Powering Micro Sub

[Submariner]

Looks like we lost Jeremy, I know he's busy.

fechter: I don't intend to use the $22 controllers from china but I was interested in Jeremy's comment on them

and to know more about them. I'm learning.

dragonfire: I don't intend (nor am I able) to spend that kind of money, or have that kind of complexity. K.I.S.S

nutsandvolts: Don't over credit the personal sub guys. They don't do a lot of "cruising around". They're mostly

into going down for a while and coming back up.

john in CR: I've researched nozzles thoroughly. They only work at high thrust and low speed. I have neither.

In my situation they would produce more drag than benefit and have a negative effect. What more info would

they like on the motors? I tried posting on the Technical forum as you suggested, it's not possible, it is

reference only. FYI this is not the ebike forum it's the electric vehicles discussion forum. I thought it the

most appropriate place to post after reviewing the options as this is a vehicle as are airplanes and space craft.

I have plan a, b, c, d, e, f, g, h, i, j, k, l, m, n, o, p, and q at this point, but thanks for your concern.

The potentiometers are intended to direct the controller. None of this should be brushed, it all needs to be

ignition protected, no sparks. Please, what should I be using? Do the research on low thrust, contra-rotating

marine propeller drives and let me know if it still feels wrong. It's not one shaft, it's two (see thread).

Malcolm: In reviewing your calculations I believe you were assuming 12 volt batteries, mine are 6 volt.

Although Seadoo or troling motors may seem atractive they have lots of shortcomings for my application.

vanilla ice: I think I missunderstood your question, you tell me. Are these batteries appropriate?

 

[dragonfire]

since you brought up the "no spark" point: will the batteries be stored in an airtight/ gastight compartment in which this rule ( no spark) won´t apply but the problems of gassing out batteries have to be somewhat taken into consideration ? as for the 22 $ controllers, i am plenty sure they will not serve this safety feature by a certainity you should require of it if i am guessing right for the (obvious) reasons when using pressurized oxigen in the capsule.

 

[Submariner]

dragonfire,

No, the no spark rule must apply throughout the vessel.

There will be no pressurised oxygen on board, other than the ~20% found in air.

Tom

 

[Malcolm]

Malcolm: In reviewing your calculations I believe you were assuming 12 volt batteries, mine are 6 volt.

My mistake, my estimates were based on 12V batteries not 6V, so for a 6 kWh pack based on your existing batteries that would be 8 banks of 10 batteries wired in parallel.

The 3 kWh requirement I gave was a guesstimate - so I have a few questions myself, just to try and get a better idea of the performance and capacity requirements:
Where does the 10 kW peak requirement come from? I imagine you've already done your own power calculations, but just to double-check.

What would you consider a comfortable lower cruise speed and have you calculated the power required to maintain this speed?

Why does your friend recommend 36V? Is that to suit his own motors, or is there some other reason? Producing 10 kW from a 36V system naturally requires more current than from a 48V system. This in turn means more motor heating (proportional to current squared). Heat build up over the course of an hour could become uncomfortable in a confined sub.

I'd echo what others have said and suggest going with a known reliable combination of motors and controller, running at the highest voltage you feel safe with.

Why the need for spark-free equipment? Is this just a general safety requirement or a consideration for the lead acid batteries?
(dragonfire: divers don't use pure oxygen as it becomes toxic even at shallow depths, though they do sometimes use slightly increased oxygen levels for relatively shallow dives). How spark-free does it need to be? Does this extend to all switches?

Malcolm

 

[spinningmagnets]

I must agree. Do not bring pressurized oxygen any where near the vessel. Should a salt-water leak occur in the separate and sealed battery compartment, a relief valve should vent overboard to allow the poisonous/flammable gas to leave.

It might be wise to add a pressurised air-bottle and a Lithium-Hydroxide filter to absorb CO2, they dont take up much room.

 

[Submariner]

The no spark rule seems a prudent safety measure to me. I don't know how spark free it needs to be but 100%

comes to mind. Does this create a big hurdle? I have electrical knowledge but limited practical experience.

This machine is incredibly simple and relys little on electronics accept for the drive train.

