Ultracapacitors parallel to houe battery.

[Frode]

Originally Posted by stevensuf

Anyone think there is any truth in it? they are cheap enough nowadays? worth an experiment?

If you like to discover your own facts, in a world that's overrun with conjecture, assumptions, and lies, it is absolutely worthwhile to do an experiment.

I decided years ago to build start modules based on Maxwell's BoostCap 3000 supercapacitors, connected six in series. Huge difference when compared with the aging Lifeline 8Ds, which dropped their voltage to below 10V as soon as the starter engaged.

However, after upgrading the house bank to 12kWh of lithium iron, and with 4/0 cables already running from house battery location to each engine compartment, the start modules now are mostly superfluous, as the LiFePO4 batteries can crank these engines for a long time (mine take less than 1 second to kick over, anyway).

The added positive effect of having energy near a huge power drain, such as a windlass, even on a DC-Bus system like mine, can be accomplished by other approaches. For instance, an inrush current limiter for refrigeration compressors entirely removes the massive spike at start-up.

If you wire up your ultracapacitors the way Maxwell builds its own start modules, where there is a third post on the module that connects to your DC system, it can charge itself fully, even if the source voltage is as low as 10V, thereby providing starting power when the house battery capacity is mostly gone (not an issue for us litium users).

[skenn_ie]

You need some electronics between the capacitors and the rest. Batteries, during the bulk charge/discharge phase doesn't change voltage by much. Capacitor's voltage is very closely coupled to charge state/stored energy. Electronics (DC-DC converter) convert capacitor voltage to battery voltage, regardless (withing reason) of capacitor charge state.

[Frode]

Originally Posted by skenn_ie

You need some electronics between the capacitors and the rest. Batteries, during the bulk charge/discharge phase doesn't change voltage by much. Capacitor's voltage is very closely coupled to charge state/stored energy. Electronics (DC-DC converter) convert capacitor voltage to battery voltage, regardless (withing reason) of capacitor charge state.

This is absolutely correct, but I have found it is of little practical importance that the UC's voltage drops quickly when discharging. Cranking an engine at 10V works great, when the current is available, which it is when using a UC-based start module, but is not when using a LA battery. It's a similar scenario for other DC motors, as they turn happily at lower voltages, with adequate current.

[a64pilot]

We started the Auxiliary power unit on the AH-64 hydraulically, using an accumulator charged up to 3000 PSI.
Pretty much a mechanical capacitor, what is noteworthy though is if the APU didn’t start, that meant you had to get out and with about a 3 ft pump handle you had to pump the accumulator back up to 3000 PSI for another attempt
If you starting power is coming from a capacitor bank, how are you going to pump that back up?
If your answer is from batteries, what’s the need of a capacitor bank?

From a very high performance perspective for a vehicle that needs to be self starting, I can see maybe a capacitor bank saving some weight.

However I can assure you that my several hundred pound battery bank can spin my little 40 HP 2.5L baby Diesel until the starter burns up, and still have lots of power left.
If your bank of batteries really drops to 10V then something is wrong, I’ve not measured my drop but I’m sure I don’t get an almost 3V drop at the batteries, at the starter due to wiring size maybe.
However any small single battery will easily start my little engine with no problem, why would you want to complicate things by adding in a capacitor bank?

Finally of course the people selling them will tell you they will make your battery last longer, I’m surprised they don’t calm better fuel mileage and an increase in HP too.

[Frode]

Originally Posted by a64pilot

If you starting power is coming from a capacitor bank, how are you going to pump that back up? If your answer is from batteries, what’s the need of a capacitor bank?

Ahh, but there's one of the sweet things about the capacitor. Imagine, in your pneumatic starter scenario, you had a small air compressor, running off of any battery voltage, that would take the manual labor element out of it. Eventually, your 3,000 PSI pressure would be back up, and you could start the engine.

I can, very easily and inexpensively, charge a capacitor start module up to 16.2 volt (specs of 2.7V max per capacitor) from any battery voltage. So, regardless of what the voltage of the house bank is, as long as there is some amount of extractable energy left in it, the start module can be charged, and you can crank the engine.

