LiFePO4 could this be the new wave in boat batts

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Peter Allen
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LiFePO4 could this be the new wave in boat batts

Post by Peter Allen » 09 Sep 2009, 16:47

Found this on the web this morning,with my limited knowledge on anything that shocks burns or explodes ,maybe the experts can tune in.What i've read is they seem to be similar in current and weight than LiPo,but not prone to explode(rated safe as MiMh and Nicad).Also very cheap www.batteryspace.com The 103g 6.4V 1300mah pack USD$11.95 and the charger$23.50.One thing that i cant understand is when moving up to 150g 1650 mah, the pack is made of 4 batteries rather than two as in the 1300mah pack and obviously weigh more.The Batteries are claimed to be 3.2V per cell.HummPeter

Nigel
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Post by Nigel » 09 Sep 2009, 22:28

Peter, I have been using these batteries since the end of 2008 and am very pleased with them.

A two cell pack has 6,6V at 1.100 mAh and ways about 90g. You can charge these batteries with 3C so can recarge a pack in 20 Min. The have very low internal resistance and can easily handle loads up to 50A. They can be charged with dedicated chargers or the LiPo program is fine as well. They have a low discharge rate and are mechanically a lot more robust than LiPos.

All in all for me they are the best cells since NiCad. NiMh I found very sensitive regarding storage and maintaing the nominal capacity, LiPos are to hazardous for me. LiFe do everything we need and are easy to handle.
Nigel Winkley
GER 87

Peter Allen
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Post by Peter Allen » 10 Sep 2009, 02:13

I am going to bite the bullet and give these things a try.Nigel if yourself or anyone else in the know could give me some advise,i am completely ignorant of all the jargon connected to this tecnology.I am looking at two batteries on www.batteryspace.com the first is LiFePO4 18650 Product ID#3789 6.4V 1350mah(flat,8.64 Wh,4A rate)max discharge rate 4A and the other LiFePO4 18650 product id #3921 6.4V 1200mah(flat7.2Wh,14A)Max discharge rate 14A.What i'm looking at here is not the1200-1350 mah but the discharge rate of 14A on the 1200mah batt opposed to 4A on the 1350 batt.What's it all mean,i have no idea what that stuff in brackets means,which of these two batts has the more capacity?Or is it just that simple that 1350 mah is it.Same charger recomended for both.Thanks Peter :roll:

Hiljoball
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Post by Hiljoball » 10 Sep 2009, 04:06

If you are running an RMG winch, then consider the 9.6v 1200ma pack. (especially if you have some corrector weights that you could remove to counter the slight extra weight over the 6v pack).

The RMG should really fly on 9.6v LiFePO batteries.

http://www.batteryspace.com/lifepo41865 ... witch.aspx
John Ball
CRYA #895
IOM CAN 307 V8
In my private capacity

Peter Allen
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Post by Peter Allen » 10 Sep 2009, 04:49

The RMG winch is rated at 9V max.

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Post by Nigel » 10 Sep 2009, 11:49

Peter,

go for the 1.350mAh. It gives you a little more capacity. I just checked mine and they are actually exactly these cells.

The max. rate of 4A ver. 14A just gives you the maximum load you can apply to the batterie. The max. rate for the 4A is actually limited to 7A by a little electonic thingy. Under normal conditions an RMG should never reach a max. draw of 7A.
Nigel Winkley
GER 87

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Post by Lester » 10 Sep 2009, 12:11

The RMG 'normally' draws around 1 amp. But when stalled, it'll draw 12 amps. I've melted my wiring insulation before now and pretty much destroyed the receiver, switch, harness, and NiMH battery...!
Lester Gilbert
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Post by Peter Allen » 10 Sep 2009, 13:15

So which of the two batts i've listed do you recomend i purchase,this is where i'm asking for help,the RMG 280ES is listed at 12A stall current,we sail in strong wind.Thanks Peter

Nigel
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Post by Nigel » 10 Sep 2009, 14:55

Peter,

don't worry about stall current. If you stall out over a lenghty period the batterie isn't the limiting factor. You will fry cables etc before and the batterie is actually protected against overload.

I have run the 1.350 cells for three days in my Marblehead in 3rd and 4th suit without any issues.
Nigel Winkley
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Post by Frednatal » 06 Nov 2009, 00:14

If I use the Life (6.6 V) for Futaba and Hitech servos (6.0 V) I need a voltage regulator or the servo accept this extra voltage?
Fred Schmidt

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Rob Guyatt
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Post by Rob Guyatt » 06 Nov 2009, 08:10

Hi Fred,
I aint no battery expert but know a bit about electrics so I hope I can help. It can get somewhat confusing when looking at servo specs and battery voltages etc. When a servo is specified at 4.8 and 6V this basically refers to 4 cells or 5 cells respectively. Those cells being either NiCd or NimH which are nominally 1.2V per cell. But they charge up to well above that. Fully charged a NimH or NiCd will be a bit over 1.4 V per cell. So a fully charged 4 cell pack is a bit over 5.6 and 5 cells are about 7V. When I was using NimH I found the 5 cell pack I used go to about 7.25V. I use LiPo for boat and Tx these days.

Likewise the same is for LiPo and the other Lithium based cells. The nominal voltage is not what they charge to. A 2 cell LiPo is nominally 7.4 but comes off the charger at 8.4.

The 2 cell LiFe will be about 7.6V fully charged. I am not sure but that might be a bit much for some servos. It's not much more than the 5 cell voltage I mentioned before but it is more so tread carefully. Make sure the servo is rated for 6V. Oh and make sure the receiver will handle the voltage too.

