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Discussion Starter · #1 ·
Thank you in advance..

I'm new to this forum and wiring up a constant speed, 48v DC motor for a lawn tractor conversion.

This motor is designed for this application and does not use a controller. It runs at 3600RPM constant and tractor speed is controlled by tractor's transmission.

Can some one look at the attached wiring diagram to be sure I'm on the right track.

The contactor is 400a / 48v

I have 400a fuses and holders. Do I need to fuse each battery? Or will one fuse at the last 12V battery feed suffice.

I'm using 2/0 copper welding cable with the longest run of 36"


Thank you for all your help.
 

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Was there any information about using freewheeling diodes on the contactor coils, or any snubber across the main contacts? also for the "switch" device shown connected to "ground"? Without something like this the life of the contactor will be shortened.

Is the chassis connected to the "ground" i.e. the (-) terminal of the lowest 12V battery going to the Motor (-)? That would be a good practice, but i wouldn't recommend to rely on the chassis to carry any return currents, use a wire with a fuse to provide a known good path.

Generally you need a fuse in a circuit to prevent wires from burning in case of a shorting event. If the chassis is grounded, then any wire that could rub against the chassis might short.

The size of the fuse is determined by the size of the wire that must be protected. For all of the 2/0 gage wire then the 400A fuse might be okay, but for the little wire that engages the contactor coils, that is too big.
 

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Discussion Starter · #3 ·
Thank you...

Yes, I have the diode for the contactor. Sorry I didn't include it in the drawing.

The contactor gets its 48v from the mail battery in.....all it needs is a switched ground to activate.

So it appears all the battery interconnecting wires should be fused?
 

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no just one fuse per circuit--the main battery links are all in the same circuit, but the "switch" is a different circuit.

Does the switch have a snubber or free wheeling diode too? You will need transient protection for both the contacts and the coil of the contactor 9for when you want to interrupt the current to turn them OFF)

Please redraw your schematic with the correct fuse and diode features.

You didn't answer about the grounding question.
 

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What kind of motor are you using, do you have a model or part number?

i couldn't find a real spec sheet for your contactor, but someplace indicated that the contacts were "silver oxide"--not sure if that is tarnished silver or some alloy?

but you do need the diode as shown, and a snubber (Resistor-Capacitor in series) across the main contacts (at least if you want it to last more than a few cycles of ON/OFF operation).

One big fuse to protect all the fat wires, and one small fuse to protect the wiring for the switch from the coil.
 

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Discussion Starter · #7 ·
Motenergy ME1004 Brush-Type Permanent Magnet DC Motor

This is the motor I'm using....
 

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Discussion Starter · #8 ·
and a snubber (Resistor-Capacitor in series) across the main contacts
I'm surprised that the manufacturer of the motor never mentioned this when I spoke to them. Could it be built into the contactor.

If not, any idea of the value I'd need?
 

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Maybe they will give you some recommendations on the snubber values, if not we can calculatus some that will work for that thang.

Is this the sort of wiring scheme that you came up with after some research?
i'm using a single point ground at the pack low side, run wires for anything that needs to carry current, don't rely on chassis to be your current carrier except in off-nominal situations.
 

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Discussion Starter · #11 ·
Thank you very much...This is very helpful....I know enough about DC electricity to be dangerous. Learning more every day.....

So I looked at the little envelope that came with the contactor. It included the resistor....But no diode. I ordered the diode on their web page.

The vendor that sold me the motor and contactor does not list capacitors on their web page. I emailed them to see what they suggest for values. Haven't heard back yet.

One fellow on another forum suggested I don't need a capacitor for a DC motor???? I have no idea if this is accurate.
 

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Discussion Starter · #12 ·
BTW...You show the 400A fuse on the negative leg.....Does it matter if it is on - or + ?
 

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...

The vendor that sold me the motor and contactor does not list capacitors on their web page. I emailed them to see what they suggest for values. Haven't heard back yet.

One fellow on another forum suggested I don't need a capacitor for a DC motor???? I have no idea if this is accurate.
Most folks with golf carts use the contactor to provide main power to their Motor Controller. They need the bypass resisitor to pre-charge the capacitors found within the motor controller box, then they use a throttle device to control the speed. They don't use snubbers across the contacts.

You said you don't need any speed control and are going to run it wide open with no controller. That is a very different situation than everyone else, and it requires a different solution. You don't need the precharge resistor, but you will want a snubber circuit to prevent damage to the precious metal contacts in the contactor when you switch it off. The snubber provides a conduction path for inductive spikes to dissipate in a similar manner that the diode does for the control coil. You could replace the snubber with a big ass diode also, but it would likely be a more expensive solution.

The fellow on the other forum hasn't really thought thru his suggestion; what do you think would happen if you wired it up with a resistor but no capacitor? What is the purpose of the resistor without a motor controller?
 

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Discussion Starter · #15 ·
what do you think would happen if you wired it up with a resistor but no capacitor? What is the purpose of the resistor without a motor controller?

I have no idea...But before I wire this thing up I'm going to call and talk to a technician at the vendor
 

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Answer: If you put the bypass resistor, without a capacitor, then the motor will be energized thru the resistor all the time. It will be trying to run and bleed your battery down.

If you wire up the contactor without a snubber, then there will be arcing and sparking across the precious metal contacts whenever you turn off the motor. This will eventually pit, erode and frost over the surfaces such that it will no longer function.

To see this you could use some car jumper cables to connect and run your motor directly from the pack, then notice the sparking when you make and break the connection, and the black residue on the tip of the clamp.
 

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Discussion Starter · #17 ·
Thank You for your help...Waiting to hear back from the vendor on the capacitor.

Does the capacitor stop the bleed down of the battery?

If power is removed via the Deadman switch before the contactor, then I imagine I'll have no bleed down issues....??
 
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