Converting 48v DC to 36v DC?

alfantastic

10 kW
Joined
Mar 29, 2011
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UK
Is there any reliable way, without spending mega bucks, to convert 48v DC to 36v DC, whilst maintaining a current output of at least 15 amps?

I've seen buck converters for just about every voltage other than 36v :cry:
 
I've seen adjustable buck converters from china. The ones below all seem to be rated for 15A, which means it can really do about half that continuously. It may be possible to use two of them in parallel. The price is cheap enough..

http://www.ebay.com/itm/DC-12V-48V-to-DC-5V-24v-15A-Adjustable-Buck-Module-Step-Down-Voltage-Regulator-/361439141933?hash=item542773a02d:g:vLMAAOSw8-tWWs6F

http://www.ebay.com/itm/200W-15A-DC-DC-8-60V-48V-TO-1-36V-5V-12V-24V-19V-Buck-Converter-Step-down-power-/221926994738?hash=item33abe13332:g:Z4AAAOSwq19XBs0G

http://www.ebay.com/itm/200W-15A-DC-DC-8-60V-TO-1-36V-12V-Voltage-Power-Buck-Converter-Step-down-P6H3-/122492995900?hash=item1c8526c93c:g:wEEAAOSwlY1ZFeb4
 
If they're only rated for 200w you might need at least three of them, depending on how exaggerated that wattage rating is, and how much current you're actually pulling thru them.

Some of these things might also need fan cooling above a certain wattage output, so keep that in mind.


If you're wanting to use a 48v battery with a 36v ebike, it'd be an interesting experiment to try. Keep in mind it will decrease your range by whatever percentage inefficiency the converters have.
 
Don't think those converters would last very long on an electric bike. Anyone else got any ideas on how to accomplish this?
 
Ideas? Yes. Tested? No....

Won't be small, but you could use a brushed motor controller rated for more than the current you need (you don't want it to start limiting current at all cuz it'll drop the voltage to do so), with a large capacitor bank on it's output instead of a motor, to smooth the PWM output into a flat DC voltage. Might also need a series inductor between controller and capacitor bank.

Use a mounted on the controller for a throttle control, and set it so that the final PWM voltage is whatever you need your system voltage to be. Probably around 3/4 of full throttle, for converting 48 to 36. Then lock it off. Or use a pot to determine resistance needed, and then use a plain resistor. (or resistive voltage divider).

Some controllers have a "throttle high lockout" so if throttle is not at zero when they power on, they won't do anything. If you get a controller that does that, you'll have to have a switch between the system and this contraption, and use a throttle pot (or a switch between the voltage divider output and the throttle input), and set it to zero before turning it on, and then power up, then set it to the right output voltage (or flip the switch on), before switching on the connection between this and your system to turn on the bike.


Like the DC-DC's, this would also reduce your range by the efficiency of the conversion.

Personally, I think it would be easier to replace the actual controller on the bike to one that takes 48v. :)
 
What are you trying to accomplish? If you're unconcerned with efficiency, and only want to drop voltage, you can get a handful of power diodes for a few bucks that will burn off about 2V each. Give them enough heat sinking and you can pick however much reliable voltage drop you want.
 
amberwolf said:
Ideas? Yes. Tested? No....

Won't be small, but you could use a brushed motor controller rated for more than the current you need (you don't want it to start limiting current at all cuz it'll drop the voltage to do so), with a large capacitor bank on it's output instead of a motor, to smooth the PWM output into a flat DC voltage. Might also need a series inductor between controller and capacitor bank.

Use a mounted on the controller for a throttle control, and set it so that the final PWM voltage is whatever you need your system voltage to be. Probably around 3/4 of full throttle, for converting 48 to 36. Then lock it off. Or use a pot to determine resistance needed, and then use a plain resistor. (or resistive voltage divider).

Some controllers have a "throttle high lockout" so if throttle is not at zero when they power on, they won't do anything. If you get a controller that does that, you'll have to have a switch between the system and this contraption, and use a throttle pot (or a switch between the voltage divider output and the throttle input), and set it to zero before turning it on, and then power up, then set it to the right output voltage (or flip the switch on), before switching on the connection between this and your system to turn on the bike.


Like the DC-DC's, this would also reduce your range by the efficiency of the conversion.

Personally, I think it would be easier to replace the actual controller on the bike to one that takes 48v. :)
Thank you amberwolf, but you totally mind-fuzzled me after the first sentence :shock:
 
Chalo said:
What are you trying to accomplish? If you're unconcerned with efficiency, and only want to drop voltage, you can get a handful of power diodes for a few bucks that will burn off about 2V each. Give them enough heat sinking and you can pick however much reliable voltage drop you want.
I want to fit a totally UK EAPC legal kit to a bike, using a spare 48v battery I have. The battery has decent cells, so don't want to waste its usefulness.

There are UK legal kits aplenty for 36v, but they all seem to go power crazy on the 48v kits.

These are the current rules:

EAPC requirements

The requirements are:

the bike must have pedals that can be used to propel it
the electric motor shouldn’t be able to propel the bike when it’s travelling more than 15.5mph
the motor shouldn’t have a maximum power output of more than 250 watts

It must also display one item from each of the following:

the power output or manufacturer of the motor
the battery’s voltage or maximum speed of the bike

So I do need to have a 250w motor fitted and the bike limited to 15.5mph.
 
Have you considered taking your 48v battery apart and using something like the Vruzend DIY 18650 kit and reconfiguring the cells to 36v.

Sent from my D101 using Tapatalk
 
alfantastic said:
There are UK legal kits aplenty for 36v, but they all seem to go power crazy on the 48v kits.
You could open up the 48v controller and cut one of the shunts (assuming there are two) to cut it's current limit in half.

If you need to cut the current down further, you can begin shaving off metal from the other shunt.
 
I think the simple way to do this is to (a) have the motor with a valid 250W label and (b) a controller that can run 36V/48V with a speed limiter set via your LCD. This eliminates all the efficiencies and costs that crop up with voltage conversion.

If you find a controller with a 250W label, well that's great, but I would think you would be legal with a 350W model, as long as you have limited the speed. I can't tell you if any of the controllers on my ebikes have the wattage on the label. I have one junker on my desk and it has no watt rating, just the voltage and max current.

Small controllers aren't that expensive either.
 
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