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[john44]

Do brushless esc run o/k on lead acid batteries?

john

[inertia]

SLA batteries are not very good at supplying large continuous currents such as those demanded by brushless motors. I would avoid using them for that purpose if it were me.
DM

[aeronut]

The ESC doesn't know or care what type of battery is feeding it, so yes, it will work.  One caveat is that most modern ESC's have a LVC (Low Voltage Cut) circuit that is designed around Nicad/Nimh or Lipo batteries, so they may cut off at the wrong voltage for an SLA battery. However, running a SLA battery too low is not normally an issue as long as it's recharged straight away. Also, as Inertia said, high currents are best avoided with SLA batteries. If you know your motor is going to be drawing low current, then it should work OK and you'll be able to take advantage of the increased efficiency of a brushless motor.

[Mad_Mike]

well yes and no it depends on the demand of the motor. let me explain. Say you have a standard mabuchi 540 brushed motor, then swapped it for a brushless type that puts out the same amount of torque and speed, the brushless would only use half the amps that the brushed motor would to match the same performance. Brushed motors are on average 34-40% efficent whereas brushless are closer to 90%.
At the same time if you put the same amount of current and voltage into a matched pair of brushed and brushless motors you would get 50% more power out of the brushless. 
So as an answer yes you can use sla's on brushless as long as the brushless motor isnt working too hard. You need to find out what kind of amperage the motor is pulling under load or maybe we could get a better idea if we had the specs of the motor and propeller.

[Netleyned]

If they are that good then surely brushed motors are not the way to go on a new build
If a pair fitted in lieu of brushed can give a longer running time at scale speed (as opposed to fast electric)
and the prices of motors and esc's are tumbling it would seem the way to go
Or am I missing something?

Ned

[john44]

Mad -Mike,
the spec,s are as follows:- the motor,s are 2x Vortex 35/48/939
                                                     running 2x 62mm 4 blade prop,s
                                           using 2 x Hobbyking 90amp boat esc,s
I was thinking of running them on a 12v 12ahr lead acid, but after the
reply,s to this post will now probably use NiMh
 
The above will be used to run a 1/12th Trent.

john

[Mad_Mike]

I think model boats is the only area of rc that brushed motors are still used

If a pair fitted in lieu of brushed can give a longer running time at scale speed (as opposed to fast electric)

Ned

Im not sure about a pair of brushless motors to replace 1 brushed, yes i suppose you could use 2 very small brushless motors in place of 1 larger brushed one but then there are single brushless motors that would do the same job.  It would be like using 2 seperate 1000cc 2 cylinder engines rather than a 2L 4 cylinder.
Its just that brushles you get more bang for your buck if you like. If you were to take 2 motors, 1 brushed and 1 brushless and they both had a matched performance output, put down on the work bench the brushless one would be physically smaller. If you were to select a brushless motor that was the same physical size as its brushed counterpart, run them both on the same voltage and amps, the brushless one would put out more power. This is why they are good for fast stuff.
For scale though where we dont need a lot of power, you can still use a brushless, its just that a brushless motor wouldnt need to work as hard as a brushed one, therefore use less current.
The downside to brushless is that they need an esc all to themselves as the commutation is done digitally by the esc not mechanically in the motor itself. 2 brushless cannot run off 1 esc. Brushed motors can drive directly off a battery, brushless cannot.
 

[Netleyned]

Mike, I meant swapping two motors or one motor as required.
I have two fishing boat projects which need  about 3000rpm
at the prop (brass 50mm four bladed).
Just wondered what the options were

Ned

[Mad_Mike]

what kind of voltage do you want to use?

[Mad_Mike]

Mad -Mike,
the spec,s are as follows:- the motor,s are 2x Vortex 35/48/939
                                                     running 2x 62mm 4 blade prop,s
                                           using 2 x Hobbyking 90amp boat esc,s
I was thinking of running them on a 12v 12ahr lead acid, but after the
reply,s to this post will now probably use NiMh
 
The above will be used to run a 1/12th Trent.

john

I cant seem to find anything on the internet about that motor other than the the first number is diameter, the second is can lenth and the last is the kv. I can only presume its an out runner judging by the prop size. Im not sure but to me that motor is a little undersized to take advantage of the brushless efficiency, probably why it has 90 amp esc's   itl need another oppinion.

