Batteries and New Battery Technologies

Hallelujah :!: Some knowledgable battery discussions. Just what I had hoped for with the start of this subject thread. Please keep up the excellent work gentleman.

 

Very good point about the recharge stations. Even current battery technology struggles with the power available from domestic supplies when charging. A friend has an electric car, a Berlingo van, and he finds that it runs close to the maximum current that his household 240 volt supply can deliver, and even then takes several hours to charge.

I'm afraid I've no experience with zinc/air cells, other than having read some of the literature. The idea of using some form of recyclable zinc pellet fuel system seems attractive, at least from the possible ease of "refuelling" perspective. I'm not sure if this technology will make it to the market, though, as there seems to be a greater push in other directions.

Jeremy

 

As you probably know, obtaining a stable voltage from a variable source is done with a switch mode power supply. This is readily available technology for power demands up to several Kw. The DC/AC converters on the market now can run on input voltages with a + and - 40% margin and could even do better if there was no battery protection circuit built in.

If the input came from a capacitor there is no need to switch off when the input voltage drops below a certain point. Also, the input voltage could be chosen freely as long as the MOSFET's for that voltage can be cheaply produced.

Much larger currents are required for electric vehicles, but also that technology is on the market. I weld with an electronic "transformer" that can be adjusted from 20 to 120 Amps with a single knob, has 100% reliable short circuit current limiting and a superimposed 4 Kv to start the welding arc. The whole package, with gas valves and plasma cutting torch costs 220 euro!

 

As I recall, welding voltages are in the order of 40v or so? That would be 40 X 120 = 4800 watts/ 750 = 6 horsepower, not enough for the smallest auto. Correct me if I'm overlooking something, or missed your point.

Also, everything is on hold until the issue of fast recharging technology for electric autos is found. The best fast charging I know of is called "dump" charging used in electric vehicle drag racing lasting a few minutes. The rapid refueling "dump" is made from a huge bank of stationary batteries that have to be slowly charged over hours at the maximum electric service available. That's just to refuel one racer. Can't see how the typical petrol station scenario (with repeated simultaneous fast fueling) could be done. Also there is a great loss in efficiency with dump charging because of conversion from electrical to chemical stored energy.
But, hey, I could be wrong. Just explain it to me.

One thing I wonder about with supercaps is how efficient they are in storage of electrical energy aside from their self discharge losses?

Porta

 

I'm certainly not arguing that the technology to make capacitor energy storage viable is impossible to implement, just that it's overly complex for use in a consumer product, like a boat or vehicle.

I'm currently developing an electric inland waterway boat, and three things are driving my thinking. First is suitability for the "mission profile" (how well does it fit the user requirements), second is efficiency (how simple and cheap is it to build and run), third is reliability (how long will it operate within the design limits without the need for maintenance and repair).

My major concern with any energy storage system that requires complex management systems (be they BMS systems or switched mode converters) is the possible compromise to items two and three in the above list.

I would love to push the technology boundaries with electric propulsion systems for boats, but I'm also very aware of the real-world environment in which such systems will be used. This makes me cautious when it comes to adopting relatively unproven technologies, particularly when lives might depend on reliability and easy repairability in difficult conditions.

Jeremy

 

Quite some energy

Hi Jeremy,

I am not so concerned about the reliability of a capacitor. A capacitor in various shape, size and material is with us already for a long time. I am more worried in the event of a short because of seawater touching both terminals. Can you imagen 100.000 Farad being short circuit by a leak? For that reason I was looking at 2 pontoins wherein the batteries are located. (refer thread : trailable electric catamaran) If the terminal does become under seawater, at least I have a chance in the middle part (or so I am trying to think so, maybe I get blown with it in the air. Will let you know when I try it out)

You are very well right that unproven technology must be handled with caution. But the same will apply to electric cars in an accident. How will that 100Kwh battery be protected from not releasing such enormous energy?

I personnaly think that the recharging will have to be done over a periode of time, let say you go for a cup of coffee or for lunch, while your car is being recharged. Most likely more planning on/for a long distance trip will have to take place. This 10000 Ampere in a few seconds will not be the right solution in my view.
BertKu

 

It's not the capacitor reliability that worries me, Bertku, it's the complexity of the additional circuitry that is needed to deliver useful power to a motor. In my experience, electronic systems and water make uneasy bedfellows.

