so cool!

 

[curiouscarbon]

Yes.These are ex-electric train capacitators, The full story is here

Super Capacitors

Super Capacitors

www.fpv-power.com.au

There may be similar sources in your region.

New Maxwells were unobtainable and most likely exceed the cost of new LiFePO4

$Farad for $Farad I brought one of these- choice was helped by the negative review, since removed, showing true cap of 70f, they arrived and appear well made.

38.63US $ 20% OFF|Super Farad Capacitor 16v 83f 6pcs 2.7v 500f Flat Angle Electrolytic Capacitor With Protection Board Single Row Ultracapacitor - Filters - AliExpress

Smarter Shopping, Better Living! Aliexpress.com

www.aliexpress.com

thank you for posting this, very interesting. maxwell big name, cool to use a decommissioned train equipment ?

i’ve wanted to do small capacitor tests to get towards something like what toms described. thanks for the two leads on hopeful sources

 

[Don B. Cilly]

This is really quite fascinating.
For a layman like me - not quite in terms of electronics, I understand capacitance and Farads - would there be a way to... equate, not quite convert, hundreds of Farads (hey, huge numbers, if you're used to micro and milli at best) to Ah?

I mean (just curious mind you) if you had a big enough supercap, or a bunch of them, maybe with a shunt on the "output" to limit current, could it replace a battery?
And would it have "infinite" cycles - for its lifespan, which could be considerable if properly sized?

 

[sunshine]

I mean (just curious mind you) if you had a big enough supercap, or a bunch of them, maybe with a shunt on the "output" to limit current, could it replace a battery?

From this interesting video on YT ' Supercaps do MW/sec Batteries do KW/hr'

& with a nice view of Estonia.

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