Many of us have experienced old LA batteries having nowhere near cranking power in the morning, after what we thought was a reasonable amount of consumption during the night. The capacitor start module can overcome such a scenario.

We must be careful about judging the value of an implementation based on how we envision it affecting our own specific setup. For someone who has, like me, a huge bank of lithium ion batteries, this type of start module has limited value. For others, it may just be what saves your bacon in an otherwise difficult situation.

[Robert Jansen]

Years (actually decades) ago, I had an interesting conversation with a couple of electrical engineers who were working on improving the starting effiicency of electrical motors. Their solution was simple and effective: quadruple the size of the starting capacitors. The motors in question were simple single phase AC with starting and running windings, so I do not know if the solution is directly applicable, but it would appear that the use of ultracapacitors to improve the inrush current profile in the starting cycle is sound, at least in principle. However, like anything else electrical and/or electronic in nature, the devil is going to be in the details.

[sdj]

Originally Posted by a64pilot

They are sold very often to people who put together car stereo’s that just make noise, in other words very high power bass producers, not music.

They are snake oil as a battery is in effect one truly massive capacitor.
You would be much, much better off adding another battery.
Plus I believe caps discharge is extremely short, like a strobe, things lie starters and windlasses etc are much longer duration.

My opinion of course

Your mostly incorrect opinion stated as fact.

There is a very good reason to add a stiffening capacitor to a subwoofer system, and that reason is equally applicable to engine starting systems.

Yes, a supercap would stiffen the battery up substantially, but there's really any reason to do that.

[senormechanico]

One thing to consider that has not been mentioned.
The capacitance is divided by putting multiples in series to achieve a working voltage.
If you start with for instance a 2 volt rated 1 farad capacitor and put 7 in series to achieve a 14 volt working voltage capacitor, your capacitance is now 1/7 of 1 farad, or 0.143 farads.

[a64pilot]

I guess your not seeing my point.
Yes if for some reason you wanted to start your really big Diesel off of a lawnmower battery, Caps would allow that to happen, similar in effect as to how a camera flash operates.
However we do just the opposite, we start little bitty Diesels with large battery banks.
Why is it do you think that factory automobiles don’t come with itty bitty batteries and a bank of capacitors?
Toyota, Mercedes and Porsche just done “get it”?
I know it’s becomes they own battery factories right and it’s a conspiracy isn’t it?

Just because you can do something doesn’t mean it makes sense.
You can put a large windmill on a Catamaran and sail directly into the wind, solves that Cats can’t go to windward problem, why don’t you see them?

Ever heard of a Rube Goldberg contraption?

[Frode]

Originally Posted by a64pilot

... we do just the opposite, we start little bitty Diesels with large battery banks.

Your post seems a bit like you're simply trolling, which should be discouraged through not engaging. However, I'll engage, this time, since I'm not sure of your intent.

My 175 HP Yanmar engines (2.5kW starter) have an inrush current just over 1,000 amps. Doesn't last but for a fractional second, before dropping down to a manageable 200 amps or so, but still represents more than what a worn-out or heavily stratified LA battery can handle, even if it's a start battery, not a deep cycle one.

A capacitor-based start module can recharge in about 5-8 minutes, has an estimated lifespan of 10 years (before dropping more than 20% of its initial capacity), and can handle a million charge/discharge cycles. While this solution may not be for you, it shouldn't take too much imagination to see how it could be very valuable for someone else.

Sure, if your batteries are in good condition, with plenty of cranking amps, your cables between battery and starter are of good quality, and your engines start with minimal cranking, you don't need something like this. Is this the scenario for all readers of this forum?

Look for testimonials from truckers on why they want a solution like this, and how they feel about it once they get one.

[Gerrit Coetzee]

Originally Posted by stevensuf

I was just watching a video on ultracapacitors, the guy had replaced his start battery in his car with a capacitor bank, but also was using them in parallel with his house batteries , the reason being they help with high start loads, eg motors etc when running his inverter, reasoning it was extending his battery life by a fair extent by reducing damage done by high demand loads.