Lester made a point earlier that has me curious. He stated that he damaged a receiver after a winch stall. Assuming the wiring was the standard battery to winch then winch to receiver then the winch can only supply 1 amp to the receiver. All that stall current is flowing between battery and winch motor via the controller circuit. The only current in the receiver is whatever the receiver and rudder servo is pulling. That's usually less than 1 amp.

Peter was spot on about the 9V limit for the RMG winch. Plug in a voltage above that and it just won't run. It has software that stops operation of the motor if the supply is too high. Can't harm it (well it would if you plugged it into the house mains :shock: ) Would be nice to be able to run say 12V and have super speed and power but the motor would not last long.

So that means that 6 cells is the max for NimH and NiCd and 2 cells for the Li... cells.

A bit more about that 12 Amps. That is based on the assumption of 6Volts at the motor. If there's some black wire corrosion in the connectors or switch is corroded and or wiring too small then the current may not get that high. If the wiring is good and battery is say LiPo at 8.4V (very little voltage drop under load) then the current is close to 17Amps. It would be interesting to see what gives first. The current protection circuit in the battery or the stall protection software feature in the winch. Better if the winch shuts down first since the rudder will still be ok but if the battery shuts down then the boat can't even be steered.


Rob

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Post by Frednatal » 06 Nov 2009, 14:42

Hi Rob,
well, I will use A 3003 Futaba for rudder and a 5745MG Hitec for sails on my first IOM that I am making, boths specifications give a range 4.8V ~ 6.0V to then. But, may be that this voltage are assotiated with 1.2V cells. What is the ultimate voltage that they can be submitted?
My charger have a program that limits the maximum charge capacity to give to battery, and I was thinking if I can associate the charge capacity with 6V voltage, this is another thing to know: if we can do this association.
If I know the battery capacity at 6.0V I will can limit the charger for this capacity and for consequence the voltage will be 6V.
Another charger program is the battery identifier. When it reconizes the battery - Life - it displays the nominal voltage and we can change it. But if we assume that a Life cell is 3.0V instead 3.3V, what problems I will have during charging?
Well, these are typical problems and questions to a new product and it's use.
Now I am with a problem: I forget my life plugged with RX and now it is deeply discharged and the charger do not reconize it.
The charger has a program that requires a time to reconize it - 10 minutes is standard - and variable with the battery charge capacity and I am plaing with this now, because 10 minutes was not sufficient.

Thank you for your replay.
Fred Schmidt

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Post by Rob Guyatt » 06 Nov 2009, 23:36

Fred,
My advice on chargers is simple. Only use a charger designed to be used for a particular battery type on that battery type. Unless you really know what you are doing, do not just dial up a voltage and current on a charger or any power supply thinking this will work on a battery unless you really know what you are doing.

Rob

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Post by Frednatal » 06 Nov 2009, 23:44

About the battery identification problem by charger, caused by low voltage (2.3V), my friend Claudio Pelarin say me to charge the battery as NiCd until reach 5.0V (controlling battery temperature) and after, change to normal charge process like Life.
In 3 minutes they are with 5.0V (without any increase of temperature) and after, the charger recognize it.
Great friend.
Fred Schmidt

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Post by Frednatal » 07 Nov 2009, 00:03

Hi Rob,

I agree, but my charger can charge and balance Lixx batteries (and others).

Really, was my first time to use the charger, and happened this problem.

About my doubts about limit the Voltage in 6.0V and/or limit the charge capacity to obtain a final 6.0V, I saw, when the batteries are charging in normal process, that until 6.0V the battery was charged 800 mAh and the great increase in charge was in the range 6.4 to 6.7V (about 1200 mA increased) and this make impossible limit the voltage or charge to obtain only 6.0V, without great lost of total charge.
Fred Schmidt

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Post by Frednatal » 07 Nov 2009, 15:27

I have some conclusions about the LiFePO4.

Today I receive a e-mail from Bruce Simpson (RCModelreviews.com) about the supply of 6.7V or a bit more to servos Hitec. He says that he used 2 LiFePO4 cells in a range of Hitec servos since HS425BB through to the HS5955TG without any problem.
With JR servos: "Some JR servos get a bit jittery around neutral with the higher voltage when fresh off the charger"

About the weight of LiFePO4, my friend Claudio Pelarin says:

LIFE A123 2 cells, 2300mah (PACK with 3 wires - one is heavy for high charge/discharge) = 169g;

LIFE A123 2 cells 1100 mah (PACK with 2 wires) = 90g.

LIFE generic 2 cells 1300mah (PACK with 2 wires) = 90g.

LIFE c123 2 cells 650 mah (PACK with 2 wires) = 38g

For comparison we have:

Futaba NICd 4,8V, 600mah, with 1 wire = 89g;
Hidrimax NiMH 6V, 1450mah, with 1 wire =141g;

Pelarin say that he use 2 cell LiFePO4 for Futaba servos and receptor and he never had problems.

He says also that he charge theirs LiFes A123 2300 mAh with 10A and 3,7V by cell without any problem but the others he charge with 2A to 4A

Pelarin is a RC aircraft designer.

I see when charging my LiFePO4 that 55% of total charge is done in the range 6.4V to 6.7V, where he has 2000 mAh. At 6.0V his charge is about 800 mAh.

And more one thing: d'ont never discharge yours LiFe less than 5.0V
Fred Schmidt

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http://www.iomdesign.worpress.com
http://footybrasil.wordpress.com/

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