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I recently performed Li-Po surgery on my motor.


custom-vince
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I have only had a week of testing so far but it looks promising, I know other manufacturers also use Li-Po batteries for their electric starts.

I swapped out the existing 9ah Sealed Lead Acid Battery which weighed in at 2.6kg (2600g) and fitted a Li-Po which produces 110amps peak and 60 amps continuous at 14.8v which weighed in at 198g (0.2kg) saving me another 2.4kg weight. And boy does this battery crank over, its blistering perfomance. I have calculated that I should get some where around 100 starts before it runs out. I have a computer controlled charger and charge it in situe within a vented titanium box. Battery temp has remained low though out.

(I have seen li-po charge bags??? not sure about them)

Its all looking good. My only concern now will be burning out the starter motor.

What have been peoples experiences with running 14.8v li-po through their starters.

Once I am happy with testing I will be offering an upgrade to any current Custom Air Cruiser owners, with a list of pros and cons to both systems.

Any questions or sugestions???

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I have been trying to figure out if it would be possible to rig on-board charging by running the output of the generator through a fat blocking diode and then onto a suitable charging circuit. A second diode would then be used to carry all discharge current other than direct starter motor feed. This I am thinking would mean that all current flowing into the battery would have to be via the charger, and that all current flowing out would NOT be via the charger. Sort of like two parallel one way streets in opposite directions.

There is of course the fire concern, and that does trouble me. I suppose I could just resort to a total loss system like yours vince. The generator output could be utilised to run any other on board electrics, just not a charge circuit.

Phil

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I have only had a week of testing so far but it looks promising, I know other manufacturers also use Li-Po batteries for their electric starts.

I swapped out the existing 9ah Sealed Lead Acid Battery which weighed in at 2.6kg (2600g) and fitted a Li-Po which produces 110amps peak and 60 amps continuous at 14.8v which weighed in at 198g (0.2kg) saving me another 2.4kg weight. And boy does this battery crank over, its blistering perfomance. I have calculated that I should get some where around 100 starts before it runs out. I have a computer controlled charger and charge it in situe within a vented titanium box. Battery temp has remained low though out.

(I have seen li-po charge bags??? not sure about them)

Its all looking good. My only concern now will be burning out the starter motor.

What have been peoples experiences with running 14.8v li-po through their starters.

Once I am happy with testing I will be offering an upgrade to any current Custom Air Cruiser owners, with a list of pros and cons to both systems.

Any questions or sugestions???

I believe flat top Dave posted something about these a while back, I have thought of fitting one to my pap but am just concerned about the charging/venting element.

do you need a special charger?

Dave.

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I wouldn't have thought the risk of motor burnout is any greater with LiPo's - remember that motor current draw is determined by torque requirement i.e. makes no difference what the motor battery type is, it's still going tio draw what it needs, and both Pb/LiPo/NmHydride/NiCad can all be be configured as +/- 14Vdc battery packs to prodive sufficent cranking Amps should the commutator or engine "jam" to burn out the starter coil - likewise any of these battery technologies can be configured Amp wise to not deliver more than a certain amount of Amps.

In short: if concerned about the LiPo's been able to provide suficient current to burn out the starter coil, you have 2 options: rebuild the LiPo pack using lower Amp output LiPo cells, or fix a slow burn in-line fuse on the + positive wire - rated for whatever time/Amp relationship you feel is appropriate.

The big advantage with LiPo's of course is their huge power density ratio - massively so when compared to Pb "bricks". The discouragement to date has of course been their finiky charging requirments - but both those issues are now no longer the problem they were when LiPo's started to become commericialy vaible - chargers which can run off alternator type outputs can be sourced easily from the UAV industry, and to a lessor extent from the large scale model R/C industry (where my hobby experience with LiPo's lies).

Heres my "possible" concern using LiPo's on PPG's - but please note: this concern is theoretical - my experience to date with PPG's is limited to theory (just getting into the practical side of things): it's the constant vibration. LiPo cell's are delicate and long term repeptative vibration can in theory upset the cells - but its nothing I wouldn't think a decently consturcted cell pack couldn't deal with (e.g. wrap them up in Sorbathane or some similar good damping material).

Lastly, if you haven't done this I would strongly reccomend it: ensure that every cell in the LiPo pack has it's own individual monitoring circuit - again, a component that is easily sourced from the scale model R/C industry - this will ensure charging/discharging never exceeds the individual cell parameters - the last thing you want is LiPo pack going up in flames on your back at 1000 plus ft AGL!!!!!

To answer your question re: charging bag: again - any decent R/C model dealer will have them in stock for a whole bunch of sizes - if you come unstuck, drop me note with your LiPo pack dimensions and I'll source one for you.