[Netleyned]

I am open to suggestions
I have room for 2  6v 4.5Ah Sla's
Anything else will need more ballast.
Not a problem.
Long runtime at scale speed is the goal.

Ned

[john44]

I cant seem to find anything on the internet about that motor other than the the first number is diameter, the second is can lenth and the last is the kv. I can only presume its an out runner judging by the prop size. Im not sure but to me that motor is a little undersized to take advantage of the brushless efficiency, probably why it has 90 amp esc's   itl need another oppinion.

What motors would you suggest?

john

[Mad_Mike]

i dont know for props that big

[Mad_Mike]

I am open to suggestions
I have room for 2  6v 4.5Ah Sla's
Anything else will need more ballast.
Not a problem.
Long runtime at scale speed is the goal.

Ned

you i reckon you could use one of these, you need a motor around 600kv with the can dimensions similar to the prop size.
 http://www.hobbyking.com/hobbyking/store/__19023__Turnigy_G25_Brushless_Outrunner_610kv.html
possible esc
http://www.hobbyking.com/hobbyking/store/__7377__Turnigy_Marine_35A_Brushless_Boat_ESC.html
im not sure though maybe someone else should have a check to see if they think so with these

[Mad_Mike]

What motors would you suggest?

john

If the boat has allready been running on them with no issues, then continue with them. If you start changing stuff around theres no gurantees that the outcome would be better. It is common practice to go over the top with esc current ratings especially chinese esc's. I would suggest that you try and get find out what the current actually is. You only need a ball park figure, the simplest way to do this is to put a fuse between the battery and the esc. Then run the boat in the bath or whereever at full throttle. Using nimh batteries Start with a 10 amp fuse first, if it pops you know the current is high than 10 amps. Then try a 15 if that pops then go 20. If that pops go to 25, keep going up till the fuse no longer pops. Say it doesnt pop at 25, then you know that the current under continuous laod is somewhere between 20 and 25 amps.

[sparkey]

  Always use under rate fuses, a fuse will run on a current higher than what it is rated, what matters is the time factor i.e. 30 amp fuse will hold
a load  of say 35 amps for quite a long time, time to do damage to the esc. I always under rate the fuse for the esc ,it is cheaper to change a
fuse than to replace the esc.
Ray.

[grendel]

depends on the fuse type  - fast blow or slow blow, a fast blow fuse will blow the moment the current hits its rated value, where a slow blow might allow a quick surge above its rating, but would blow if that current was exceeded for more than a second or so. the slow blow allow for the startup surge from a motor, I would imagine that to protect the esc you would want the fast blow unless the esc have the capability to withstand the startup surge too.
Grendel

[john44]

Hi guys,
Mad - Mike you are right,the 62mm props are way too big.
I will look at alternatives.

cheers

john

[Mad_Mike]

how did you come to that conclusion?

[john44]

Hi mike,
I meant,too big for the size of the motor I have fitted.
I have been told to go for the Hobbyking 4258-500kv 1300w
they are more than up-to the job on that size prop.

cheers

john

[Mad_Mike]

i found this pdf file written by nick 75. It goes into great explanation how to select a brushless motor for scale models

[john44]

cheers, I have downloaded it for future ref.

john

[Guy Bagley]

i recently entered the brushless minefield setting up an interceptor from models by design, the multi  bladed brass props supplied with the kit were lovely and scale but when copuled to the  brushless motors i was using were  nearly useless....
 
( FYI   i was using 2 x 800 kv motors )
 
i selected a load of props  to try out and ended up with props half the size as set out in the kit,- and best performance was from non  scale 2 bladed props  - i get good performance and  reasonalble duration  at about 45 to 50 mins per  nimh battery pack....
 
if i really want the scale look i can easily swap props  when on display but once in the water you cant see the props due to the tunnels so for me... who cares... i'd rather go for scale speed and duration and non scale props...
 
 

[john44]

Hi guy,
what voltage are you running them on?

thanks Mad-Mike
having read that pdf file the motors I had fitted would be o/k on 6v
and upto 70mm prop. (kv would be too high on 12v)
The motors I have ordered should be even better on 12v & my 62mm prop,s

I am trying to find out what the scale size prop is,Contacted Poole & Whitby,
 but I am not having any luck.
so It will run on the 62mm scale or not.

john

[Guy Bagley]

12 volts normally....


( but i have an 18 volt pack if i really want to be a hooligan )