Anyone think there is any truth in it? they are cheap enough nowadays? worth an experiment?

The other advantage is that Supercapacitors can be recharged in seconds. New technology allows each capacitor within the bank to give off only a small amount of the stored energy equal to the demand, thus extending battery life and curbing the immediate all power gone scenario.
Trains in China utilises this, with the advantage of recharging the batteries within 10sec between station stops.

The more people buy, use and explore the possibilities in field applications, the more solutions will emerge.
Thus, if you wish to do so and can afford to do so, please pioneer the way and report on your findings. Will eagerly await your results.

[Harry2208]

Some snowmobile manufacturers have gotten rid of the start battery and use capacitor to start. lighter

[alaskanviking]

Originally Posted by redneckrob

Not sure if you didn't read my post just 3 posts above yours or you simply don't believe me? Capacitors don't deliver constant voltage until they are empty! That is one of their biggest weaknesses, they only deliver the voltage they've been charged to for a tiny fraction of their capacity, then the voltage falls exponentially. Take a look at

https://binaryupdates.com/how-capaci...t-and-voltage/ to see this graphically.

I read it. It's not that I don't believe you either. I saw the youtubers playing with this stuff doing that very thing. Running lights ect untill the capacitor discharged. With the increase of electric cars I have seen they are further researching this aspect.

With a grain of salt, the youtubers are mostly playing around with the stuff. I haven't seen anyone doing any practical real life testing of running solely off of a capacitor instead of a battery.

[alaskanviking]

I've been messing with some large ac motors lately, recognised the easy start system is just a bunch of capacitors set up exactly like we have been talking here.

They level out that motor starting current that can be up to triple the amount of normal currant draw

Realized that's exactly what they would do for a starter motor. However thinking on practicality a capacitor bank has some advantages for us boaters. Keeping that current surge low means your corroded and neglected cables don't get as hot, and the surge doesn't mess with the rest of your electrical system. For lead acid it completely makes sense as a buffer to even out the battery voltage from use and charging. Lithium banks won't nessesarily need this aspect. In theory it would prevent any contact scorching from high lithium current flows when you engage the starter. For lithium I think the benefit would be replacing the start battery completely and use the lithium bank for everything. Would simplify your system a little.

For all battery types I think the emergency aspects are the most attractive. As your lead acid batteries get low the capacitors will give full juice. You can really drain the batteries trying to start a stubborn diesel when it's cold out. With Lithium banks you can have issues that will shut down the whole battery depending on the BMS. A capacitor bank would let you still start the engine.

Prices would have to come down for this to be practical, or you have to be willing to diy and out your own stuff together.

[alanfw]

Sorry for reviving this old thread, but it's probably the closest I've found to covering the info I'm looking for.

One of my LA batteries died recently, and I had been considering lithium for quite a while. I replaced the dead battery with a 140Ah lithium house battery and kept the remaining LA battery as a start battery (adding a DC-DC between the LA and Li batteries).

Ideally, I would have liked to get 2 Li house batteries, but there wasn't sufficient room in the battery compartment for two house batteries AND a start battery. I thought about doing away with the LA battery completely, but the Li BMS only has 200A peak (5second) current rating. I expect that starting my 24HP Bukh would cause the BMS to shut down. Ideally, placing two of these in parallel would provide 400A peak, but that assumes perfectly balanced connection, so I'm still very reluctant to do away with the LA start battery. I've been thinking a supercap COULD solve the problem, providing the short current burst - the supercap could be placed in/near the engine room, leaving the space I want for two 140AH batteries.

Have any of the contributors to this thread gone ahead with trialing such a setup? My biggest concerns are:

1. Safety in the case of accidental shorts
2. How to connect the house batteries to the supercap in such a way that excessive surges are avoided and the supercap is kept charged (I know supercaps can maintain charge for a LONG time, but I wouldn't be surprised if there were sources of leakage that would drain the supercap if left without connection to a charge source).