3S or 4S LiPo for Electric Starter.

[David Davis]

The insulation on the cables of my old electric starter is beginning to crack.  I see that lots of people are attaching/taping LiPos to their starter motors these days obviating the need for long cables so I was thinking of rigging up a LiPo to my old starter motor.

 

Do people use 3S (11.1 volts) or 4S (14.8 volts) LiPos for this purpose?

 

I'm afraid that I cannot give details of my starter motor because it's so old that the wording on the labels has worn off. I have another one in a similar condition which I could uses if I make a horlicks of the alteration. ?

[Martin Harris - Moderator]

I would go with 3S - you've lost any voltage drop in the cables and if it's an oldish starter, the lower voltage will be less likely to cause it stress.  I used to run my 24v starter on a 5S pack (converted from a cooked 6S pack) but when it eventually died, I started using a 4S that was past its best and it still works well at reduced voltage.

[Tim Flyer]

I will be interested in the answers here too. I bought a new geared starter motor from Just Engines last year and have been very happy with it . I bought it to upgrade from my basic Sullivan which struggled on my laser 200v . Initially I thought I might use lipos but found it has plenty of power just using my old 12v flight box battery. Just Engines also warned of the risk of switch damage if using lipos and allowing the starter to stall for any length of time. As the starter works fine on 12v I simply have left it at that. Lead acid batteries are gentle and maybe allow starter motors to last longer?

[Martin Harris - Moderator]

I think it's just the voltage Tim - I tried my JE 24v starter on 2 12v gel cell batteries in series and it often micro welded the contacts.  On a 5S lipo (nominally 22.5v) it did the same occasionally - I can't see any reason why the battery technology would have any impact other than through voltage drop but that would vary between C ratings on packs anyway.

 

4S lipo packs on these starters seem a good compromise.  Alternatively should you need more torque (unlikely with the 6:1 gearing in the HD version) and need to use the full rated voltage, a suitable capacitor/resistor in series across the contacts might help to reduce sparking - the contact is only a flat bronze or brass strip.

[Don Fry]

I use 4s. Two reasons.

I reckon;

the higher voltage gets the motor moving quickly, and so off the big current use. It’s kinder to the switch,

The battery goes longer between charges. I don’t push my luck, I charge to 4.05 volts every month, but rarely put more than a 4 hundred milliamperes back in. The low end voltage is so I don’t get worried about excessive cell damage. I don’t do storage regimes on these batteries.

 

I have two. The older is a cheap bargain basement unit, 4s, 20C, 3000 Hobbyking LiPo. Been in continuous use for 5 years. No issues.

The other is one of the little geared units, 4s, 65C (elderly battery), 2000 HK Graphene battery. In use for a year, no issues. 
 

Be aware, Just Engines say, use a LiPo, no warranty. But I have not had an issue with my stuff, and they are not expensive starter motors

 

[Tim Flyer]

Thanks chaps?

[Ron Gray]

I use 6s with a dead cell and a 5s with a dead cell on my JE 24v starter, not had a problem with contacts welding and more than enough oomph to spin all of my glow and petrol engines (up to 60cc).

[Bob Cotsford]

I used to find that a 3S LiPo or LiFe would start anything up to a .90.  I used the ones that had lost their edge for electric models.  One that gave 3 or 4 minutes flying instead of the the usual 6-8 still worked fine on a starter for months.

[Frank Skilbeck]

1 hour ago, Don Fry said:

I use 4s. Two reasons.

I reckon;

the higher voltage gets the motor moving quickly, and so off the big current use. It’s kinder to the switch,

 

 

Don, that's not how electric motors work, a higher voltage will try to make the motor turn faster and power is proportional to the square of the speed, so amps would go up by the same amount. Although different types of electric motor, in large motor industrial installations we soft start motors at reduced voltage to limit the inrush current and ease the load on the system. Starting currents can be upto 15x the normal load current, this is probably why JE recommend against lipos as they hold their voltage much better than a 12v lead acid battery, so the motor will draw a higher current on start up.

 

But my sweet spot for my starters (one direct and one geared) is a 4s LiFe A123 cell pack.

[Chris Walby]

I had a bog standard starter and it was just not man enough to start my Laser 180, so I bought a Just Engines starter (been totally disappointed with it, but more of that later). 

 

It needs to be run on a 4S to get the 180 to start and a couple of times the contacts have welded closed and just needs a tap (after pulling the lipo plug apart). If you are starting anything up to around 120 size just stick with 3S.

