Temporary ESC fail

[Ken Banks 1Participant @kenbanks1]

I have made an experimental model trimaran to my own design using polystyrene insulation powered by an air propellor.

Power is supplied from a 12V battery pack of 10 Ni MH 1.2v 2600 mAh cells to a 540 brushed motor turning a 6 x 4.5 twin blade propellor. The ESC is a 320A 7.2 – 16V bidirectional unit with cooling fab and 5.6V 2A BEC.

The motor runs fine at cruising rpm but under greater power, the ESC cuts out but restarts immediately if turned off / on.

To reduce apparent battery drain I removed the red power wire from the ESC / receiver lead and supplied separate power to the receiver from a Ripmax Sanyo 4.8V battery pack.

Disappointingly, this did not resolve the problem although I suspect that the receiver pack may the culprit in being of insufficient voltage for the ESC or not sufficiently charged. Unfortunately, I do not know how to test the receiver battery pack via its tiny Futaba plug.

Seems that the motor battery capacity is inadequate under load and is reducing available voltage below the ESC requirements despite a separate feed to the receiver.

Should I increase the main battery to 16V or uprate the receiver pack to provide 7.2V …. or is the (assumed) oriental ESC the problem?

I hae a tug with the same ESC using a 12V lead acid battery and this runs faultlessly. However, a LA battery would sink the trimaran.

Kenb

New member

[Ken Banks 1Participant @kenbanks1]

Esc cuts out underload

[John W EParticipant @johnwe]

Could it be that the prop is too big? and the motor is drawing too many amps with this big prop on and causing the speed controller to overload and shut down? Sounds as though you may have a Chinese speed controller with that size amperage?   Never trust a speed controller ratings from the East – We know all about them and the magic smoke – If there wasn't enough guts in the batteries it would just slow down and then shut off. Just a thought.

 

John

Edited By John W E on 17/03/2019 18:24:00

[Ray Wood 3Participant @raywood3]

Hi Ken,

From my early electric flight days in the mid nineties we were using brushed 600 motors on 9.6v nicads. and 40amp speed controllers turning 9×6 props , I think your expecting a lot from your poor little 540, if your trying to break the sound barrier i,d go brushless with 11.1v lipos 3 cell battery .

Regards Ray

[Dave MilbournParticipant @davemilbourn48782]

I would initially have suspected a faulty cell or cells in the 12v pack which is/are dropping well below 1.1v when the current drain is high. First, however, I'd point the finger at that ESC – largely because those '320A' ones are known to be trouble. In a tug it's probably only supplying a few amps but a 540 motor with an airscrew is a different matter altogether. That 320A rating is almost certainly for the instantaneous surge current and the realistic continuous current rating will be much, much lower. Unfortunately there's no way of knowing what the true value is; my guess would be no more than 15A.
I'd try a different make of ESC with a known, reliable maximum continuous current rating and also use a wattmeter to monitor the current and voltage. There are numerous cheap ones on the Internet – this is the one I use **LINK**

Dave M

[Written before John's and Ray's postings hit the board. A brushless motor and a 3S LiPo pack would solve the problem, as Ray says]

Edited By Dave Milbourn on 17/03/2019 18:41:20

[Colin BishopModerator @colinbishop34627]

To start a car you need around 200 amps from the battery so, as Dave says, the 320amp ESC rating is meaningless for all practical purposes. It's the continuous current rating which matters. Plus of course the quality of components and construction. As always, you get what you pay for.

Colin

[Ken Banks 1Participant @kenbanks1]

I'm grateful for the advice from everyone. All the points made seem salient but the finger of blame seems squarely pointed at the wily oriental ESC.

I'm amazed to learn that an the air propeller (which I hadn't previously considered large) consumes so many amps compared with those required by my tug which I would have thought needs vastly more effort to push through water.

Unfortunately I'm not in a position to go brushless at present. ! have another tug which has a 12 volt lead acid battery and a Viper Marine 15 ESC. Does this have a continuous current rating of 15 amps and is it likely to be adequate?

Dave recommends a wattmeter. Can the receiver battery be tested with this.

Many thanks

Ken

[Dave MilbournParticipant @davemilbourn48782]

Ken

The MTroniks ESC is rated at 15A continuous but may well not be enough for a 540 with an airscrew. Frankly you'd be better off with a cheap, forward-only ESC designed for model aircraft. Here's one chosen at random **LINK**
The wattmeter I showed is intended for large NiMH/LiPo batteries with Deans connectors and not 3-pin Futaba type Rx plugs. The best way to test that battery is to connect it to the Rx and a couple of servos, then measure the voltage across a pair of spare Rx input pins while you operate the Tx sticks to move the servos. If you only have a 2-channel Rx then just connect one servo. Like this:

A fully-charged Rx pack will show at least 4.8v under load. Any less and it's bin time.

Dave M

[Malcolm FraryParticipant @malcolmfrary95515]

Do not be surprised that airscrews soak up power – some Merlin engines coughed out 1600 HP to drive their airscrew, a flower Cass Corvette had only a bit more to drive itself. Later Spitfies used a Griffon that coughed out nearly 2500 HP.