I agree with the proven equipment concept 100% but what is desirable with these motors is at 36 volts they turn

1000 RPM. The builder (who has a formal electronics education and carreer) feels 36 volts a safe limit for a

submerged, salt water, confined space. They are also hollow in the centre allowing a solid drive shaft to run in a

counter-rotating hollow shaft to each prop. No gearing. It's a very attractive scenerio. I am a very cautious man,

father of a three year old and would certainly do a LOT of testing and proving before going this route, but I

have to investigate it. I will be in a 1/2 inch plywood box within the sub. The exhaust cabin

air that vents on each partial or total ascent, will vent past the batteries and motors. To vent the batteries

seperately is not physically possible. The best I can do is keep them down stream. Also, I will be breathing from

a SCUBA regulator, with a mask, for safety (CO2, H2, flooding, etc.). My seawater temperature is 9C (47F) outside

of a 1/2" fiberglass hull. Also, the prop hubs will likely be aluminum or steel and there could be additional hull

cooling if necessary. Eight banks of ten batteries is beyond my present design limit (space and weight). As you

can appreciate, change one thing in a submarine (or submersible) and you change everything. Kind of like a

jigsaw puzzle. Yes, my power reqirements have come from calculation which I am very confident in.

Power has a cubic relationship with velocity in a sub. So, 4 - 5 knots would be a low end speed expectation

and would use perhaps 1000 watts. I think your 3kw was a very reasonable guess, 2kw/hr may even be closer.

Needless to say, I will be very conservative in my initial sea trials which will likely last a long time

(i.e. many trials). These motors are 4 kw so I loose a knot, no big deal. 14 knots vs 15.

dragonfire (on a PM) feels these SLA's are too thin plated to withstand the loading I'm proposing.

It sounds like if I want to use these batteries, I may have to tone down the power demand and loose

some top end (max speed) or at least some duration at full throttle...

Thanks for your interest,

Tom

 

[dragonfire]

the pm you reffered to wasn´t sent by my, but the author is right nimh won´t serve the power output yu want on a small physical footprint. nimh may be an option, but lifepo4 seems the best choice if it comes to safety with high storage density and good capabilities to be overcharged and discharged.

but there are good sla chemistries out there, too, the 12-12´packs accept twice the peak output of the 12-7/9 cells.
Panasonic LC-RA1215P ( 12v 15ah, ) and it´s outstanding characteristics ( burst discharge per cell 195 amps, 6-9 yrs lifespan, certified for medical devices...) seem to be suitable. 3s4p of them in parralel should suffit. Panasonic seemingly also has nice stuff in the smaller 12v-7ah/9ah seize:
The Panasonic UP-RW 1245P1 . Allthough no mentioning about lowest advised voltage or maximum charging currents, a certified discharge rate of 268 watts/ 10 minutes per batterie sounds promising, alongside with 6 yrs lifespan and the fact that these are permanently charged at 15 volts in the epsu-systems they are designed for. these have a internal resistance below 10 ohm i believe. maybe a 2s5p setup of the 12-15 ´s and a booster pack hooked up in series to each bank consisting of one of the 1245P1 ´s to get your 36 volts and have both high discharge capacity and stable basic power ?

edit for safety:

a plywood box is not airtight. seal that up and only open this box when charging the batteries to allow them gassing out. if you ground your voltage to the water make sure that the cabin is opened and gassed out, same with the battery box, before lifting it of the water.
since you use a glass-fibre hull you can carry a cutter with you to allow for an escape exit if you get caught in a net or cables or whatever else may stock you when doing dives in canyons or whatever (so no explosives needed to split a steel shell).
if you are not too deep this should work, even with the rapidly altering compression states- but some emergency flooding valves to ramp such an emergency escape smoother can´t hurt.

also , check into oxigen generators like used in airplanes, they have to be replaced periodically but are still good. these heat up pretyy well when used, but they are small and can get you some emergency air pressureinto the cabin in case of a leak.

 

[Submariner]

Pardon me dragonfire, my mistake, it was drunkskunk's PM, I apologize.

I'm really just looking to power the sub not redesign it.

I'm on this forum for electrical and electronic advise as this is not my forte. I realise this may overlap into

overall design, but I can sort that out. You're going to have to dumb down the terminology/jargon in your

posts if I am to get much from them. I have had some electronics education so I know the basics but am

by no means up to date nor conversant as the majority of participants here.

