series paralell switch 3

[blacktop]

I have a 36volt dc motor powered by three 12 volt 60 amp.hr. deep cycle batterys. I want to start this motor on 12 volts, then switch to 24 volts then onto full power to 36 volts. this would give me a "soft start, sort of" how do I connect up the 3 batterys via a 4 way switch. I do not wish to use electronics to give variable speed control.

 

[fsmyth]

Simply connect the batteries in series, connect each
positive terminal to a pole on the switch, the motor(+)
to the wiper, and the motor(-) to battery negative.
Make sure that the switch is break-before-make, or you
will be replacing it.
<als>

 

[blacktop]

the switch is make before break [rotary] not sure what you mean by "the motor + to the wiper"

 

[blacktop]

the last post should read break before make. regards from nottingham uk

 

[fsmyth]

I assume that you have a 4PST switch. In which case, you
will have 5 terminals; four of them will be contacts, and
one will be the "OFF" position. The remaining terminal is
the movable contact, or wiper.

 

[itsmoked]

I sincerely hope you will be charging all those batteries individually with floating chargers or you will destroy them quickly.

You will be overly discharging the low speed battery and the high speed battery won't be discharged as much.

This is why people use speed controls... To NOT thrash their batteries.

 

[ScottyUK]

itsmoked is correct - the better solution would be to use a PWM or chopper controller to vary the speed. These are available with very low losses, and some have ability to regenerate energy stored in a rotating load back into the battery under deceleration. The following link might prove enlightening:

http://www.4qd.co.uk/faq/

If you do intend to persist with the switching scheme, consider using your switch to control power relays rather than bringing high current to the selector. I'd be avoiding anything over a few amps going through the switch. Also check the switch or relay ratings for DC service - DC with an inductive load is particularly hard on the switch or relay. Your low voltage works in your favour though.


----------------------------------

One day my ship will come in.
But with my luck, I'll be at the airport!

 

[blacktop]

thanks for your reply. the 36volt motor will start on the 1st. battery, 12volts, then instantly switched to two batterys in series giving 24 volts, then switched to the three batterys in series giving 36 volts. A 36 volt floating charger will be used for re-charging. the three batterys will run the 36 volt motor for 99% of its run time.I have used the same system on a 24 volt motor using two 12 volt batts, starting on one battery then switching to 24 volts. This has run a three wheeled electric trike. I have driven this many hundreds of miles, my weight 230 pounds. I still use the two original batterys 85 amp. hr.as used in rv. Not designed for traction, but giving very good results.

 

[blacktop]

thanks scotty, I use a rotary switch made by KRAUS & NAIMER.good quality cost 25 uk pounds. used on my 12--24 volt electric trike. 2 years hard use, still going strong.I use it like a gear box. I have studied the 4 qd option on their web-site, but its expensive. I dont abuse the batterys and using the switch is more interesting.

 

[OperaHouse]

Another option would be to use three single pole switches with each isolated by a diode to each battery tap. Each switch would select 12, 24 or 36V and the motor would always operate on the highest voltage. The diodes would prevent the voltage from frrding from one battery to another.