|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
Hints And Tips about selection and use of motors and speed controllers issue 09 FEB 2003
The following information will help you prevent problems when using high-current motors.
Contrary to popular behavioral treats, it is recommended that you simply read all operating instructions!
The recommendations in the chapter "Warning notes, cautions" and the chapter "Installation" should be followed strictly to avoid damages to the motor and/or controller and your wallet.
Especially in these schulze instructions you will find a lot of hints to use your controller reliably and safely.
Schulze herewith gives permission to freely print and distribute these instructions.
1st - Never exceed the maximum allowed cell count of your controller - the controller WILL overheat and the motor and/or controller WILL fail - if you are using BEC, it may fail as well so you may lose your plane.
2nd - Limit total power wire length to 20 cm (7.8") for a two lead wire, or 40 cm (15") for total wire length. This includes the cabling from battery to its connector (including the leads from cell to cell), from the connector to the esc, and from the esc to the motor.
3rd - Do use a connector set which can handle the peak currents with margin best is to use the connector pairs we recommend in our operating instructions for the permissible current ( e.g. if you use a 30 amp rated connector at 50 amps, you can damage the controller!!!).
4th - Never exceed the maximum allowed cell count of your motor and the matching reduction ratio.
5th - Never use one controller for two motors which are coupled mechanically.
Explanations:
ref. 1st - The max. allowed cell count depends on the max. allowed voltage of the power transistors used in the controller. If you exceed the voltage, the transistor "dies".
ref. 2nd - Leads and of course motors are inductive. In switching power supplies (e. g. a speed controller) inductors produce high voltage spikes (e. g. over 200 Volts) when the switching transistor is switched from ON to OFF state. A battery pack is able to clamp those high voltage peaks which can destroy your controller only when there is no or only very small induction between controller and the clamping battery.
Otherwise (with long leads) the controller does not "see" the battery and the high voltage spikes cannot be clamped - your controller gets more than the allowed voltage (see first point).
If you use an 18 cell controller with 18 cells, a spike has more "killing voltage" than a spike which is clamped by a 12 cell battery.
ref. 3rd - If you use connectors which are not suited for high currents they will become too hot because of its relatively high resistance. Hot connectors loose its spring force - even when you overheat the springs when soldering your cables on it. If you use the connectors in a car or boat you have an additional shock load on the connectors. For this reason, only bullet contacts with its multiple contact points are reliable in those models, others - good for electric powered aircraft - can not be recommended).
ref. 4th - the max. allowed cell count depends on the max. allowed power and rotation speed of your motor. If you exceed the voltage, the motor becomes overheated and/or the internal magnets depart from their mount by centrifugal force. Also you can damage the controller by the huge voltage spikes produced by the saturation of the motor.
ref. 5th - We do not recommend to use two motors on one controller (see oerating instructions). With separate props it might work, but surely not with the whole range of motors. But: If you couple one motor mechanically to another every motor produces other response signals to the controller because of its different angle of the magnets to the motor windings. This never works without problems.
For this reason we strictly recommend to use one big motor instead of two smaller motors.
Examples:
If you want to use 18 cells with a max 18 cell controller, you need an 18 cell motor and the total cable length (positive and negative wires and battery bars and connectors) needs to be less than 16 inches.
Butt (end-to-end) soldering techniques are recommended here. If you make up a pack with cell-to-cell connecting bars, then, with 18 cells, you have 17 bars with 0,75 inches each which makes 12,75 inches only for the bars. This is the reason that we urge you to use only end-to-end soldered battery packs. Otherwise, when you add your total cable length you will see that you will easily exceed the allowed maximum of 16 inches of cabling.
The next point is: If you were to use a motor with only about 5.7mOhm Ri (internal resistance) at 18 cells, then at motor start, the start-up peak current will have stored so much energy in the inductance of the motor that the voltage spike at switching off the motor can cause a voltage spike at the controller which can exceed the rated 30 volts of the power devices by a great amount (see to 2nd).
Also it is important that your connectors are rated for the currents, for instance in a high powered RC-car you need connectors for 80Amps or more!
We recommend the use of 3,5mm or 4mm gold plated "bullet" type connectors with multiple contact points.
Check the connectors frequently. If the contact force decreases, the contact spring was overloaded by the motor current!
Examples:
For 18 cells in a Emaxx you need e.g. a Hacker B50-14S.
A Hacker B50-8S is ok for 8 to 10 cells in an Emaxx, not for 18 cells (it will hit an unloaded rpm greater than 100,000 !!).
Recommendations:
for EMAXX with a Hacker motor:
with 8 cells use B50-8S (4613RPM/V) Max. 17T pinion / future-18.97F
with 10 cells use B50-12S (3033RPM/V) 18T pinion / future-18.97F
with 12 cells use B50-12S (3033RPM/V) 16T pinion / future-18.97F
or, with 12 cells use C40-11L(2727RPM/V) 18T pinion/72T main gear / future-18.61
best regards
matthias schulze and ulf herder
developing team of schulze elektronik gmbh overlo_e.htm