When you look at the wiring fitted to a "320A" ESC, you should figure that the "320" is either a decorative mark or total optimism. Many were sold as lower voltage types, the higher voltage variant looked much the same but had a cooling fan.

It is possble that the battery is not supplying the needed current at full power and the ESC is spotting the volt drop and cutting out, needing a power off reset to come back to life. Overheating might have exactly the same results.

When selecting an ESC, if a meter is not available, a box of assorted fuses helps. Find the top value that blows, take the next value up, look for an ESC that is known to handle more than that. Generous derating is a good, valid, engineering practice. Apart from that, what Dave just said above.

[Ken Banks 1Participant @kenbanks1]

Hi Dave

Very many thanks for your valuable advice esp. regarding testing receiver battery pack with Futaba plug.

The main battery is a 10 cell pack 12V from the Component Shop bought a couple of weeks ago. Later today, as an experiment, I'm going to attach the 12V 3AH sealed lead acid tug battery as a temp. replacement but still using the separate receiver battery and bench test.

I'll let you know what happens.

Cheers

Ken

[Dave MilbournParticipant @davemilbourn48782]

Ken

For General Info –

Many people believe that when they buy a new rechargeable battery it's already fully-charged. It ain't. There's some charge in it – the amount depending on how much was put in to start with and how long it's been on the shelf since then, quietly self-discharging. My advice is always to give a new pack a charge at one tenth of its C rating [which is 1/10 x 2.6A for a 2600maH pack = 260mA] for 14-16 hours, then use this charge rate for several subsequent charges before you attempt to fast-charge it. Also NEVER charge at more than the C rate. Despite what you might read, like Corporal Jones' fuzzy-wuzzies, they don't like it up 'em.

BTW just to illustrate what Malcolm said, 320A at 12v is getting on for 4 kW. You'd need wiring about as thick as your finger to take that amount of power!

Dave M

Edited By Dave Milbourn on 18/03/2019 14:56:21

[Malcolm FraryParticipant @malcolmfrary95515]

Finger thick? More like a premium pork sausage, maybe one of the "Snorkers" mentioned in "The Cruel Sea"? . 320A would probably put bits of the supplied connectors into orbit.

[Dave MilbournParticipant @davemilbourn48782]

Ken may have thick fingers, Malc, but I think the message got through that 12 or even 14AWG isn't quite the ticket for 320A. Frankly I wouldn't go near one of those 320A 'Blue Meanies' at any price and I'm surprised they haven't been banned under the Geneva Convention. Certainly they're not quite 'in step' with any acceptable advertising standard I can think of.

Ken
Take a look at the cable which earths the battery in your car to the body. That would just about stretch to 320A @ 12v, but not for very long!

Dave M

[Ken Banks 1Participant @kenbanks1]

Hi Dave and Malcolm

Thanks once again for your detailed advice.

Regarding the charging of 'new' rechargeable batteries, I do take your point from past experience. I bought the Universal Charger from the Compo. Shop when I ordered the 12V battery pack and fully charged it before use. However, I'll abide by your advice when I buy more. Eat your heart out Cpl. Jones.

HOWEVER

As it mentioned earlier, I hooked up the 12 SLA battery and, to my great delight, the ( seemingly much maligned) Beast from the East performed admirably on full chat and has since shown no sign of faltering! True test will be on New Brighton Boating Lake when the wind abates.Your further comments welcome.

I can't use the SLA as it is far too heavy. The question now is how can I replicate the performance of the SLA battery with rechargeable 1.2 cells. Attach another 10 parallel perhaps?

Ken

[Dave MilbournParticipant @davemilbourn48782]

Ken

It's likely either a faulty cell in the 12v pack or a duff charger. One would expect both to work properly from new.
If it fails again I'd contact CompShop and request a comment from them and insist on replacements if necessary. Mucking about with trying to identify a faulty cell in a new pack of ten isn't reasonable if you've followed the charger's instructions correctly.

Dave M

[Ken Banks 1Participant @kenbanks1]

Hi Dave

Thanks for your continued interest.

Does not the fact that the 540 motor runs continuously without hesitation when fed by the lead acid battery indicate that the Chinese ESC is functioning as it should?

Ken

[Dave MilbournParticipant @davemilbourn48782]

Quite so – hence my comments about the charger and battery pack.

DM

[Malcolm FraryParticipant @malcolmfrary95515]

In the spirit of experimentation, it might be instructive to look at the battery volts under load. Compare the SLA performance with the NiMH pack, remembering that the battery is not just the battery, its all the wiring and connectors that the current goes through before the ESC. A slightly dodgy connector might produce the symptoms. One of the reasons why Tamiya connectors are held in low regard.

[Ken Banks 1Participant @kenbanks1]

Hi Malcolm

Not sure how to test voltage under load as there does not appear to be any access for the voltmeter probes. I'd be grateful if you could explain how to go about it with the (dreaded) Tamiya connectors in place. All equipment is new and all connections appear firm.

Also bit confused by the performance difference between the (new) 10 cell 1.2V 2600 mAH (understood to be 2.6AH) battery pack – and 3AH SLA. Presumably the lead battery has a considerably greater operating capacity – although only by 0..4 AH.

