Super Capacitor

[Craig]

Hi Roo, I was just wondering if you did add a supercapicator bank to your system and if so, have you seen a positive impact on your current draw.

I have installed a supercapicator bank on my system and I concluded that it does help out on the power surges, especially for the motor starts, sump pump, furnace fan motor, microwave,. Anyways I'm happy with the improvement. Also current bing drawned from the capacitors is larger at the start of the motor, meaning this current is not drawned from the batteries so saving the amp, in battery storage. It took 6 1/2 months to get the capacitors, they have been installed now for three weeks.

How fast to the supercaps draw from the batteries though. Dont they "drink" fairly fast? I do not know just what I gathered. I have never used one.

 

[Roo]

Yes, I did. I made an experimental unit first to keep it relatively cheap. I've seen setups using capacitors from 100 farads to 3000. The 3000 farad ultra capacitor is quite expensive so I went with 500 farads to see what the result would be.

As I am using 24v batteries I bought 12 x 2.7v 500f capacitors and installed them on 2 x protection boards holding 6 capacitors each. This setup I ran in parallel from battery to inverter. The demand for my well pump is huge, my pressure house pump not so bad. Not really interested in other household devices for this.

I do notice that on pump starts the draw on batteries is significantly less as there's instant access to enough power to start them very quickly.

What this means I'm not sure at this stage. Will my battery bank last longer? Could I use a less expensive inverter? I only bought a large capacity inverter to start the well pump, otherwise it's not required. Difficult to answer these questions without extensive testing.

 

[RCinFLA]

First step is to make sure your battery cabling is sufficent gauge.
Second step is making sure battery voltage is not slumping excessively on surge current. If so, need more battery.
Third step make sure you have large enough AC wire gauge to pump.

Super caps at inverter could help but if only making up for battery cable surge current voltage drop they are an expensive solution.

 

[RCinFLA]

I do notice that on pump starts the draw on batteries is significantly less as there's instant access to enough power to start them very quickly.

Can you explain this statement a bit more?

 

[RCinFLA]

I have a 3/4 HP well pump. A 4 kW, 48v inverter just does start it without too much to spare.

Do you know what the Locked Rotor Amperage (LRA) rating of your pump is?

 

[Roo]

Can you explain this statement a bit more?

I have a volt meter attached to each battery in my bank of 8 batteries. On pump startup the voltage drop is significant. With capacitors installed this doesn't happen as the power is drawn from this source instead of the batteries. Then the batteries take the load of running the pump.

Some people have commented that caps are expensive, a relative point I suppose. I paid $2.00 per 2.7v 500f super capacitor. Ultra capacitors are much more expensive; a 3,000f ultra capacitor is $12.00. In my opinion I don't think this is an expensive add on. To add 1 x battery would cost me $450.00.

 

[RCinFLA]

Some people have commented that caps are expensive, a relative point I suppose. I paid $2.00 per 2.7v 500f super capacitor. Ultra capacitors are much more expensive; a 3,000f ultra capacitor is $12.00. In my opinion I don't think this is an expensive add on. To add 1 x battery would cost me $450.00.

Don't know where you got that price or how long ago it was based on.

Twelve 3000F Maxwell Ultracaps will now cost between $750 - $800. Add to that the price of balancer. That will give you 250F for 24v system with 0.8v drop per sec. at 200 amp draw. (typical induction motor high start current time is 0.4 secs)

Twelve of cheaper 500F is not going to help very much. That is 42F for 24v system with 4.8v per sec drop at 200 amps. I have tried some of the cheap Chinese 500F and their series resistance is 5 to 10 times higher then Maxwell 500F caps making them almost useless.

 

[Hedges]

How fast to the supercaps draw from the batteries though. Dont they "drink" fairly fast? I do not know just what I gathered. I have never used one.

Yes, but you could connect them with a resistor and a diode so they charge slowly but discharge fast.
Induction motors can kick up to speed and starting current surge goes away in just a few 60 Hz line cycles. Starve them for current and the take longer, draw more total power before coming up to speed.
The right capacitor setup, super- or otherwise, could hold up voltage better than a small battery with high internal resistance. I haven't tried.

Inverters have their capacitors too. My Sunny Island, 5750W continuous, are rated 11,000W for 3 seconds. Long enough it is probably using the battery. 229A @ 48V, dropping 10% in 3 seconds would be 143 Farads if capacitor alone. For four cycles, 67 milliseconds, it would be 3 Farads, which may be what the inverter has inside.

Closing a switch into a capacitor will make an unlimited current pulse, hard on the switch. That's why a charging resistor might help.
We had an 0402 sense resistor on a pump circuit for 0.5A, but it kept going open-circuit. With a scope I captured 80A for 10 microseconds due to capacitors on its input. Changing to a pulse-rated resistor fixed the problem.


