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Author Topic: niMh VS Li-Po with Brushed Moters  (Read 5093 times)

irishcarguy

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niMh VS Li-Po with Brushed Moters
« on: November 02, 2011, 09:19:35 PM »

Im building a Robbe U47 my questions is batteries. I have a space issue in the WTC due to using an Engel 825 ml piston tank. I will be using a Robbe Rokraft 120P Controller, with the motors being brushed Graupner SPEED 400 7, 2 V and have them set up in a Ships N Things Double Fixed ratio: 3to1 frame. With that said it the NiMh vs. Li-Po. What I have read says must use NiMh 7.2V, but at a local R/C hobby shop they said I could use LiPo 7.4V. The Li-Po seams to win the size based on mAh ratio.
Understand that I must use a Li-Po battery charger, would like comments and opinions
Thanks,  John
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Mick B.

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Re: niMh VS Li-Po with Brushed Moters
« Reply #1 on: November 02, 2011, 09:32:32 PM »

You can use li pos. Please ensure you use a balence charger,and also charge in a ballistic bag.One last point please use lipo cut offs.To ensure that you do not overdischarge which will permanently damage the batterys. There is a not recommended way to recover over discharged batteries.John. 
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MikeA

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Re: U-47 NiMh vs Lo-Pl Batteries Brushed Moters
« Reply #2 on: November 02, 2011, 09:40:20 PM »

ive recently got into lipo i must admit there awesome. If you can use lipos then do in my oppinion, but you will need a balance charger to charge them, and a low voltage cut off or LVC. The lipo batteries must not drop under 3 volts otherwise they damage so some esc's have an LVC built into them which puts the boat is a slow recovery mode when the batteries are flat. You can also buy warning buzzers if the esc doesnt have one.

Saying all that would a lipo going into low voltage mode be a good idea for a sub  :o
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Patrick Henry

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Re: U-47 NiMh vs Lo-Pl Batteries Brushed Moters
« Reply #3 on: November 02, 2011, 09:59:54 PM »

John, re your question on lipos in subs...get in touch with John Robinson sub john on here, either by pm or by email...he is the AMS resident guru on all things to do with lipo batteries, what he doesn't know about them isn't worth knowing.

You could also pop over to the AMS forum and post a message there, John has his own little corner there, we keep him under lock and key!


Rich
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nige2307

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Re: niMh VS Li-Po with Brushed Moters
« Reply #4 on: November 02, 2011, 10:52:12 PM »

 
You can use li pos. Please ensure you use a balence charger,and also charge in a ballistic bag.One last point please use lipo cut offs.To ensure that you do not overdischarge which will permanently damage the batterys. There is a not recommended way to recover over discharged batteries.John. 

 
BUT it can be done.... NOT recommended, but with caution !
 I have recovered battery packs for my heli ( 32.00 each !)
BUT a ballistics bag or a decent sized pan (cheaper alternative) is a must.
 I have seen what happens when a battery decides to EXPLODE or go ballistic with rocket type propulsion,
and believe me, its scary ! 

p.s.  li-po's CANNOT be extinguished with water   DO NOT ATTEMPT !

nige
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Subculture

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Re: U-47 NiMh vs Lo-Pl Batteries Brushed Moters
« Reply #5 on: November 03, 2011, 07:50:20 AM »

Lipo gives the best energy density, but as has been pointed out, you must ensure you don't run them down too flat, which is easier to do in something like a submarine than an aeroplane.

You may want to take a look at Lithium Iron Phosphate batteries, also known as A123 batteries. These are slightly lower in energy density than Lipo, but still better than NiMH, and are far less sensitive to deep discharge.

Like Lipo, you will need a charger specially designed for charging these batteries.

Davy1

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Re: U-47 NiMh vs Lo-Pl Batteries Brushed Moters
« Reply #6 on: November 03, 2011, 08:15:28 AM »

I really would go for Lipos , if you wish to install them internally. (Lead acids are still pretty good in free flooding areas.)

I have been using Lipos for 4 years very happily.They give you much more flexibility when you are packing things into a WTC. As everyone says, use a balance charger + low voltage warning.

I'm not sure about the A123  lipo variant - they were very expensive when last I looked. Perhaps best to go with "mainstream" lipo technology.
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Subculture

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Re: U-47 NiMh vs Lo-Pl Batteries Brushed Moters
« Reply #7 on: November 03, 2011, 08:41:39 AM »

More expensive upfront. But cheaper than lipo long term.

sub john

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Re: niMh VS Li-Po with Brushed Moters
« Reply #8 on: November 04, 2011, 07:34:35 PM »

Reply to 2051476
   
First problem with using lipos in submarine is if cell splits and comes in contact with fresh water there will be a big bang, but if split cell comes into contact with salt water cell will be made harmless because if you wont to do away with a lipo cell you cut the jacket put it in a old bowl with salt water leave for 24hrs and then you can put it in the bin as it has been made harmless.