If I added another 10 cell battery pack in parallel, would this be the way to go to emulate the SLA's output?.

Ken

[Dave MilbournParticipant @davemilbourn48782]

Ken

The 'usual' type of SLA battery has a capacity of 3AH only if the current drawn is low i.e. milliamps. As the current increases – typically to that required by a fairly modest electric motor – the capacity rapidly decreases. There are things called leisure batteries which are Sealed Lead Acid and intended for such applications as golf trollies and mobility scooters, but they aren't the type generally sold to modellers. These would typically have a capacity of >20AH and a price, weight and size to match. **LINK**

A 2600maH NiMH pack should be able to deliver that capacity right up to C rate, when it will decrease markedly as the current increases. There's a learned treatise written in English for non-tech speakers here **LINK**, albeit a bit dated now. At the present time there are 5000maH NiMH and LiPo packs which will both deliver 5000maH reliably. I would repeat my opinion that SLA batteries are terrific for ballast and workshop weights but as power sources for motors they belong back in the 1960s.

As for Tamiya connectors – what he said.

Dave M

[Colin BishopModerator @colinbishop34627]

As Dave says, Lead acid cells are very much yesterday's technology now. The actual capacity is only around 50% of the nominal capacity. For relatively sedate models NiMH are the way to go as they are simple to install and operate and you can usually use most of the nominal capacity so they are effectively much more efficient than lead acid plus the weight is lower in the hull which improves stability. For extra performance then LiPo is what you want with a bit of extra care in looking after them. As always, horses for courses.

Colin

Edited By Colin Bishop on 19/03/2019 19:33:12

[Ken Banks 1Participant @kenbanks1]

Many thanks Dave and Colin for advice and links.

Interestingly, at the Wallasey Model Boat Society, of which Dave Wolley (a regular article contributor to the Magazine and forum) is a member, the 12V SLA is regularly used in many boats together with the wicked ( but now seemingly exonerated ) Chinese ESC. The combination apparently works very well in apparent contradiction of the views expressed. My own tugs, and now my experimental trimaran, are examples.

I hadn't employed a SLA in the small trimaran purely because of its weight so the issue would seem to revolve purely around the output 10 cell NI MH battery pack. As Dave suggested, I'll relay the problem to the Component Shop for comment. Doubtless they will blame the ESC!

Ken.

[Dave MilbournParticipant @davemilbourn48782]

Ken

I'm sure it's the case that lead-acid batteries are still used in models with conventional props and low current-consumption motors, but your original query wasn't about such an application. Similarly a speed controller which claims to have a current carrying capacity of 320A should at the very least be able to cope with the 2 – 3A drawn by such motors. That the type regularly fails at higher currents – and would have no possible chance of withstanding a current of 320A in any event – is also a matter of record. I've either handled or witnessed maybe ten that have done so when connected to 540/600 motors and run on 6 – 8 NiMH cells. I wouldn't purchase a unit with such dubious claims made for it and I wouldn't recommend anyone else to do so. Still, it's a free country – 'caveat emptor' not withstanding.

You might refer this correspondence to Component Shop to support any contention about the problem.

Dave Milbourn

Edited By Dave Milbourn on 20/03/2019 10:26:30

[Malcolm FraryParticipant @malcolmfrary95515]

Access for testing electric. Since many years ago, manufacturers have sought to severely limit access to live electricity to the paying public, hence the shrouded connection plugs and line sockets. From the safety point of view, quite reasonably. The drawback is that this also restricts the ability to get to anything that needs testing, not helped by the meter manufacturers also making "safe" probes.

Possible solutions to measuring the battery voltage are an interrupt lead (basically a short extension with an access socket added as a Y lead) or pins and clips to allow a meter to connect to the metal bits. Having experience in the field, I know how to do this kind of thing and keep my finger ends and eyebrows, I would not reccomend it to anybody who needed to ask. Some ESCs "might" allow access to their battery connection terminals, but most will have them safely sealed away.

Battery voltage testing needs to be under load – a dud cell can show the full expected voltage, but have very low capacity. Under use, it will seem to work OK briefly, then the ESC "might" spot a sudden volt drop and go into its panic mode. Switching off and back on "might" allow the dud cell a bit of rest and recovery to create further confusion. Even the brief time between failure and disconnecting to measure can result in a false reading. Testing on an airboat should be simpler – everything under test can be indoors in the warm and dry, no test tank needed to provide the load.

SLA are usually quoted at the "10-Hour Rate" , so a 3AH battery should be good for 300mA for 10 hours. A slightly larger AH figure can be got for the same battery by quoting a "20-Hour Rate". SLA were widely used back then because they were the only game in town, and their shortcomings were tolerated because there wasn't any real alternative. I remember "Nike" cells. Nasty, bulky things, and you needed to find a friendly chemist who was prepared to sell you a bottle of 20% potassium hydroxide solution to fill them with. Running SLA at a higher discharge rate reduces their efficiency. It also cuts into their life expectancy, but this is true for all batteries.

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