Not to make too fine a point of it - just in the off chance you don't know (but I'm sure you do): USE ONLY A LIPO CHARGER FOR YOUR PACK AND MAKE ABSOLUTELY 101% CERTAIN IT'S CHARGE/DISCHARGE PARAMETERS, OR SETUP (as with multi voltage LiPo pack chargers) ARE APPROPRIATE FOR THE CELL AMPERAGE SPEC AS WELL AS THE PACK VOLTAGE SPEC'S - NOTHING, BUT NOTHING ELSE WILL DO

Chris

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I have seen suitable Li-Po chargers that are small enough to fit inside the battery box and could run off the alternator. It was something I was looking into.

But for the reasons of cherging stability, I decided to go with the larger temp sensitive cell monitoring charger and then it is only charged when not in flight via the car or mains.

Once I fitted the Li-Po and worked out that 1 charge will last for many starts I just dispelled with the need for inflight charging as an unnecessary risk right now.

It is so light that I fitted it using large velcro pads which also absorb some vibration.

Whats the view on the safe charge bags?

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I have had some experience of lipo's for rc heli stuff but unless they have got better since... I would avoid them.

If they get damaged they have a tendancy to pop/explode also charging is a bit dodgy ! If one cell gets over charged then the batterys are screwed, also if they drop below 3.2v per cell (I think?) then the life span is badly affected so get a voltage warning light.

Tom :acro:

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.... which is why I said in my above comments that each cell should have a "monitoring circuit" attached - which will ensure charge and discharge parameters cannot be exceeded.

Charge Bags - safe or not? - yes, that is after all what they designed for. I would say use one - both on the ground (especialy if charging in your car ore house), and in the air (will save you having to deal with a fire in the air in the unikely event of cell/pack failure). The added weight/mass is only in grams. LiPo battery pack has a power density of between 0.50g/cm3 - 0.54g/cm3. A Pb battery (Lead) has a power density of between 11.1g/cm3 - 11.3g/cm3 i.e. the weight/mass saving is some 20 x better than Pb's. Adding a safe charge bag is an insignificant additional weight/mass wise - use it.

Popping/Exploding if damaged? - yes, they certainly will - it is important they are packed properly and securely.

Charging - use anything else other than a LiPo charger, set to charge within the manufacturer charge spec's and at best you'll just render the pack useless within a few charge/discharge cycles, and at worst you have an explosion of fire on your hands.

Overall, so long as one follows the rules using LiPo's and treats them correctly, they are now pretty much as safe as NiCads and Pb's - I certainly will be using them on whatever PPG I purchase in due course.

Outkast - you are asking in respect of LiPo battery packs? Can you tell me what the voltage of the battery pack is (standard 12Vdc - 14Vdc?) and what the Amperage (in milliAmps or Amps) of the battery pack is? Is this a charger you want to run off the alternator on the PPG, or off your home AC mains supply, or off say your car battery on a day out?

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Do I need a discharge monitor circuit for when I am using the battery or will my balance charger cover my needs (Turnigy Accucel 6S lipo charger)

I am using RcBatteries 25c Li-Po pack 4S1P

Spec: Capacity: 2200 mAh, Voltage: 4S1P 14.8V, Discharge Rate: 25C (55A) Continuous, 60C (110A) Burst, Weight: 220g (actually weighed slightly less), Dimensions: 30x35x105mm

I will get a charge bag after watching that video. Battery in charge bag, inside titanium box. Only gets used for a couple of seconds each time when starting the motor, so I dont feel I need to worry in flight.

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Do I need a discharge monitor circuit for when I am using the battery or will my balance charger cover my needs (Turnigy Accucel 6S lipo charger)

I am using RcBatteries 25c Li-Po pack 4S1P

Spec: Capacity: 2200 mAh, Voltage: 4S1P 14.8V, Discharge Rate: 25C (55A) Continuous, 60C (110A) Burst, Weight: 220g (actually weighed slightly less), Dimensions: 30x35x105mm

I will get a charge bag after watching that video. Battery in charge bag, inside titanium box. Only gets used for a couple of seconds each time when starting the motor, so I dont feel I need to worry in flight.

Yes and No:

No if are in the habit of recharging after each day out flying - I really can't see a situation on a day by day basis (wuth charging at the end of each days' flying) which is going to lead to your LiPo pack been discharged excessively - you'll be wondering what the hell is going on if you are having to crank the motor over so much to start it that it is running that pack flat.

Yes if are wanting to only recharge when required - and to establish when recharging is required, something along the lines of the info attached below will do the job - the dealer/seller is:

www.revolutionmodels.co.uk/acatalog/Accessories_for_Electrics.html

1) Li-Po Battery Management Unit 234(Reference #539)

2) Li-Po Battery Management - 5678 High Voltage(Reference #607)

3) Li-Po Battery Management - 9012 High Voltage(Reference #602)

4) Spartan G4 Li-Po Guard(Reference #981)

Wire any of the above into the battery power circuit permanently - unlike the Turnigy of course which is only connected when charging.