I do appreciate your efforts, it's a shame to see them go to waste.

Thanks, Tom

 

[dragonfire]

not a problem if you are unsure about how to set the batteries up:

all batteries will spark when grounding is there and they are hooked up to the device. this may also occure if grounding is interrupted due some event, so make sure the batteries are sealed if your air coudl react with it.

the batteries themselves, you´ll want a 24 volts controller than can take 36 volts safely and go up to 45 volts cause that´s where the following setup will be at if fully charged:

2 12v15 ah batteries in series ( ="S"), 4 of them in parralel (="P"), this adds up the voltage of the batteries if in series and the ampere-hours (durability) in parralel.
then you´ll have a 24 volt setup.

you mentioned you would like to have 36 volts allthough the designer pointed towards 24 volts, so you will use this extra-power only to "boost" in streamings or whyever.

you could also have a look int 6 volt cells with equal ampere´s this will double the boost time.

this leds to the booster pack setup, connected in series (so it will increase the voltage) of each of your four parralel 24 packs. this pack ( connected by a switchable ( due current demand of throttle) schottky diode) will have lesser ampere-hours as it´s only one batterie compared to the 2x12 volt packs for regular operation, but they deliver their volts and also ampere´s faster than the 24 volt setups chemistry and thereby prolonguing the operating time of this pack cause they deliver faster on all load conditions ( cause of this you will want the switching diode and it should be a schotky cause it´s simple and does not allow reverse charge of the 24 volts pack to the emptied booster pack) and thereby keep the distressment of the main pack thus reducing peukert effect and general draw so you will prolongue your operating time per weight of batteries and still have the advantages of a 36 volt setup when needed without the paermanet load on batteries required for regular 36 volt operation.

as for controller, i´d recommend to get a 25-5000 ohm controller ( "5k ohm" ) and throttle cause you can add on nice little e-bike and scooter gimmicks like cruise control and also this will draw the batteries by modulation on current needed and not voltage available, alowing for a better control and also saving on battery lifespan. and you could use that to allow switching to the booster pack not in manual or by a releais/ diode but a mosfet or thyresistor setup, but this is non-needed complication for the first setup atrempt if improvements on details are scheduled as ongoing progress in the built touched water several times.

i´d also recommend a balancing wire in between both banks.

 

[Malcolm]

Hi Tom
Thanks for the info. Yes I can see there are big advantages in using the hollow shaft motors your friend is building. 36V also makes sense for low prop speed. Motor cooling may be an issue, but if you keep the prop shafts as short as possible you should get some useful seawater cooling. I'd recommend testing the new motors with an industrial quality controller such as the Sevcon that Fechter mentioned, and which I linked to earlier. You'll need one for each motor if it works out OK.

Assuming a 36V system and a useful pack capacity of 3 kWh (which again means a rated capacity of 6 kWh for lead acid):

6 kWh divided by 36V is roughly 168 Ah, so you need a 36V pack with a capacity of 168 Ah.

To get sufficient capacity with your existing 12 Ah batteries that would mean six banks of 14 batteries, which would mean a lot of connections and a lot of possible failure points. I'd suggest looking instead for some good quality 6V or 12V batteries of sufficient capacity that you only need to use three or six batteries in total. It may take some looking around to find batteries of the correct form factor to fit in your available space, but I have seen large capacity deep-cycle batteries in a long, slim case – just can't find the link right now.

For switching and isolating the battery pack from the controllers, I'd recommend a pair (for redundancy) of enclosed heavy-duty contactors, such as the EV200 (ebay item number 200363534803).

What else do you need to know?

 

[dragonfire]

this much energy would suffit to drive 1 hours at speed as it seems, and industrial controllers ( forlifts ?) seem a good idea, too. you wouldn´t wan tto rely on chniese untested and unmatched controlelrs for that, due the lots of handcrofting there may be differences in internal resistance or even parts/ wires even if both are of the same batch.

as fro deep-cycle sla s, if they don´t have to be slim there are fairly big car batteries with 12v and up to 180 amps each easily available, looks like a non-stacked 10 cell design so these shuld be rockstable even in after several cycles and without balancing ( given the idea the recharge will take place with one charger and each cell after the other one)

 

[Submariner]

Thanks Malcolm, that's great. Unfortunately, I am constrained by dimensions with the batteries.