 

As we all know lipos are very different to lead acid batteries when it comes to internal resistance and ability to provide high start currents. IMO this is why lipos tend to weld the contacts up although this is a two edge sword in you use a tired lipo they don't the real kick they once had. I used to use a rather tired lipo as my starter and it sat around months do its job with no issues in all weather conditions. It seemed to be slowing up a bit so I popped it on charge in the clubhouse, stuck another lipo in and went flying. Imagine my horror after my flight and returning to the clubhouse to find an acrid smell and a very puffy lipos having vented on the charging bench. My mantra is if its not good enough to fly then dispose of the lipo. 

 

The Just Engine design incorporates a pin sat in a gear and on mine it kept coming out requiring the need to strip it, reposition it and reassemble. A right pain at the field so I carry a spare starter now and a chicken stick as some pants starter is not ruining my day. In the end I stripped it and engineered a proper solution.

 

  PS - One advantage of the higher voltage and lower internal resistance of the lipo it allows much greater torque from the starter, so for smaller engine there is a much greater chance of bending conrods.

 

Edited April 4, 2021 by Chris Walby

[Don Fry]

3 hours ago, Frank Skilbeck said:

Don, that's not how electric motors work, a higher voltage will try to make the motor turn faster and power is proportional to the square of the speed, so amps would go up by the same amount. Although different types of electric motor, in large motor industrial installations we soft start motors at reduced voltage to limit the inrush current and ease the load on the system. Starting currents can be upto 15x the normal load current, this is probably why JE recommend against lipos as they hold their voltage much better than a 12v lead acid battery, so the motor will draw a higher current on start up.

 

But my sweet spot for my starters (one direct and one geared) is a 4s LiFe A123 cell pack.

You may be right. But my theoretically overloaded starter remains starting, without any issues, after five years. It is a 12 quid e bay special. I don’t think the motor cares what power you put to it. 

I still reckon, a short, destructive switch closure, cold switch, causes less damage than the longer opening arc. And in our case, the opening arc has smaller amps, the back EMF, on a running motor makes it so, Ohms law applies.
Back in the day, I saw the national grid switches being opened and closed. 450 thousand volts. The opening of the switch was a much more spectacular sight. 
I see we agree, that a sweet spot is between, 13.2 v, LiFe, and 14.4 v LiPo.
 

[Nigel R]

I went with a 3 cell 2200 taped to a standard 12v starter. No problem in anything up to 20cc.

 

Best flight box upgrade I made in a long time. 

 

I also swapped the pump and glow panel to run from an identical 3s pack. The panel retains it's 12v pass through. I carry a converter to use the starter from the power panel. Then I always have a backup in case the lipo on the starter dies. 

 

Ps can confirm a 3 cell is plenty enough to bend a rod in a .40. Primed, forgot, primed again. Won't do that again in a hurry. 

[J D 8]

I have done the same as Nigel above. 2200 3S to an old JP Powertorque starter gets up to Enya 90 4 strokes going just fine.     Starter box now half the weight it used to be.?

Edited April 5, 2021 by J D 8
more info.

[Engine Doctor]

You could also consider using li-ion cells  from an old drill or tool battery. The cells are much more robust having metal cases . You will still need to fit a balance lead etc for charging and treat with caution as they can if mistreated be just as dangerous as lipos.

[Don Fry]

I read recently, any decent cordless drill, fitted with a starter cone,  will start motors. No idea how big a drill is needed to start what size motor. I had forgotten I was going to make a starter cone to test the idea. 
I thought at the time, is it necessary to stock a specialist starter when you already have a geared motor with a nice switch and grip, which also drill holes as a sideline. 
Engine Doctor rattle the brain cell

Edited April 5, 2021 by Don Fry

[J D 8]

        Most cordless drills, at least the cheaper ones would not turn at a fast enough rpm to be a reliable starter.

[Don Fry]

You may be right. My cheap  10 mm screwdriver/drill , sub £20,  does 1300 rpm, having looked. It has the torque, but 1300 rpm will only get a motor that wants to start to go. 
 

I think, ball park estimate, it would turn a 90  2 st. 

Edited April 5, 2021 by Don Fry

[Scott Edwards 2]

Time to confess my sins - Just Engines say not to use a Lipo on their starters, but I accept the risk and have had no problems in 5 years. I'm running their 6:1 geared starter on a 5S 2500 ma pack (21v) it will churn over my Laser 360 Vee happily, which struggled on 4S. I only use short bursts, and never let it stall.

