Single 20S9P with 12v step down or 20S9P with 4S2P

[chronosgarage]

I’m building an electric motorcycle with qs 205 hub motor 72V 2000 W, Votol em100, and 20S9P battery.

My question is which one is better 20S9P battery with 12v step down, or 20S9P battery with separate 4S2P battery with 72v to 12v step down, charge controller and 16.8 to 12v step down to fulfill all the 12v need of the electric motorcycle?

Thank you for your help

 

[e-beach]

To me it is 6 one way 1/2 dozen the other. The exception being is the drain on your total range with a 12v step down off the battery. It won't be much but it would be something. If you went stand alone 12v the extra stuff you would need for charging ect, would be just more stuff to have to wire up and maintain.

I suppose what it really depends on is how much of a mileage drain the step down transformer system cost you in mileage depending on what you are powering.

My inclination is to go for a stand alone 12v system to separate the 12v systems in the event of a step-down transformer
failure.

 

[chronosgarage]

To me it is 6 one way 1/2 dozen the other. The exception being is the drain on your total range with a 12v step down off the battery. It won't be much but it would be something. If you went stand alone 12v the extra stuff you would need for charging ect, would be just more stuff to have to wire up and maintain.

I suppose what it really depends on is how much of a mileage drain the step down transformer system cost you in mileage depending on what you are powering.

My inclination is to go for a stand alone 12v system to separate the 12v systems in the event of a step-down transformer
failure.

Thank you for your reply. I think redundancy is on the safe side, like you mentioned. I’m powering led headlights low wattage, turn signal, brake lamp and horn. I think the 12v load is quite small. Do you think that it’s worth the hassle of a stand alone 12v?

 

[e-beach]

.......I think the 12v load is quite small. Do you think that it’s worth the hassle of a stand alone 12v?

Yes, solely because an open short through a step down transformer could blow out your 12v system, fuse dependent. Of if the transformer fails, like on a hot day, you could find yourself riding in the dark. Stranger things have happened.

I think I would prefer the redundancy of two separate systems to keep them each simple. As it is I run my headlight and running flashers off their own batteries for the reason of simplicity. When something goes wrong with your electrical system, it is one less thing to worry about.

 

[chronosgarage]

Thank you for your reply. I think i will go in that route.

 

[Cdub]

I see 3 possible solutions.

Wiring up a step down converter would be simpler but you will of course have efficiency losses.

Having a standalone 12v pack with need capacity to match your ebikes running range seems more efficient solution but requires charging both batteries when needed. Also adds extra weight and uses more space.

If you have a small 12 V (buffer) battery that can be charged from your main battery. You can carry a smaller 12v battery which is good for weight and most people ride during the day. Only at night would you see range depletion due to charging/running lights. There is small efficiency loss from charging as well.

IMO a fuse is a good safety measure for the 12v to lighting even though I don’t use any between my battery and controllers.


Sent from my iPhone using Tapatalk

 

[thepronghorn]

How do you turn on your bike? Sometimes a standalone 12V battery is needed to power the coil on the contactor of the main battery. This is standard for large electric vehicles that are running 300V+ main battery packs. For a 20S battery, you may be electing to forgo a contactor in which case you could probably get away without a 12V battery.

 

[chronosgarage]

I see 3 possible solutions.

Wiring up a step down converter would be simpler but you will of course have efficiency losses.

Having a standalone 12v pack with need capacity to match your ebikes running range seems more efficient solution but requires charging both batteries when needed. Also adds extra weight and uses more space.

If you have a small 12 V (buffer) battery that can be charged from your main battery. You can carry a smaller 12v battery which is good for weight and most people ride during the day. Only at night would you see range depletion due to charging/running lights. There is small efficiency loss from charging as well.

IMO a fuse is a good safety measure for the 12v to lighting even though I don’t use any between my battery and controllers.


Sent from my iPhone using Tapatalk

Thank you for your reply. That’s great information.

 

[chronosgarage]

How do you turn on your bike? Sometimes a standalone 12V battery is needed to power the coil on the contactor of the main battery. This is standard for large electric vehicles that are running 300V+ main battery packs. For a 20S battery, you may be electing to forgo a contactor in which case you could probably get away without a 12V battery.

The system I’m using now is the elock cable (battery voltage) from the 72v alarm to trigger a 72v relay that connects the 72v battery to 72v to 12v step down converter. Once the 12v is available, key switch at acc position will trigger a 12v contactor that will connect the battery to the controller. At the on position it will trigger a 12v relay that will connect the main battery positive to the elock pin on the controller to turn the votol em100 on.

The other option is to use 4S2P battery connected the 72v relay that will be triggered by elock alarm to power the 12v system. The 20S9P battery is also connected to a step down converter that will bring down the voltage to 16.6V and connected to charge controller that will trigger when the 4S2P battery reach 12V and will shut off once it reach 16.5V.

What do you think about this setup?

 

[thepronghorn]

How do you turn on your bike? Sometimes a standalone 12V battery is needed to power the coil on the contactor of the main battery. This is standard for large electric vehicles that are running 300V+ main battery packs. For a 20S battery, you may be electing to forgo a contactor in which case you could probably get away without a 12V battery.

The system I’m using now is the elock cable (battery voltage) from the 72v alarm to trigger a 72v relay that connects the 72v battery to 72v to 12v step down converter. Once the 12v is available, key switch at acc position will trigger a 12v contactor that will connect the battery to the controller. At the on position it will trigger a 12v relay that will connect the main battery positive to the elock pin on the controller to turn the votol em100 on.

The other option is to use 4S2P battery connected the 72v relay that will be triggered by elock alarm to power the 12v system. The 20S9P battery is also connected to a step down converter that will bring down the voltage to 16.6V and connected to charge controller that will trigger when the 4S2P battery reach 12V and will shut off once it reach 16.5V.

What do you think about this setup?

The first system sounds fine. The second one might be a bit safer since you aren't manually switching 72V. Instead of cycling the 12V battery with your charge controller, what about getting a 12V converter with a current limit and setting the voltage to somewhere around the nominal voltage of the 12V pack. Should save you some cycles on the 12V pack.

 

[chronosgarage]

How do you turn on your bike? Sometimes a standalone 12V battery is needed to power the coil on the contactor of the main battery. This is standard for large electric vehicles that are running 300V+ main battery packs. For a 20S battery, you may be electing to forgo a contactor in which case you could probably get away without a 12V battery.

The system I’m using now is the elock cable (battery voltage) from the 72v alarm to trigger a 72v relay that connects the 72v battery to 72v to 12v step down converter. Once the 12v is available, key switch at acc position will trigger a 12v contactor that will connect the battery to the controller. At the on position it will trigger a 12v relay that will connect the main battery positive to the elock pin on the controller to turn the votol em100 on.

The other option is to use 4S2P battery connected the 72v relay that will be triggered by elock alarm to power the 12v system. The 20S9P battery is also connected to a step down converter that will bring down the voltage to 16.6V and connected to charge controller that will trigger when the 4S2P battery reach 12V and will shut off once it reach 16.5V.

What do you think about this setup?

The first system sounds fine. The second one might be a bit safer since you aren't manually switching 72V. Instead of cycling the 12V battery with your charge controller, what about getting a 12V converter with a current limit and setting the voltage to somewhere around the nominal voltage of the 12V pack. Should save you some cycles on the 12V pack.

That’s a great idea. Thank you