Batteries and New Battery Technologies

I have a couple of the Turnigy motors and they have impressive performance to weight. However their rating is way beyond what you could pull for any reasonable time. Also, as you point out, they rely on rapid air flow for cooling.

If you look at the gear that Kelly controls is offering it is robust. The ratings are continuous and the controllers can be programmed for a particular application. There is a slight weight penalty but it is small when considering a boat application.

I have little doubt my Mars motors will push out 1 to 2kW for a very long time without bearing or magnet problems. They give better efficiency than any of the RC stuff.

I started thinking about what I would use for a lightweight outboard that would not require constant nursing. The RC stuff is just too finicky for this application.

Rick W

 

Rick, I agree lead battery is good for doorstop. Attached the xls with more stuff including some SLA. The SLA price/kwh is beaten by nimh AA and in real life probably by the cheapest LiFePo4 too. And the longterm economy, weight and power is abysmal. Maybe I just did not find the good SLA deals.

I don't think RC stuff is too finick except if the choice of replacement bearings is poor - but this can probably usually be circumvented (external bearings/planetary transmission). I do not know anything about the durability of magnets in motors.

The 80-100-B that I was referring to has a noload current of 2A, it should be reasonably effy when cool. Most big rc motors I've seen are around 90%.
Given quality bearings, 6.5kw is a continuous rating if cool enough. Water cooling the stator may be the most compact and silent option for a boat, but depends a bit on the motor design. This may be where finick comes into play but you could always mount a fan to the shaft and derate the power if necessary. I've also considered heat pipes to aid air cooling or passive water cooling. 650w is not much when you have a delta of 50C or more.

The most efficient motor I know of is some (Australian?) solar car hub motor, cicero or something.. don't remember the name. This was an axial flux PMDC motor with no or very little stator iron. The stator pancake was in the hub and had magnets on each side of it, mounted in the wheel. effy > 97%. Tremendous torque due to diameter, but the weight was quite a bit more than an RC motor but still not heavy. With that eff you can probably do some serious overloading. Also, direct drive a big prop could be possibe.

 

Some good points, Rick. Seems we should consider Li battery price in Yuan to see how it goes. China has a history of low cost structure, but also of cutting corners and disregard to get there, so it's Caveats.

VRLA might be attractive for stationary applications like home power as the price drops to zero. Would be an interesting situation if it becomes price reversal where they pay you to take them away as recyclers shut down.

Vic

Porta

 

Sigurd
For the data file you should add some of the Kelly Controls motors and controllers.

Also the power density is possibly more important for boat and car motor applications than the energy density. I think any rating given at 20 hour rate is misleading for most propulsion applications. So you should provide a power density based on say 2 hour discharge rate. That is the sort of level that would be used in a fishing dinghy or yacht auxiliary. Needs to consider both current and voltage efficiency.

There is a good calculator for lithium versus SLA here:
http://www.valence.com/technology/lithium_phosphate_vs_lead_acid/#
I have attached the chart produced for a 40A discharge.

The small boat applications are typically considering 48V systems as this gives a nice ballance between voltage and current at the power level of most interest. So motors and controllers that can take this voltage will have a lot of interest.

Rick

 

I sent an email enquiry to Mr Jerry Yue seeking info and pricing on the Chinese LiFePO4 battery systems to suit my boat, Lets wait & see what transpires there

"Mr Jerry Yue,
Good Morning, I would like the following information by email...
Do you have any technical information on suitable batteries -
- A brochure in pdf format on any/all suitable LiFePo4 or other type of battery
- Charging regime and appropriate controllers / requirements?
- Cost for 220Ah 48V package for my boat,
- Special considerations for wiring up,
- Maintenance and lifespan/cycles
- Risk factors when compared to spiral wound AGM lead/acid system?
Presently, the charging system includes 'nominal' 1600W solar panels
22hp Kubota with twin 48V 'nominal' Delco configured in parallel to give 100A 'nominal'
Draw includes a full 240VAC galley (via 48V inverter 3800W / ~ / 10000Wpeak) and two
torqeedo electric outboards peak draw of 8800W @ 48VDC but usually between 2000 and
4000W when used and with genset operating in parallel with the PV solar panels & the
batteries if motoring or motor/sailing...
I look forward to your email..."

 

hi, with LI having an allowed continuous discharge of 2C-30C (60C is possible), and since I'm not interested in lead: energy density not power density is the interesting point for a boat. being able to drive for 1/2 hour is too little. In other words if you have enough energy you have also enough power.
The .05C (20h) rating you mention is for SLA, it is just another caveat to be aware of. In the case of LiFePo4, anything less than 1c means you probably can use close to rated capacity. But do check the datasheets to be sure.
I agree the .5c rated *watt hour* capacity would be a good comparison point for some but would require some research. As to the Valence calculator, when someone compares their product to anything "typical" I usually close my ears - interesting nevertheless. Feel free to mod the spreadsheet.

If you really want some power there is the A123 26mm. The energy price is also not too bad (ebay 4.5$/cell) and by all accounts I've seen they are robust, which brings about another point; the cycle life of 1000 is in this case based on 10c discharge. If you are more gentle, and keep them cool, I guess you may get several thousand cycles.

So in conclusion, yes the spreadsheet is on almost every point misleading... useable for quickly sorting out possible candidates. Power ratings too are to be taken with a grain of salt; the 5kw, 12-13kg mars motor is certainly going to stand more wattage than the 6.5 kw, 1.5kg turnigy, given that there is probably fatter copper so resistance loss will be less when overdriven.