My space is small and tear-dropped shaped with the widest point being 16 -20" (not yet finalized).

A huge advantage of the batteries I have is their size, 2 X 4 X 6 inches. I am able to fit them in above

and below my prone position. I'm thinking I need to alter my speed objectives. More steady state

1000 watt cruising and less (if any) full throttle time. Maybe when these batteries are toast

I can invest in some high power density "wonder batteries" eluded to earlier in the thread. The R300

of Cliff's (web-site posted previously) uses deep-cycle, 6 volt, golf cart batteries. He's got the space

but not the performance. Ha, neither do I now that reality has set in.

Maybe I need to go back to the drawing board and look at a larger diameter vessel that has room for

those big batts. The second largest contributing variable in submarine speed is diameter, how big a whole

you need to open up through the sea. The first of course is velocity. These motors are about ten inches in

diameter so the shafts end up being about two feet long. Although, I could flood the shaft area.

How do you feel about the 48 vs 36 volt safety issue?

My contingency plan, should I flood, is to beach, which should be feasible as I'll be operating in shallow water

near the beach, so long as I still have propulsion. Now this would be at full throttle with "sealed" electronics.

If flooding is too rapid then it's evacuate with the scuba tank and lose the sub to the shallow ocean floor for

subsequent recovery. Motor flooding will be delayed but inevitable. The battery terminals would likely be the

first electrical component to see salt water.

The long slim SLA I know are 2.2 volt, single cell units about 150 pounds each. We used 7 of them in series for

solar powered, mountain top earthquake sensors here.

Thanks for all the info Malcolm, I really appreciate it.

Tom

 

[dragonfire]

solar charged seismic sensors have a far lower charge and discharge current than your project, having 6 x 6 volts in series and many in parralel will require balancing both on charge and discharge, since this endevour will require many connect diodes you will have to have a active balancing system cause the exact resistance in between these diodes will vary a little. you´ll run into the more complications the more cells/ batteries you use.

as about the design, will the batteries be positioned at the bootom of the submarine to keep it balanced that way or is there a way the battery box can be placed as a seperated section ( full or half-moon diameter of the sub) in between rear engine and passenger zone ? this way the battery bay could bring some additional strengt to the scelleton and also be tightenen (airtight9 more easily, allthough most of the sparking will be done at the controlelrs if anything is mounted right i believe (?).

As for sealing this all up, there is another thread in the forum about a guy who wants to make his hubmotor (in a wheel9 watertight. what kind of bearing (-s) will you use on your driveshaft, what lubes ( since not all have access to fat of whales or other exotic crap) help to keep the driveshaft rotating in a solid bearing and stillseal the water ?

 

[Malcolm]

Yeah I know, it's a bugger having to compromise on a design you've tweaked to near perfection If you could just distribute your own body mass in the spaces that are left over after fitting batteries, motors and air cylinders it would be much easier ...

OK, just for comparison, if you were to go straight to lithium batteries, you could roughly cut the volume in half and cut the weight to one third.

To give 3 kWh of useful energy you would need a 36V 100 Ah pack (lithium can deliver much more of its rated capacity than lead).

This could be made up of twelve 3V cells http://www.evcomponents.com/ProductDetails.asp?ProductCode=TS%2DLFP100AHA, each measuring 145×220×68 mm and weighing a total of 43 kg.

The drawback is that you would need an electronic battery management system – a circuit board(s) with connections to each cell that makes sure individual cell voltages do not go too high or too low. These can be bought off the shelf, but obviously add to the cost and would require waterproofing.

As far as safety is concerned, I don't think there's a big difference between 36V and 48V, but I don't have any experience in underwater applications so if anyone thinks otherwise please jump in. A brushless motor should run underwater without problem, although it naturally won't do the bearings any good. If you keep the electrical system simple I don't see any reason why it shouldn't carry on running when flooded. You will lose some power through electrolysis at the battery terminals, but I wouldn't expect it to be excessive. (I remember producing some very noxious fumes when I played about electrolysing brine as a kid, but if you're wearing scuba gear that's not a problem.)

