Super capacitors for starting, bowthruster, and windlass circuits

[AKA-None]

Originally Posted by markcouz

Go for it, but just read the Cap spec in my post carefully, note that the F (Farads) and not uF (micro Farads) wasn't a typo!

They are each the size of a deodorant can with bonus filling, the experiment cost me around $600 and I shed a tear when I called it quits.

And they are dangerous to boot
Eg they can dump their charge quickly

[Jammer]

Some interesting stuff upthread.

Supercaps have been available and have been improving in price, performance, and longevity for several decades now. They are now used "more often than rarely" in engine starting applications in environments where FLA batteries are short lived or unreliable particularly regions with extremely hot weather (-> FLAs are short lived) or extremely cold weather (-> FLAs perform poorly).

The correct way to wire these things is to wire them straight to the solenoid but have some sort of current limiting device between them and whatever charge source is being used. This can be as simple as a resistor, a diode, and a fuse in series or could be any of the many current-limited DC-DC converters on the market.

They are not materially more dangerous than FLAs or LiFePO4 batteries on the discharge current side because their performance is limited by ESR, With a properly sized cap bank (i.e. one you can afford) the peak output current is going to be roughly similar to that from a new, fully charged AGM, perhaps less. And there's the advantage that the current will drop after a second or so, which is not the case with batteries. I've seen FLA shorts in starting circuits. It's bad.

I don't know whether the supercaps under discussion are safe or reliable. There are preassembled supercap assemblies intended for marine engine starting applications, but they are expensive for what they are. There are also general-purpose supercap banks from reputable suppliers that can be assembled into engine starting systems with care and expertise.

On wire size, any component-level supercap is going to have small leads and terminals compared to the typical 1/0-4/0 diesel engine starter wiring. There are going to be losses in them and heat that have to be accounted for in the design of the bank. They have to be combined together and fastened physically and electrically to suitable terminals for the larger 1/0-4/0 cable. All that is part of what you are paying for with the more expensive application-specific assemblies.

Digikey, Mouser, etc. all have supercaps and banks for sale from reputable sources with specs and a warranty and so on. They are not prohibitively expensive.

[RaymondR]

I can perceive a use for them where battery storage is a long way from the point of current use, such as an anchor winch where the use is intermittent and the recharge time available extended.

[Jammer]

They don't store enough energy for a windlass, at least in sizes normal people can afford.


The use case is engine cranking. You can store enough energy to crank an engine for, say, six seconds, and recharge the supercaps over the course of a few minutes at 5 amps. Properly engineered supercap banks will last for 25 years. They can replace a dedicated start battery, reduce the amount of 4/0 cable you need, and keep you inside the preferred max discharge envelope for a midsize LFP bank, as noted upthread.

[ngmayo]

Originally Posted by Jammer

Some interesting stuff upthread.

Supercaps have been available and have been improving in price, performance, and longevity for several decades now. They are now used "more often than rarely" in engine starting applications in environments where FLA batteries are short lived or unreliable particularly regions with extremely hot weather (-> FLAs are short lived) or extremely cold weather (-> FLAs perform poorly).

The correct way to wire these things is to wire them straight to the solenoid but have some sort of current limiting device between them and whatever charge source is being used. This can be as simple as a resistor, a diode, and a fuse in series or could be any of the many current-limited DC-DC converters on the market.

They are not materially more dangerous than FLAs or LiFePO4 batteries on the discharge current side because their performance is limited by ESR, With a properly sized cap bank (i.e. one you can afford) the peak output current is going to be roughly similar to that from a new, fully charged AGM, perhaps less. And there's the advantage that the current will drop after a second or so, which is not the case with batteries. I've seen FLA shorts in starting circuits. It's bad.

I don't know whether the supercaps under discussion are safe or reliable. There are preassembled supercap assemblies intended for marine engine starting applications, but they are expensive for what they are. There are also general-purpose supercap banks from reputable suppliers that can be assembled into engine starting systems with care and expertise.

On wire size, any component-level supercap is going to have small leads and terminals compared to the typical 1/0-4/0 diesel engine starter wiring. There are going to be losses in them and heat that have to be accounted for in the design of the bank. They have to be combined together and fastened physically and electrically to suitable terminals for the larger 1/0-4/0 cable. All that is part of what you are paying for with the more expensive application-specific assemblies.

Digikey, Mouser, etc. all have supercaps and banks for sale from reputable sources with specs and a warranty and so on. They are not prohibitively expensive.

My thoughts are a fuse sized to the wire with these devices and not shortcut based on short distances. I'll report my mistakes here in a few months based on the boat setup. All the math says the wiring doesn't have to be 4/0. However, its one of those good feeling things plus allows for a longer delay on the SC curve of the fuse. I'd rather burn a component than a wire in fiberglass if I make a mistake (intent is to not make a mistake and burn either but......).