Case in point about finick RC stuff; torqeedo is a modified RC motor as I mentioned above somewhere.

 

Rick, CDK, Sigurd, Porta and all who are willing to give me advise

Have you come accross any 8 -10Ah LiFePO4 batteries in a cylindrical type "D" shape. i.e. up to 35 mm diameter. I found one, but it has 38 mm and I don't want to start all over again.

Tell me whether I am flipping stupid and have wasted my money, or that I indeed have a concept and that I should carry on.

My concept is to have a casing wherein I can accomodate present batteries and future batteries. With a BMS, which with small modifications could be used for whatever technology. With sufficient power to drive 2 motors and which can be started with small and easy be build up to a larger energy capacity.

I have established that without too much contact problems I can pop standard off the shelve batteries into those pipes.

I have established that the weight of the batteries will secure contact, provide I make use of a Kontakt Chemie product. Either Kontakt 61 or Kontakt 390.

I don't want to use springs, as they make over a period of time bad contacts between the batteries. I use rubber force.

Should I ever get old and cannot lift heavy stuff anymore, that it is not a problem , should batteries have to be replaced.

If new technology developes I just swap the batteries

You converted me to LiFePO4 and I hope that the oilcompanies cannot pull a fast one us.

I have allways hired yachts all over the world and found that to be more practical for us. However, I feel that it is now the right time to build a boat for myself.

When I did my studies, I have allways been pointed out, preferable you do not connect batteries parallel. To my great pleasure, I read that even with Lithium you should be able to connect them parallel. I am totally confused.

If a diode is a waste of power, I have understanding for that. I could then use MOSFets and have a small power sources powering the gates with optocouplers and utilise the low resistance of the FET's and will no longer have high losses.

Anybody who has seen 2-20C discharging 8 - 10 Amphr type "D" LiFePO4 batteries?

Bert

 

Bert
I would be wary about any packaging that does not provide good cooling. I think one of the problems with imbalance in the lithium cells is temperature differential. Would not be a problem if the batteries are not working hard but if they are being charged and discharged around the 0.5C mark then temperature difference may be a concern.

There is a fellow, Bill Dube, who has made a fast electric bike using A123 cells who often discusses this problem.

Rick W

 

That applies to all electrochemical processes Rick. An increase in temperature raises the potential of a cell, causing an increase in V times A, so again higher temperature and so forth. Thermal runaway in plain English.
Discharging at or above 0.5C should occur only while accelerating, or the batteries need a heatsink. Ample capacity avoids the problem.

 

bertku, sorry, don't know about D. only a123 32mm are close but I don't know if you can get them - 26mm (C size) 2.3Ah seems to be the commonest.
That would give you ample space for the cooling pipe inside (copper water pipe).
The heat is dependent on internal resistance, high current cells would thus often make less of it. Rick is right about temp and balancing. Different temps on each cell can muck up the balancing electronics, if used, too. I too am curious to know about lifepo packs not using balancing.
Higher temp actually makes the capacity higher.
On the other hand, if you look at the A123 datasheet, and many others, you can extrapolate a doubled lifespan in case you go from 60celsius to 45celsius. Water pipes might not be the easiest way to do it though. Cycle effy of li is often 98 % or so, not much heat is produced with moderate currents. You can see on most of the commercial <5C packs and cells that not much effort has been efforted to make them get rid of heat.

yup, a diode has no less than 0.5v drop. with an fet you might decrease loss. 0.5v out of 50v is still just a 1% loss.

by the way sion power makes insane energy dense li sulphur.

 

Hi Rick, CDK Thanks for your help.
For that reason, to give cooling, I used those couplers, whereby air can flow between the pipes. Also I have the advantage that I can just cut pipes longer or shorter and place the pipes back. Only the bottom part is glued and firmly mounted.

I agree with CDK that I will have to be generous with extra LiFePO4 battery power not to push the batteries to their limits. It has always been one of my points to have plenty of reserve power.

But between the lines I can read that you are not too impressed with this "pipe" system, due to the extra weight it will add to a bank.

If I use those 38mm x +/- 200 mm 10Ah LiFePO4 at USA$ 17.00/pc, I will have to make a new bottom plate with 40 mm internal diameter. But it may have to be the route to go.

Bert

 

humm, your pipes are how large ID?


I've been wondering about this question for several years and would be thankful if anyone can help: Is there a waterproof (IP68) high current connexion available? 200A would do the trick.

 

At present I have 35 mm internal diameter pipe. But I discovered 38mm cylindrical 10Ah LifePO4 batteries. Thus I have to make a plan and either use 40 mm pipe without couplings, which means no more cooling, or I find Type D batteries with the same 10Ah energy content, or a battery which fit into the 35 mm pipe.

Do you have to connect while the 200 Ampere is flowing or you first connect the connector and then switch the power on. It will make a difference special with DC. Do you need to connect earth and a plus, both 200 Ampere?


Sorry I see what you mean. No, that is the length, +/- 200 mm, Sorry for that
Bert

 

DC 200Amp, but there will be no current while connecting. yup, ground and positive. 50v open cirquit

 

I assume you need it for your high powered batterypacks. The cable is that made of stranded wire of X strands by Y mm2 ???.

I assume that a manufacturer break it up in smaller connections mounted onto a copper plate and the stranded wire is then clamped or soldered onto the copper plate. The one row for earth and the other row for plus. The "stecker" is then pushed into a screwable waterproof, with "O" ring, casing. If they use 10 pins (5 per pole), it would only be 40 Ampere per connection.
Are there not 50 Ampere multipole waterproof connectors on the market which you could use?