Jeremy

 

Bertku......post 251 ..total technical cock up here ...there are only negative electrons .....where did the positive ones come from ??? If your wife has a Msc in chemistry she can sort you out on this one ....... a major technical slip like this make everyone think twice about the validity of what you write

 

This is my experience also, especially around saltwater atmosphere which seems to condense and wick in everywhere. So that's a concern with electronics necessarily packaged with Li batteries as well. Also with commercial troll motors that have PWM speed control, which used to have higher failure rates.

So I've only used resistance speed control types, which are cheaper and simpler anyway. A bonus with these 5 speed types was that you can easily "turbo" power to double the rated thrust. This is done with resistance type motors simply by doubling the voltage going in and using a smaller or lower pitch prop, in such a way that the rated current design is not exceeded. This was years back when all mass produced troll motors used brushes.

Porta

 

PORTA whats a resistance motor ??? new design ? invention ??
If you double the voltage but keep the current down to the original level you still dissipate twice the power P = V x I ...... V doubles so P doubles ...so the motor is still overloaded...you have increased the revs and hence the back EMF but the power dissipated is still twice rating.

 

Resistors put in series with a motor bleed off current to control speed.

Yes, twice the power at twice the rpm, that's the beauty of it. Not overloaded because the prop pitch is cut back so the motor is significantly idled. No additional heat in the wiring because it is thick enough to handle the design current. Very low 1800 rpm at 12v goes to 3600 at 24v or less loaded down. 3600 is not enough to throw off armature coils. I discovered this when I noticed the motors minn kota was using were identical for the two models, and only the prop was different!

Porta

 

resitors in series do not bleed off current ? where is it bled to ?
Resistors in series waste your battery power as heat which is why a PWM controller with MOSFETS is more efficient
So what you are now saying is that in one application the motor was under run and could run at twice the power dissipation without problems ....
good now we got that technically correct .....

 

Yes, you are absolutely correct, PWM is more efficient at any lower speed, except half speed if you were running through a series-parallel switch like I was. But it is LESS efficient than a half and full speed switch, because it draws a very small amount of power unless it has a bypass. In my applications, troll motors were so underpowered that I only used full speed except when accelerating or slowing down, which was maybe 5%? of the time, and I didn't go thru the resistors much. You can also control speed more efficiently than PWM by switching out to calibrated propellers should you need to go at a slower speed. Of course this is not practical, unless you have a variable pitch prop that can be remotely adjusted. Does that sound right, or am I going wrong somewhere?

The "underpowered" motor was the highest power they had for many, many years, then they came out with the "new" super thrust at 4X the price. They were not "under running" AFAIK, because they were trying to get maximum thrust using a large, aggressive prop. Efficiency is higher at lower rpms and with larger props is my experience. Anyway, the voltage range possible with brushed motors has come in handy for many situations. Sometimes the best prices are on battery packs that are for those over my rated voltage, so I just adjust with a different prop. http://www.amazon.com/gp/product/B000JTBPF6 Other times they have provided a limp home mode at lower voltages by switching props.
If there are errors or misrepresentations, let me know. Indeed, I hope this has been helpful.

Porta

 

Electrons

Hi Pistnbroke,

If you have two plates with a dialectricum between them and you connect the two plates to a Voltage potential. Let say one side to a plus 24 Volt battery or a battery charger and the other side to the negative, due to the potential difference, the negative plate obtain more electrons (It is being loaded from the battery or charger) and the postive part looses electrons. Therefore the myth that the current flows from plus to minus is actual that the electrons flow back from minus to plus, if discharged via a resistor or motor or lamp when connected to such capacitor. (If you remove the capacitor and put the lamp etc onto the terminals of the capacitor) Don't worry Pistnbroke, I also had difficulties with that when I did my studies. I hope that I have explained this in an understandable way.

BertKu

 

Well you made a better attempt but still got it wrong ...and its dielectric by the way .....when the battery is connected to the plates electrons are removed from the one conncted to the positive terminal and are pushed throught the battery onto the negative plate ....positive plate looses electrons negative plate gains electrons ........when you discharge the electrons run back through the load to the positive plate .....yes I know the french scientist Du fay got it wrong ..but the french stuff everything up ....concorde ..diana ..Brazilian jet ......

I never had any proplems with electrics/electronics when I did my degrees ....I am trying to put you right .........(_!_)

You did still not explain about the positive electrons ....