Also, I just like the idea of having all batteries as house and something in case of an emergency/ overuse for starting the aux diesel and/or generator. Different circuits for Dampening the in-rush on the windlass and thruster will also be without the isolation. I also like the idea of being able to charge a cap from solar, wind, and or non-submerged batteries chemically recharging in a catastrophic event with the hopes of starting a gen or aux diesel (speaking of hope...hope to never experience such events. Also hope to never use an emergency life raft or epirb but.....). Thanks again for the info. Huge help!

[markcouz]

I have attached images of the experimental capacitor bank that I used - the terminals were M8 with 13mm nut so cabling for engine start was not an issue...

[ngmayo]

Originally Posted by markcouz

I have attached images of the experimental capacitor bank that I used - the terminals were M8 with 13mm nut so cabling for engine start was not an issue...

https://www.amazon.com/XJPOWER-Maxwe...9P8JGMHJ&psc=1

$355 with a case delivered. Seems like a heck of a nice starter option when used with a fuse and 13.2 volt isolation solenoid in a LIFEPO4 house battery bank. Essentially less worried about frying/overcharging a AGM. I guess a DC-DC to an AGM is cheaper/simpler, but these seem it will last longer than an AGM for an emergency starting circuit. Now I just have to noodle on unisolated supercaps for LIFePO4 on the thruster/windlass. Probably need to create fused isolatable battery banks (bow and midship) that get charged separately and balanced periodically. Thanks again!

[Nepidae]

It's been my experience that anything 'cheap' on a boat is usually a foreshadowing or portending of serious issues down the river.

Initially, after buying our boat I was always in search of the cheapest guy to do any work on her. I would suspect that the cheapest labor also utilized the cheapest product in doing that work.

Soon I came to realize that I was spending good money to redo the work that the cheapest guy did, including replacing his product.

Be aware that electrical issues are THE most prevalent causes of fires on boats.

My recommendation is to find an ABYC electrician and let that person recommend the capacitors to use in each application. Might cost more, but then what is your boat worth and maybe more importantly, your dock mate will probably appreciate your efforts.

[markcouz]

The Amazon product linked appers to utilise the same Maxwell caps that I used in my experimental setup - 2.7V x 6 = 16V, 6x 3000F caps in series = 500F.

Nothing cheap about those Maxwell caps, they are the best tech available for the job. Dont get scared away by the technophobes!

[dial_amonkey]

t I've also often wondered about these huge inductive loads - like the water pump, windlass, electric winch, bowthruster. I wondered if could use a supercapacator/MOV combo to absorb the back emf and what must be HUGE voltage spikes when these loads are switched on and off. (there doesn't seem to be any protection built in?)

For example: My windlass is powered from the main battery bank and I can hear the fridge hick-up when the voltage plummits from the windlass, or even when the water pump launches. (it's still above the fridge low voltage threshold) - there might be a dip in the milliseconds..that I'm not seeing.

Thinking my batteries might be shot: I measured the internal resistance of the main bank, the wiring and connectors and all seem OK - I have AGM which have a very low internal resistance ~ it's currently sitting in the 10's of milliohms - new might have been closer to single digits.

I've had a couple of circuit breakers die from the voltage arcing across the contacts - but I'm more concerned what these rapid voltage fluctuations do to delicate electronics - as capacitors age they often don't do so well filtering out spikes. The battery should absorb most of the rubbish - but I have not stuck an oscilloscope over it to get a definitive answer ..

[rossdv8]

I trained and worked in Electronics in the 70s, then in the 80s I added Hydraulics, specialising in Ag and Roadworking equipment, and was fascinated by hydraulic accumulators, and always saw them as 'liquid capacitors' in my mind. I was thinking about writing about that analogy, then wondered if there was something onlne that was simpler to explain it than my waffling (for people who don;t have hydraulic OR electronic training).


This might be useful for someone following this thread who doesn't understand capacitors / accumulators:
https://www.brighthubengineering.com...heory-and-use/

[NNBill]

Anyone else worried about the 2.7 volt working voltage on those caps? I hear A BANG in their future. Caps don't like overvoltage.

[markcouz]

Of course this would be a concern, as charging above 16v would be for many electronic components on the boat. If you believe this to be a real possibility then you should take steps to prevent it - e.g. install voltage sensing device to interrupt alternator field wire if voltage exceeds 15V.

[NNBill]

Markcouz. So that we are on the same page, the capacitors in your images and the previous images are rated at 2 POINT 7 (2.7) volts WAY under even the rest voltage of 12 .5ish volts. Thus when building a capacitive dropper LED power supply for a 120 volt LED light, you need a cap rated for a minimum of 170 volts. (120 VAC X 1.414)

[markcouz]

Nope, not even the same book!

The capacitor bank that I built was to start a diesel engine with 24V starter - I used 10 caps in series to give a full charge rating of 27V, I used an MPPT charger to charge the caps to 25V (2.5V per cap).

The Amazon product shown is an engine start cap for a 12V engine with 6 of what I suspect is the same caps that I used - 6 caps in series give a rating of 16.2V, more than enough I believe to accept the 13.8 - 14.4V charge likely to be applied in an engine start application.

These are DC applications, not AC filter/smoothing circuit applications where your cap should be [root2 x rated V] to accommodate peak voltage.