 

[Submariner]

Hi dragonfire,

I have no intension of using those 2 volt batteries, I was just sharing what I knew (not much) with Malcolm.

They are what I'm familar with, what I've worked with, what I know and have wired, metered, carried, slung by

helicopter, etc. So, the batteries I have are 3 cells each, as you may already know, and there sure would be a

lot of cells once all wired up. I had no intension of using diodes at all.

I've been trying, again, to get some drawings posted to give a better idea of what I'm doing, but this old Mac

(10 years) just doesn't want to cooperate with this forum. So, I'll have to tell you instead. No, the batteries

are not on the "bottom". This is a very unconvensional sub, it is asymmetrically balanced. What I'm after is

jet fighter performance and handling, or at least as close as I can get. I have an extensive background in scuba

(instructor, construction, rescue, even logging, etc.) and am completely bored with it. I have 83 hours on a

private pilots license from when I was a kid and thought I wanted to be a helicopter pilot. I have both

motorcycle and car racing experience. I have a Mechanical Engineering Technology diploma from 1983.

Plus a wack of other crazy experience. The batteries were to be placed above and below my prone position

creating zero intrinsic stability, no righting moment, zero inherent stability. This makes for crisp roll response,

driver control and manoeuvrability. Again, I tell you all this in order for you to better understand my intensions

not so you can redesign or "improve" on it. I've been working on this concept / design for over a year and have

done a lot of research and development. It turns out I should have done a little more on the powering issue

first. I thought I would be okay with what I had.

Because this is a delayed ambient pressure design, it's very difficult and complicated to isolate the batteries

from the cabin. Complicated is not good in my design, it relies heavily on simplicity. (My wife laughs at this one,

she says, "The words simple and submarine do not belong in the same sentence". She makes a good point but

I beg to differ.) I can however direct air flow, so I'm keeping the batteries downstream of the controller and

my mouth. Although I am breathing from a scuba regulator, in the event of an air supply failure, I will have to

breathe the cabin air for a while. There is no conning tower, the only way in and out of this thing is on the

trailer, accept in emergency, but that means losing the sub to the ocean floor.

Thanks for your input though dragonfire, I do appreciate it.

Tom

 

[Submariner]

Hi Malcolm,

I didn't see your last post until after I wrote mine. With a three year old around it can take a while to compose.

It's not so much that I've tweaked the design it's just that so many things depend on another in a submarine, it's

really difficult to just change something without affecting ten other things. And it's really hard to simplify

systems as well, but thanks for your empathy. It would really help if I could post a couple of my drawings.

I tried using the "post an image" button but I just get: {IMG/IMG}, I tried clicking and dragging from my

desktop... I love technology but I hate computers, sad but true.

Thanks for the lithium info. The weight loss for me is a detractor as I really do need the weight. Everything can

come out of the sub for charging so it may not be as complicated as you propose...? Ah, but they also have to be

monitored for low charge, so on board, I get it. Well, with so few batteries (compared to what I'm proposing now)

that's not a big deal. I think I need to see about dropping the high power time and making what I have work.

If it's all a go then I'll look at new batteries. I'm also going to kick around the idea of more appropriate SLA.

If you can find that web-site for the long, slender ones you mentioned, I'd be interested. Otherwise, it seems

like golf-cart batts may be the way to go, but they're so dimensionally huge. I'll have to look into alternatives.

I suspect that my current design will stick with lithiums down the road.

As part of my due diligence, may I ask what your background is so I may weight your advice?

No offence but it does seem prudent to ask. Feel free to personal message me on this if you prefer.

Thanks again, Tom

 

[Malcolm]

If you let us know what type of file you're trying to post, maybe someone who is more computer savvy than me can help you post it (I'm a mac user myself).

Yes, you can separate the battery management system from the batteries, but as a minimum you would still want a low-voltage warning for each cell. There are a few BMS boards available now that are designed to bolt directly to Thundersky type cell terminals – one per cell. These could be given a conformal coating to make them water resistant at least - I'm not sure if such a coating is actually waterproof?

I'll see if I can dig up a link to the batteries I mentioned.

No offence at all. My background is mainly as tinkerer. I've been soaking up everything I can about electric vehicles for the last three or four years and converted a motorbike which I'm currently (slowly) modifying for lithium. I have a bachelor's in metallurgy and a master's in welding & offshore technology (rigs), but it's about 20 years since I actually worked in that area. Now a technical translator. I qualified as a recreational diver a few years ago and have a couple of hundred dives.