All of the above can be set-up and configured to warn you (with audio and/or sound) when your LiPo pack is approaching its lower state of safe discharge. I have no association with the manufacturer or dealer of these products - just familiar with them and they have worked reliably for me - and for what they do, they are priced right - oh,, and they only weigh a few grams.

For some good info on LiPo cells and packs, answers to questions, batteries avalible, charging/discharging, comparisons, custom LiPo packs...ect ect ... scroll through the headings on the left hand side of the home page of:

www.powerstream.com

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Thanks I have just looked at them.

The first one goes to 14.4v and I am using 14.8v I guess its not ok.

The 2nd and 3rd are for larger batteries I am 4s only. or do they cover smaller batts also.

the 4th doesnt say much. but has only 2 wires

Am I right in that they are all only visible / audible volt meters, and not individual cell balancers? Do I need discharge cell balancer?

I already have one of these meters below which gives me individual cell voltage. and then a total.

http://cgi.ebay.co.uk/ws/eBayISAPI.dll?ViewItem&item=190332489631&ssPageName=STRK:MEWNX:IT

When do li-po's burn? when over charged or shorted out.. any other time?

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Thanks I have just looked at them.

The first one goes to 14.4v and I am using 14.8v I guess its not ok.

The 2nd and 3rd are for larger batteries I am 4s only. or do they cover smaller batts also.

the 4th doesnt say much. but has only 2 wires

Am I right in that they are all only visible / audible volt meters, and not individual cell balancers? Do I need discharge cell balancer?

I already have one of these meters below which gives me individual cell voltage. and then a total.

http://cgi.ebay.co.uk/ws/eBayISAPI.dll?ViewItem&item=190332489631&ssPageName=STRK:MEWNX:IT

When do li-po's burn? when over charged or shorted out.. any other time?

Give me a couple hours - I'll post up on the forum some specific for your battery pack this evening.

To answer your question: its not that striagth forward - some conditions/parameters would need to be defined to assess the risk of burn out, however:

- they are at risk of burning if they short - but the dump currents are so high from LiPo's that you'll find in almost all cases, unless the cable/tag connected to the pack is really very thick, the cable/tag connected to them will heat up like a heater element and then melt - which will then stop the current flowing.

- overcharging: batteries (immaterial of battery type) tend to only draw from whatever charger they are using, the current that they need, and which the charger is capable of delivering. In theory while its a possibility, a LiPo charger is unlikley to cause a LiPo pack to burn - but it can happen if the charge parameters are not setup correctly on the charger for the Amp/Voltage of the LiPo pack (which is why it is so important to use the correct charger for LiPo packs.

I'll post up this evening for you some links to exactly the monitor that is appropriate for your LiPo pack.

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Much appreciated. Thanks. Have been learning as I go. I left electric models just as Ni-Mh was coming in.

Custom-Vince

The first one (i.e. Li-Po Battery Management Unit 234(Reference #539) is suitable.

The 0.4volts difference you refer to can be beause of one of 2 reasons:

- different LiPo cell chemistry

- different way of referencing the individual cell voltages

LiPo cell chemistry difference – different LiPo cell manufacturers use different cell chemistries, but charge/discharge log’s across the different commercialy LiPo cell chemistries is for all intents and purposes the same – with a few exceptions (e.g. Lithium Iron Disulphide), and when these cells are sold to end users there is usually documentation with them that says WARNING …. Blah blah, blah blah…… i.e. you'll know it if you get hold of a rechargable Lithium pack that requires special charging/discharging.

So although there may be slight differences between manufacturers, the differences are so small that unless you choose and use a rechargeable Lithium battery cell chemistry that is unusual, you can negate the small 0.X V differences - so long as you make the distinction between Lithium Ion and Lithium Polymer – the 2 dominant Lithium cell chemistries now commericaly avalible and sold through retailers for the R/C market.

In short: a LiPo charger capable of charging x amount of cells will be compatible with all the LiPo cell chemistries – and any accessory made for a LiPo pack of x amount of cells/volts, is going to be compatable with all manaufacturer LiPo cell’s packs – irrespective of manufacturer or 0.X differences in pack voltage(s) – so long as you are comparing packs on a like for like basis (i.e. same amount of cells in the pack, same size cells in the pack).

…….. that’s a mouthful – sorry, but I’ve had to choose my words carefully here to ensure what I was writing up was as accurate as it need be, and most importantly – safe info.

Here are some more monitors that you can use with your LiPo battery pack – they are all suitable for 4S packs of the total milliAmps:

www.espritmodel.com/index.asp?PageAction=VIEWPROD&ProdID=6346

http://www.radicalrc.com/shop/?cat=45

Custom-Vince - read the following article – will give you a good understanding of LiPo’s

www.fmadirect.com/lipo_handbook/FMA_Lipo_Handbook_Section3.htm

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