For the OP, spinning up a smaller induction motor first before the pump might help. The induction motor should push current back into the wire when voltage drops trying to start the pump. I haven't tried it, just theory/SWAG. A "Line Tamer" self-resonant transformer might do the same. Just temporarily hooked to the line (I believe they are lossy), not isolating the pump.

 

[Roo]

Don't know where you got that price or how long ago it was based on.

Twelve 3000F Maxwell Ultracaps will now cost between $750 - $800. Add to that the price of balancer. That will give you 250F for 24v system with 0.8v drop per sec. at 200 amp draw. (typical induction motor high start current time is 0.4 secs)

Twelve of cheaper 500F is not going to help very much. That is 42F for 24v system with 4.8v per sec drop at 200 amps. I have tried some of the cheap Chinese 500F and their series resistance is 5 to 10 times higher then Maxwell 500F caps making them almost useless.

I should point out that the Internet, Websites and Forums such as this are not exclusively U.S.A.-centrtic. We in other continents and countries have had access for some time now.

As of today 29/07/2020 in S.E. Asia, currency exchange puts 3,000f Ultra-caps @ approx. US$150.00 per six pack = $300 for twelve. Prices vary of course on volume. A balancer is so cheap in comparison, not worth any concern.

If the asking price is US$700 - $800 I would strongly suggest looking for another source.

 

[nosys70]

these are not 3000F capacitors, these are 500F capacitors. so you pay 25$ for a 500F capacitor.
But yes from a commercial point of view , 6x500F in parallele makes 3000F.
and the pictures shows Maxwell caps, but the Brand is listed as No brand and the title says "American".
Shady business at least.
it is far from your statement:
" Some people have commented that caps are expensive, a relative point I suppose. I paid $2.00 per 2.7v 500f super capacitor. Ultra capacitors are much more expensive; a 3,000f ultra capacitor is $12.00 "

a xuba 280Ah 24 pack cost less than 1500$.

 

[Denis]

these are not 3000F capacitors, these are 500F capacitors. so you pay 25$ for a 500F capacitor.
But yes from a commercial point of view , 6x500F in parallele makes 3000F.
and the pictures shows Maxwell caps, but the Brand is listed as No brand and the title says "American".
Shady business at least.
it is far from your statement:
" Some people have commented that caps are expensive, a relative point I suppose. I paid $2.00 per 2.7v 500f super capacitor. Ultra capacitors are much more expensive; a 3,000f ultra capacitor is $12.00 "

a xuba 280Ah 24 pack cost less than 1500$.

1 pack of 6, 2.7volt 3000farad capacitor bank in serries will give you a 16 volts 500 farad bank. Capacitors in serries you devide the capacitance by the number of capacitors, and you can buy a bank for around 100$ usd on AliExpress

 

[Roel]

..if you had a full bank of DC superCaps they would not increase the Inverters max surge power.

Would they increase the surge capability of a battery bank and stress it out less if placed in parallel with the batteries?

 

[Craig]

Would they increase the surge capability of a battery bank and stress it out less if placed in parallel with the batteries?

Theoretically yes on the surge capacity. Not sure on stress of bank because the capacitors will want to suck juice from the battery as fast as they can to refill themselves.

 

[theoldwizard1]

This is what I thought I do not know if super Caps can be used as a an AC mechanism. But if you had a full bank of DC superCaps they would not increase the Inverters max surge power.

Sorry for being late to the party, but I believe I do have something to add.

First, what we commonly refer to as "super capacitors" are large capacitance electrolytic capacitors. Being electrolytic, they have polarity and CAN NOT be used (directly) in AC CIRCUITS ! Side note, anyone who as even just glanced at these devices will note that they tend to be low voltage, commonly 2.7V. You would need 6 in series for a 12V application.

Second, when trying to start high load AC devices (pumps, compressors, etc) the issue is limiting "in rush" current. Time for some simple electrical engineering lessons !

Capacitors "resist" change is voltage. When a capacitor is not charged, it will look like a short circuit to a power source, drawing as much current as possible. Adding a large capacitor between a battery and its load (such as an inverter) works, because the battery "looks" like a inifinite current source (for a short period of time).

Inductors (pretty much everything has some inductance), "resist" change in current. Once it is fully "charged", it wants to stay that way and maintain its voltage. Also, when a load is quickly removed, the energy stored in inductor (motor windings, light bulb filament, etc) has to do something with that energy (stored in a magnetic field), so as the field "collapses" it generate a high NEGATIVE voltage spike.

When starting a large inductive load the key is to LIMIT THE IN RUSH CURRENT ! CAPACITORS DO NOT LIMIT THE IN RUSH CURRENT ! What you need is a device that limits current until the load can "ramp up". For AC high inductive loads, something like a MicroAir EasyStart™ 364 Soft Starter will do the job.

 

[Roel]

When starting a large inductive load the key is to LIMIT THE IN RUSH CURRENT ! CAPACITORS DO NOT LIMIT THE IN RUSH CURRENT ! What you need is a device that limits current until the load can "ramp up".

So there is really no point in having a super capacitor in parallel with the battery?