Second problem when using lipo cells no matter how good the pack is one cell will always go flat first,and every time the weakest cell is took below 2.75 volts depending how low it has been took below 2.75 volts it will loose so
much capacity  and will never get it back so that cell becomes weaker every time until the cell puffs up  mainly because it  has been under fast discharge.

Third problem because you won't to use it in a model submarine because the cell voltage drops off fast on a lipo cell you need to monitor each cell separate to make sure that the weakest cell will give you a warning and blow the tanks before cell voltage goes to low and damages the pack and you have not got enough power to get to the surface. Plus you need to be slowing down speed controller for main drive motors, to be safe you should be having a trip voltage at about 3.4volts to give your self time to get the sub to the bank side

I have plated about with lipos for many years now i was probably one of the first in the country to use them some of my packs i am pulling 3400watts at 42 volts that is alot of power plane will go vertical cloud base 

If you use lipo cell in submarine tags on end of cells i would cover in silicone rubber as if cells get wet alloy tags on end of cell will rot and drop off Hope info helps SUB JOHN
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Re: niMh VS Li-Po with Brushed Moters
« Reply #9 on: November 05, 2011, 11:31:37 AM »

A123 Life batteries tend to come packaged in a tough cylindrical case like NiMH or Nicads. For aeroplanes this means a weight penalty- not so good, but for subs, it just means a little less lead int eh keel. As they are far less sensitive to deep discharge, there is no real requirement for extra circuits to warn of low cell voltage etc.

The primary disadvantage of A123 cells is their upfront cost, although as the cycle life (2000 cycles) is far higher than Lipo or NiMH, over the course of time they work out cheaper than either battery technology. If you shop around you can find these batteries at lower prices, a lot of vendors on ebay are selling these batteries for electric bicycle conversions.

A secondary disadvantage is a smaller range of sizes/capacities when compared with Lipo. However in the case of the U47, this will not be a problem- the sizes available are just right for that boat.

More on this battery technology at this link- http://www.flyelectric.ukgateway.net/lithium-a123.htm

Davy1

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Re: niMh VS Li-Po with Brushed Moters
« Reply #10 on: November 06, 2011, 08:31:13 AM »

Thanks for sharing your experiences with A123 Life batteries, Andy. I would be grateful for more information.

When did you buy your first set? How much did they cost? How long have they lasted in your submarine? How many charge cycles have you had so far?
Which one of your sub/subs have you operated them in and for how long so far?

David
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Re: niMh VS Li-Po with Brushed Moters
« Reply #11 on: November 06, 2011, 12:08:41 PM »

Yet to try them in a sub, one person I know of who posts on here as 'Albion' is using them in one of his boats with good feedback. But I have been using A123/LiFE batteries for about 18 months or so now, albeit in model cars, (surface) boats and hedge trimmers of all things. These were all operating on brushed motors and controllers with no programmable voltage cut-off like this chaps U47. The power requirements of most model submarines are the same as surface craft.

Cycle wise, I don't keep a log, but they get well used, and unlike Lipo, which I've been using for about nine years, there has been no noticeable drop off in capacity after a few months of use. Some of the newer technology Lipos are reportedly better in terms of cycle life, but I haven't tried these, and they are more expensive.

I got my batteries initially by splitting a Dewalt power pack (the site I linked to in my previous post shows this) which was about a score off ebay.

However, it's now easy to purchase them in separate form. I did get some from this chap-

http://stores.ebay.co.uk/vpowerhk

But he seems to have recently stopped selling individual cells, only supplying packs now.

My favourite hobby store, HobbyKing supply them, but are a bit more expensive. There are also plenty of other vendors on ebay- the price drops quite a bit if you can purchase them in quantity i.e. thirty cells or more.

E.g. http://www.ebay.co.uk/sch/i.html?_from=R40&_trksid=p4634.m570.l1313&_nkw=LiFEpo4&_sacat=See-All-Categories

Patrick Henry

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Re: niMh VS Li-Po with Brushed Moters
« Reply #12 on: November 06, 2011, 02:50:38 PM »

What subs do you run, Andy?
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irishcarguy

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Re: niMh VS Li-Po with Brushed Moters
« Reply #13 on: November 06, 2011, 03:51:48 PM »

Andy, I'm building a Robbe U47 as stated above use Engel 825 tank with update motors from Ship's N Things. My thoughts were LiPo due to space limitations and trying to get the most mah
john :-))
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Mick B.

irishcarguy

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Re: niMh VS Li-Po with Brushed Moters
« Reply #14 on: November 06, 2011, 03:53:49 PM »

Thank to everyone who replied it gave me some food for thought.
John
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Mick B.

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Re: niMh VS Li-Po with Brushed Moters
« Reply #15 on: November 06, 2011, 05:16:07 PM »

What subs do you run, Andy?

