# Motorcycle conversion 12V system



## Matej (Dec 4, 2015)

P.S.
Are there any other forums that are popular primarily among electric motorcycle converters? I do like DIYEC very much, but I realize that it mainly caters to car conversions. The only other bigger forum I know of is Endless Sphere, but that one seems to focus mostly on E-bikes. Unless converting motorcycles is simply not as popular as cars or bicycles.
Thank you.


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## onegreenev (May 18, 2012)

If you are using a 12 volt battery to power the motorcycle and still need 12 volts for the electrical system then you should use a 12 volt battery. Most who use a DC DC converter use a battery pack for the motor that is higher than 12 volts. I used a DC DC on my first conversion after I switched to 96 volts. That DC DC never browned out and I always had a steady 13.5 volt supply even if the main pack was so low I could not use it for powering the vehicle. 

Are you using 12 volts for the motor?


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## onegreenev (May 18, 2012)

Id not use such a tiny battery. Find a good set of LiFePO4 cells and then put those in series for a good solid 12 volt battery. I used my DC DC to actually provide a solid 13.5 volts and to keep the 12v battery charged up. I used the 12v battery in the system as the DC DC was not up to the task of keeping the headlights on during night driving. It was plenty good for keeping the battery topped off and when I needed headlights for a heavier load it did just fine. If you use a battery within the system you will have to have a way to keep it charged. That is the reason people use DC DC converters because they don't want to install an alternator for the 12 volt power and for charging the battery. If you can find a good DC DC that will give you enough amperage output without damaging the unit then that would be a way to forgo the battery. But if your main system is 12 volts for the drive motor then all bets are off as I don't know of any DC DC converters that can provid you with 12 volts when your main pack is below 12 volts. That will cause a brownout and could cause you to have your controller shut down if the voltage goes too low.


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## MathisLaurant (Feb 21, 2017)

I know kelly has a few DC/DC converter maybe worth checking out what they have http://kellycontroller.com/dcdc-converter-c-33.html

might find something for your system


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## Matej (Dec 4, 2015)

onegreenev said:


> Are you using 12 volts for the motor?


Hello,
It will definitely be higher voltage.

My main question is; how do you close the main contractor if you only have a DC-DC converter without a dedicated 12V battery?

Sorry for not being clear.
The dilemma is that the contactor needs a 12V source to close, but since it is mounted before the DC-DC converter, the converter will not see any power from the battery pack until the contactor is closed. A Catch 22 situation.
So I assume that some sort of a switched bypass circuit is required to feed power from the battery pack to the DC-DC even before the main contactor is closed.

Thank you.


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## Johnny J (Nov 27, 2008)

I have used two different ways on my builds, I used DC/DCs in both. The first one I used is a main contactor that works on battery pack power (f.ex. 72V), something like this :http://kellycontroller.com/main-contactor-kzj-72vdc-coils-200amps-p-1150.html The disadvantage with this is that you have to run this voltage through the key switch and it's a little bit dangerous and can wear the switch out quite quickly if you don't use a way to soften the voltage rush.

On the other one I used a small 12V 1.3Ah lead-acid battery that is connected to the key switch and to a relay that closes the main battery pack voltage. The small battery is charged by the 13.5V DC/DC.


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## onegreenev (May 18, 2012)

I use a large circuit breaker before the main contactor. I switch on the breaker and that gives power to the system. Main controller is not on at this point but power is available at that point. I had a resistor on my main contactor for precharge too. Then I could at any time turn on the car. At the end of the day I'd shut off the circuit breaker to cut power to everything.


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## Spaceweasel (Mar 30, 2013)

Matej said:


> P.S.
> Are there any other forums that are popular primarily among electric motorcycle converters? I do like DIYEC very much, but I realize that it mainly caters to car conversions. The only other bigger forum I know of is Endless Sphere, but that one seems to focus mostly on E-bikes. Unless converting motorcycles is simply not as popular as cars or bicycles.
> Thank you.


You might check out emoto.net. I got a lot of friendly advice when building my motorcycle conversion.


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## StevO (Oct 18, 2017)

I highly recommend the Vicor dc-dc converter. Very small and reliable with high output. Here is a pic with one mounted to my controller mount that has a heat sink welded onto it:







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