For AC high inductive loads, something like a MicroAir EasyStart™ 364 Soft Starter will do the job.

Interesting unit. What's inside? A large capacitor?

 

[toms]

@theoldwizard1 i agree with what you have said.
I can also say with certainty (having observed it in practice) that having a supercap in parallel with your battery bank will reduce the peak current draw from your batteries.

When a high load is presented, the supercaps and batteries drop voltage together, but most of the initial current comes from the supercap.

There is no residual charge from the batteries back to the supercap - the voltages are locked together. The current is limited by the charge source.

 

[theoldwizard1]

So there is really no point in having a super capacitor in parallel with the battery?

It depends on the size of the battery and the "in rush" current of the load. Typical RV situation. Lets say the battery is at about 50% SOC so about 12.20VDC. The vehicle charging system is working but it has limited power so now the DC system voltage is at 13.2VDC. A load with a large in ruch current comes on line. Without a capacitor the momentary voltage may actually drop below 12VDC ! With a large enough capacitor, it might stay above 13VDC, but only for a short while.

That capacitor is acting as a battery, but only for a very short time.

Interesting unit. What's inside? A large capacitor?

How to make a Softstarter​

 

[theoldwizard1]

@theoldwizard1 i agree with what you have said.
I can also say with certainty (having observed it in practice) that having a supercap in parallel with your battery bank will reduce the peak current draw from your batteries.

When a high load is presented, the supercaps and batteries drop voltage together, but most of the initial current comes from the supercap.

There is no residual charge from the batteries back to the supercap - the voltages are locked together. The current is limited by the charge source.

Total agreement !

 

[Hedges]

So there is really no point in having a super capacitor in parallel with the battery?

Interesting unit. What's inside? A large capacitor?

EasyStart™ 364 Soft Starter

EasyStart™ single phase soft starter lets you start your A/C without buying a second or bigger generator or inverter & run 2 air conditioners on a 30-Amp cord.

www.microair.net

Says it reduces startup current by 2/3 or 3/4, which could really help.

If the load looks mostly inductive at start (current draw almost 90 degrees out of phase, then much of it shoved back into wire), a large capacitor in series would correct that. More likely, chop the signal like a dimmer, limiting max current. That wouldn't help start the motor, probably start even slower but reduce peak current.

Whatever is in that electrical outlet sized box can't be worth near $300.

For less than that I bought a Hitachi 2 HP VFD, which starts a 3-phase motor very gradually. Windings in a 3-phase motor provide the phase shift needed to apply torque (unlike a single phase motor or the pedals on a bicycle, which at one point can't decide which direction it should turn.)

When building an off-grid system you can put in 3-phase 120/208Y. You have 120V legs for smaller appliances, 208 rather than 240V for larger ones, and 3-phase for higher power ones. But VFD still reduce surge to much less, about zero above running current. Only smaller VFD are meant for single phase source, large ones would do better on 3-phase because their capacitor don't have to supply large 60 Hz ripple current.

 

[theoldwizard1]

EasyStart™ 364 Soft Starter

EasyStart™ single phase soft starter lets you start your A/C without buying a second or bigger generator or inverter & run 2 air conditioners on a 30-Amp cord.

www.microair.net

Says it reduces startup current by 2/3 or 3/4, which could really help.

If the load looks mostly inductive at start (current draw almost 90 degrees out of phase, then much of it shoved back into wire), a large capacitor in series would correct that.

All most all motors have a start capacitor. This "looks" like a short circuit when current is first applied. A true "soft starter" limits the amount of current that can feed that short circuit.

More likely, chop the signal like a dimmer, limiting max current. That wouldn't help start the motor, probably start even slower but reduce peak current.

Not sure how that device "limits" the current. It could be a "chopper". It could be as simple as a current limiting resistor that is removed from the circuit (via a relay) a second or two after the current is applied (and the start and run capacitors are now fully "charged"). Yes, the motor will take longer to start. Maybe 4-6 seconds instead of 2-3.

Whatever is in that electrical outlet sized box can't be worth near $300.

Probably not !

For less than that I bought a Hitachi 2 HP VFD, which starts a 3-phase motor very gradually. Windings in a 3-phase motor provide the phase shift needed to apply torque (unlike a single phase motor or the pedals on a bicycle, which at one point can't decide which direction it should turn.)

When building an off-grid system you can put in 3-phase 120/208Y. You have 120V legs for smaller appliances, 208 rather than 240V for larger ones, and 3-phase for higher power ones. But VFD still reduce surge to much less, about zero above running current. Only smaller VFD are meant for single phase source, large ones would do better on 3-phase because their capacitor don't have to supply large 60 Hz ripple current.

You got a steal on that VFD ! Sadly, most "residential" motor are not 3 phase. (I have never seen a 3 phase residential refrigerator or residential A/C, although most residential A/C units will run on 208VAC). While 120/208Y does provide 3 independent single phase outputs, they are at lower current.