If anyone here thinks I'm giving unsafe or inappropriate advice I hope they'll put me straight, and if anyone else has advice to offer please do. It seems unusually quiet around here right now. Everyone out making hay?

Edit:
It may be necessary to waterproof the hall sensors in the motors (they control phase switching) to prevent them from shorting in case of flooding. There's a related thread here: http://endless-sphere.com/forums/viewtopic.php?f=10&t=11758

Malcolm

 

[dragonfire]

Hi Submariner,

there was no intention from my side to play a smartass-role about your design, it was the way you jumped into the idea and underestimated the electrical part of it that made me question your concept on a more rudimental level than obviously suiting your experience on topic ( of submarines).

the reason that brought me into recommending oldstyle "big block" ( few big cells per battere instead of several, keeping in mind that sla´s do not interact well will salt water) is that this concept was used in military submarines over decades cause it was not requiring complicated/ suphisticated methods of balancing, you could recharge these cells with a car batterie charger one after another and they would still remain ad a similar level over plenty cycles. Another reason to wait with lipo´s ( beside complications in battery management) would be that there will be mayor effects on pricing and availability by the stimulus packages of several nations hitting in round about now. the price will drop significantly in after the first stimulus waves are over ( mid-end 2010) and the choice of batterie types and chemistries, some if not most of them prepared for safe use in vehicle applications ( also controllers and chargers), will also broaden up quite a bit.

since you will obviously steer the vehicle in manual and permanent regard of the both propellers to run in a fashion that you are not a seadrill but a sea-jet you will want those industrial controllers and stable battery chemistry for stable output on both propellers. will you run each engine on separate circuits ro of the same power source, if you mind me asking ? cause if running them of the same source only one stucked propeller may block both by taking all the current until the controlelr shuts down, just a non-finished stomach concern atm but you may want to follow up on this.

since you mentioned you will only get in and out the submarine while on trailer you should also make sure the trailer can take the grounding voltage of the battery ( no rubber isolation in between trailer and sub) and the fibre-glass body has some sort of grounding cable that will be in the water or grounded to the trailer all the time to avoid sparks,
The drop-design with such a balance, only a vertical rudder and angling into corners by simply adjusting the counter-rotation of one( both propellers sounds beautifull, who needs loopings if he can do barrel rolls and angled turn like on motorbikes but minute-long and without real risks all day long, all that without extensive power consumptioning. Nice.

 

[KAE]

You may want to consider LiFePO4 cells, as they are smaller and lightweight in comparison to SLA's. They are also non-toxic, and safe. They are completely sealed, however they must be kept in a waterproof environement for safety reasons. I primarily use them for electric motorcycles, however, I am meeting this week with a designer for electric submarines and ROV's for ocean research. He has designed lithium-ion battery packs for underwater submarines before and is very knowledgeable on the subject I will ask him for some more information for you. Cheers, best of luck with your project!

 

[dragonfire]

lifepo4 looks great at first sight an per cell, but on an application like his the complexity in balancing and potential failures seems hefty in the dimensions of a diy-project. since the sub will be to small to reasonable accomodate big batteries they may be the only remaining answer, back on sla the panasonics and the Oasis design looks promising. if the vessel gets a tad bigger and pricing wasn´t a concern ( plus there is a solar or wind-power installment at your house to keep the batteries toppe dof) you may also want to look into Zebra-batteries.

the next few moths will bring interresting market entries in the field of Zn-Air- batts with non-crrosive lithium anodes and more advanced layer lamination technology ( stable in more tmeperature and surrounding conditions) Li-Seawater cells, these will be close as good as the military silver-zinc chemistry ( up to 11 00 wh / kg) but not use up as fast, these would be the perfect 2011 batteries in your application- keep in mind that the development and market-entries in the fields of batteries will outsurpas almost any other industry in the next few moths and years, so it may be good to take this insto consideration on both the builts dimesnions and also the controllers and other components setup and capabilies.

 

[Submariner]

Fantastic, thanks gent's.