[Martin Harris - Moderator]

My reading of the Just Engines advice is that they acknowledge that "under certain circumstances" the contacts can weld - and be released by dismantling by the user- and that would not be considered a warranty repair.  They don't say that the starter itself is not covered and I haven't spotted any statement saying that you mustn't use LiPos.  My switch stuck EVERY time I used 2 x 12v lead acid gel cells and only occasionally on a 5S LiPo.  I could always get it to release by flicking the switch a few times after switching to the LiPo.  They still market the battery holder enthusiastically which is fairly obviously designed around a LiPo battery.  If I needed ultimate torque from the full "rated" voltage I would experiment with some spark quenching circuitry.  My guess is that not many people have tried using 2 x 12v batteries with the ready availability of much lighter and more compact LiPo alternatives.

 

The typical Yuasa 12v 7Ah battery is rated for a 1 second burst of 210A and 45A for 1 minute so I'm not sure voltage drop would be as significant as might be assumed.

 

I'm afraid that in my experience, the switch is not really up to the job for "24v" operation - either 12S Pb or 6S LiPo, .It is useable but with the danger of occasional hiccups on 5S LiPo but it was a real pain on 12S Pb.  However, it works very well to start all my engines and I'm quite happy with it.  Yes - I have used it on little engines and haven't (touch wood) damaged one yet. I ALWAYS check for free turning first though. 

[Charles Smitheman]

For years now I have been using a 3s 2200 lipo with a normal starter (dont know the brand and forgotten where it came from!)

It will start a Laser 150. If reluctant from cold I turn the prop until it is balancing on top of compression before applying the starter.

 

The problem with starters is that they destroy smaller engines, which I have been playing with more recently. I have straightened many bent con rods on 20's and smaller (I take in orphans ?) So I made a mini starter with a B&S lawnmower starter motor. I removed the gearbox and turned up an adaptor which holds a bit of silicone tube of about 6mm id. I run this with two Lion cells. It starts anything up to a 20 easily, the idea being that the starter stalls in case of a hydraulic lock thus protecting the engine. I find the safest way is not to prime the little engines at all, but just to spin it with the starter until it draws in fuel itself. 

[J D 8]

 The thing with smaller engines [ I start down to 15's and have never bent a rod ] is not to press the cone hard on to the spinner so if reluctant to turn over it just slips.

  I wince when I see other modelers spine up the starter then jab it hard on to the spinner. NOT good.?

[Martin Harris - Moderator]

I habitually used a conventional starter on 1/12 scale combat models with .15s and .25s but before the "scramble" would prime the engine and flick it over by hand without the glow to distribute the prime and ensure a safe rapid start (more duration points).  No con rods were ever harmed in the process...

 

How many times do you see people simply apply a starter and start chewing the spinner with the engine obviously locked?  It's not surprising that Charles has a ready supply!

 

I usually start my small engines by hand though these days - not for reasons of preservation but because I don't think the geared starter that I use turns little engines fast enough.  I realised this when I had great trouble getting a little second hand OS20 FS to start after many years of storage...much head scratching as I could see no reason why it shouldn't go until I realised that the starter was actually holding it back.  A prime, a good flick and it starts first time on most occasions - although it has taken as much as 3 flicks!

[john stones 1 - Moderator]

I don't believe starters break engines, the bit holding the starter can, in all the years I've been flying only seen one engine broke, an O.S 120 pumper, stood watching and advised they would break it, a myth where a tool gets blamed for poor usage.

[Simon Clark]

For what it's worth, I have two Just Engines geared starters. One is the 4:1 gear ratio version with standard sized spinner cone and the other is the 6.5:1 version with the large spinner cone. I use both with 4S LIPOs that are detachable and held with a velcro strap and connected with an XT60 connector. The larger one is used for 20-33cc two strokes (petrol and glow) and the smaller on is used for everything else. With 4S they both have bags of power and work really well. I have tried the smaller on with 3S and this is OK in most cases BUT it does not spin the engine as quick and for one (and only one) of my smaller glows, it does not start as easily due to the lower speed.

 

I charge the batteries before each session and discharge to storage level between sessions. Do not be tempted to use old and knackered batteries as a starter actually puts quite a load on the battery - it is only in use for a few seconds and in a whole day of flying will only run for a very few minutes but when it is running, it takes a lot of current, so you don't need a particularly high capacity but you do need a reasonable C rating. At the moment, I am using Turnigy 4S 1400 65C to good effect.

 

Simon

[David Davis]

Thank you for all of your advice gentlemen. I'll let you know how I get on.