A brief reply, as this is hijacking John's thread. Working at present- Seehund, Skipjack, Shark, Holland. I was hoping to trial the Skipjack at Brockwell, until Fusion cancelled on me. I rarely run the Seehund these days as it doesn't fit in the back of my mini very well. I was thinking of converting it to LiFE batteries as the old Pb batteries are getting a bit long in the tooth.

In the works- Aquabat, Yellow Submarine, Nautilus and Kittredge K-250 P-Submersible. The Aquabat is actually using a 3S 5A lipo pack, as it fitted well in the 200mm 80mm wtc I made for it. I'm planning to use LiFE batteries in the other three though.

bbdave

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Re: niMh VS Li-Po with Brushed Moters
« Reply #16 on: November 06, 2011, 09:00:56 PM »

I used to get 2 6v nimh packs in my U47 one to run motors one for the engel tank i had no space issues but i think Life batteries are the way to go more stable than lipo

dave
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Davy1

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Re: niMh VS Li-Po with Brushed Moters
« Reply #17 on: November 07, 2011, 10:30:41 AM »

So it seems that nobody here (including Andy) has actually used Life batteries in a model submarine.

So to answer John's original request, it may still be best to go with Lipo's , at the moment.

Some practical advice based on experience is always going to be more valuable than "thought experiments"  and stuff just copied off the net!

In the meantime, perhaps we can look forward to hearing more about Life batteries after Andy commissions his fleet, sometime in the future.
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Andy_k

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Re: niMh VS Li-Po with Brushed Moters
« Reply #18 on: November 07, 2011, 11:00:56 AM »

just when you thought it was save to get back in the water  :embarrassed:
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Right which one will I do next?;)

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Re: niMh VS Li-Po with Brushed Moters
« Reply #19 on: November 07, 2011, 11:33:51 AM »

There is another model submariner using LiFE batteries in his boats, who I forgot to mention. I think he's a bit of a novice- Norbert Bruggen.  ok2

Davy1

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Re: niMh VS Li-Po with Brushed Moters
« Reply #20 on: November 07, 2011, 02:35:15 PM »

Yes, and he does not write on this Forum.

C'mon Andy, get the dust off one of your models! Bung some LIFE batteries in it and show us all a the video of it performing.

Less pontification and more practical advice, in my opinion.

You would do us all a favour.

Thanks in advance.
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Patrick Henry

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Re: niMh VS Li-Po with Brushed Moters
« Reply #21 on: November 07, 2011, 05:48:30 PM »

Now here's an interesting little thing worth trying...I was discussing this with Nigel (AMS Chairman) and between us we came up with this idea. May well be worth a try..

Ok, so we know that if Lipo batteries get wet, there will be a big bang in your wtc, which by it's very nature won't do your boat much good. And if your boat has been down a while, there's every chance that when it's rescued there will be water in the wtc...maybe it's not found it's way to the battery pack as yet, but as soon as it's tilted, the water may run to where the battery pack is...resulting in aforesaid big bang which may well cause damage to the rescuer as well as your boat.

Now, we also know that dropping a Lipo battery pack into salt water will kill the battery completely and render it harmless.

Ok, so how about adding salt to your wtc? No, I don't mean getting the salt cellar out of the kitchen and sprinkling everything with salt, but adding salt into water soluble bags and placing a couple at either end of the wtc...see what I mean? You can buy water soluble bags in any fishing tackle shop, or you can empty out a couple of dissolving tablets and fill them with salt.

Now, if your boat develops a major leak and water enters the wtc, it will start off a reaction which will melt your water soluble container, be it a bag or a tablet case, and the salt will mix with the water, which in theory will kill the battery pack before the big bang happens.

Please note that this theoretical and as yet hasn't been tested, but it may well be worth a try...it may well save your boat from destruction at the cost of a battery pack. Sounds like a good deal to me.


I would welcome your comments or your criticisms, gentlemen...


Rich
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Albion

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Re: niMh VS Li-Po with Brushed Moters
« Reply #22 on: November 08, 2011, 10:30:14 AM »

Use A123 LiFe instead and then dont worry about it :)

I have Life's




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Davy1

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Re: niMh VS Li-Po with Brushed Moters
« Reply #23 on: November 08, 2011, 10:45:55 AM »

Excellent.

Please share your experiences with us.

David
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Albion

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Re: niMh VS Li-Po with Brushed Moters
« Reply #24 on: November 08, 2011, 10:47:33 AM »

The first post shows 13.2V worth of 26650. I originally had 2x6V gell cells upfront. Changing to the lighter A123 i am able to double my Ah rating, plus fit a ballast shfiting device to vary trim. I must take a photo showing the final fitment of the batteries as its slightly neater.

in this photo ive got 6.6V of 18650. Though this one isnt running yet. Its a Revell Type VII, orignally built using the big dave WTC, however it had issues. So i am dropping in the D&E gas/snort type WTC. as you can see the batteries are a good fit.

Its just a battery. Seems like Lipo take too much care for my liking so i went for these.





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