Funny about these hall sensors, my friend doesn't know of them. I suspect it's because he's using optical

sensors. I'll run one of his motors in water and then in sea water if I get that far with them.

In fact, I'll probably run most of the components in salt water and take some measurements if it looks,

down the road, like I'm going to use his motors. He's trying to develop what he calls the Electric Hubcap for

cars as a hybrid assist. He's a smart guy and very eccentric (kind of like me...).

It's funny, I just can't quite convince this crowd that light weight batteries are not good for my application.

I realize, it's a very unusual circumstance. However, if the batteries were small enough, I could fill more space

with them and just ballast the difference. The craft is neutrally buoyant ( well, actually -2.5 pounds or 1kg

on launch and +2.5 pounds after one hour. That's the weight of 70 cubic feet of air I might suck up).

Redundancy in the drive train is a huge safety feature. Both props, motors, controllers, controller

potentiometers, battery banks and wiring must be completey seperate in order to achieve this.

The only common item will be the knob on the dual (or double?) potentiometer for synchronous motor

control. Roll, yaw and pitch control will all come from control surfaces. Submarine props can be easily

cavitated (lose their "grip" with the water and "spin-out") so fine motor control is a necessity. Rolling by

differential torque is not very responsive or effective.

If I ground the electrical system to the sea water do I still need to ground to the trailer? The trailer will

be in the water when I board it...

What I'm trying to post is a JPG...

KAE: Thanks for asking around, be sure he understands this torpedo is manned! I know some of these guys.

Who are you meeting with?

dragonfire: I didn't think you were playing "smart-ass" I just don't want you to underestimate the

complexity in my attempted and apparent simplicity.

Malcolm: As always, thanks for the info. BMS ??

Cheers, Tom

 

[KAE]

I'm meeting with Daniel Gomez-Ibanez from the Woods Hole Oceanographic Institution, I'll be sure to bring up your application and see what he thinks as it is very interesting! He is a battery pack designer for underwater vehicles so he should have some good pointers for you possibly. You can read an article about the latest sub project here:

http://www.whoi.edu/oceanus/viewArticle.do?id=57648

 

[Malcolm]

Sorry, BMS = Battery Management System.

A couple of links to lead acid batteries:
http://www.enersysreservepower.com/safe_vx.asp
http://www.enersysstationary.com/documents/US-VX-RS-003_0107.pdf
These batteries are used in back-up power systems and tend to be routinely replaced after 3 or 4 years of very easy life. In the UK similar batteries regularly come up on ebay for around $60-70. I know someone locally who has been using a second-hand set in a 50 mph milk delivery truck for several years, and he swears by them.

Thinking about hollow shaft motors, you may be interested in this thread: http://endless-sphere.com/forums/viewtopic.php?f=10&t=7718&start=15
It's very long, but you could always ask Mark if he thinks his motors are suitable.

 

[Drunkskunk]

It's funny, I just can't quite convince this crowd that light weight batteries are not good for my application.

I realize, it's a very unusual circumstance. However, if the batteries were small enough, I could fill more space

with them and just ballast the difference.
Cheers, Tom

I think you missunderstand. Its not that we're recomending the other batteries bassed on weight. its Size. you have a limited volume you can fill, and other forms of battery are lighter because they are more energy dense. I.E. smaller. you can be more creative with the battery pack design and fit it to the space you have. The weight at the end may be the same, with larger capacity.

BMS (battery management Systems) sounds complex, but in many cases, they are only needed during battery charging. They are designed to shut down the battery if a fault is detected. In most cases, in a sub or airplane, you might rather let the fault kill the battery instead of letting the BMS save the battery and kill you. I don't run a BMS on my bike, but I have a type of BMS built into my battery charger. The only protection on my bike is a volt meter, and knowledge that a specific voltage means empty, and below that means empty for ever.

 

[dragonfire]

in a submarine any batterie failure in operation ( using one of the more energy-dense and instable materials and composites) can lead to sparks, fire, smoke and high heat not suitable for a glass-fibre unibody hull or when being submerged in one. so a good bms for every cell in the pack and setup will be needed on anything but sla. this can well be handled seperate from charging balancing but the easiest way is having a connector ´( variety of types and concepts to choose) that shuts of at low and high voltage, and this per cell, if using lipo or in a submarine.