DC to DC step up converter

[Alastor]

Hello again ,

I have two 36v10ah packs that are sitting at my house and i was thinking if there is a DC to DC step up converter that i can use so i can achieve 48v volt 7-10amp output for my scooter.

The scooter has 3 speeds.At 1st speed it consumes 330 watts and the batteries can handle up to 360 watt before the BMS shut down.
So i was thinking of a DC to DC step up converter with :

Input voltage :29 - 44 VDC
and
Output : 48VDC 7-10 Amp

Anyone ever done something like that ? I cant find anything can help me with finding one ?

 

[magudaman]

No one does this because it is usually quite wasteful. The DC-DC converters are usually only around 85% efficient which equates to around 50-80w of loss. There are some cheap ones that just started hitting ebay not long ago and may perfect:

http://www.ebay.com/itm/DC-DC-600W-10-60V-to-12-80V-Boost-Converter-Step-up-Module-Power-Supply-/170893208817?pt=LH_DefaultDomain_0&hash=item27ca076cf1

If that doesn't come up just search ebay for 600w dc-dc and they will come up. For your voltage it looks you could have somewhere around 500 watts on the output. Heck there only $23 bucks!

The DC-DC converter may also may not be super happy about the motor controller pulsing when controlling motor speed.

 

[Bazaki]

For the 23 bucks you can play around with it but it is not a good solution, from about 8A input the converter gets hot, 8A x 37V = 296 Watt at 85% efficienty is about 250 Watt at the controller.

 

[Alastor]

No one does this because it is usually quite wasteful. The DC-DC converters are usually only around 85% efficient which equates to around 50-80w of loss. There are some cheap ones that just started hitting ebay not long ago and may perfect:

If that doesn't come up just search ebay for 600w dc-dc and they will come up. For your voltage it looks you could have somewhere around 500 watts on the output. Heck there only $23 bucks!

The DC-DC converter may also may not be super happy about the motor controller pulsing when controlling motor speed.

Thanks a lot for the suggestion i know of the losses but in my case the load is quite small so i think i can experiment with it with little cost.
I know i will have to stick to the lowest speed but i am tempted to check it out i may carry the pack with me in case of need you never know when you might need it and its so light weighted.

 

[Alastor]

For the 23 bucks you can play around with it but it is not a good solution, from about 8A input the converter gets hot, 8A x 37V = 296 Watt at 85% efficienty is about 250 Watt at the controller.

Yea probably you are right but still i wanted a step up little converter anyhow so for 30 dollars at my door its not a bad deal after all The controller i had was pulling 360 watt at full speed and the battery's bms never complained.I did some math and i found out that it might be possible 48v*7a =336 watt at 1st speed + efficiency losses 85% 386 watt.The only thing it concerns me its that when the voltage diference is great for example input 34 and require to get 48 v i dont know if the converter will be stable.

 

[Bazaki]

I'm curious how exactly this will turn out, maybe it will work good enough to you, please share the results

 

[Alastor]

I'm curious how exactly this will turn out, maybe it will work good enough to you, please share the results

Ofc i will share the results.I am just looking for this kind of step-up converter in the European market because if i order it from the USA it will take an age to get it.

 

[Alan B]

It would be much more efficient to use a boost rather than a full converter. Then the efficiency loss is applied only to the boosted portion of the power. The converter generates 12 volts and adds it to the battery voltage to get the 48. So it is a 36:12 volt down conversion, isolated, with the output in series with the battery, across a diode. So when the converter is off you get 36 volts minus the diode drop, and when the converter is powered it adds 12 volts and you get 48 V and the diode is back biased so it does nothing. Put a big switch or relay on the booster and label it "Turbo Boost".

Also note that the power will likely double at 48V from what it was at 36V, or nearly so. Both the voltage and current go up.

 

[hjns]

If your controller can handle 74V, you are much better off putting your packs in series and be done with it. It would even make it attractive to buy a 74V controller if you haven't got one.

 

[Alastor]

It would be much more efficient to use a boost rather than a full converter. Then the efficiency loss is applied only to the boosted portion of the power. The converter generates 12 volts and adds it to the battery voltage to get the 48. So it is a 36:12 volt down conversion, isolated, with the output in series with the battery, across a diode. So when the converter is off you get 36 volts minus the diode drop, and when the converter is powered it adds 12 volts and you get 48 V and the diode is back biased so it does nothing. Put a big switch or relay on the booster and label it "Turbo Boost".

Also note that the power will likely double at 48V from what it was at 36V, or nearly so. Both the voltage and current go up.

I saw this boost converters last night they tend to have 95% efficiency and that's a good thing.Very nice idea mate thanks a lot.
I was thinking connecting the two packs in series via diodes on the BMS output and get a new 1000 watt controller that my motor can handle and push the scooter in 72Volts but this toy is not made for speeds like that so i am trying only to use the extra packs i am having.

So if i got you right you are saying having one pack at 36 volts and having the output of the booster in series with the 36 volt pack to get the plus 12 volt to get the 48 plus voltage.And use a good anti shock diode rated at 15 A and 80 volts.Did i got this right ?

Thanks again

 

[Alastor]

If your controller can handle 74V, you are much better off putting your packs in series and be done with it. It would even make it attractive to buy a 74V controller if you haven't got one.

If you see my scooter you will understand why i don't want to go to 72v system http://endless-sphere.com/forums/viewtopic.php?f=7&t=40048 .Its just a toy really.

 

[Punx0r]

You don't have to use the full speed of 72V You could limit motor speed in the controller software, or limit the throttle.

 

[Alastor]

You don't have to use the full speed of 72V You could limit motor speed in the controller software, or limit the throttle.

Hmmmm nice idea but i think we all tend to run more if we have the power I want to make my Saracen hardtail 72V one day that can handle more speed and has hydraulic disk breaks

 

[hjns]

You don't have to use the full speed of 72V You could limit motor speed in the controller software, or limit the throttle.

Hmmmm nice idea but i think we all tend to run more if we have the power I want to make my Saracen hardtail 72V one day that can handle more speed and has hydraulic disk breaks

Well, then you are just in the way of yourself. I would say, just program the controller for a max speed of 66% and you are done. I do it all the time. Nothing wrong with 72V, and it makes everything much simpler and more efficient.

 

[Alastor]

You don't have to use the full speed of 72V You could limit motor speed in the controller software, or limit the throttle.

Hmmmm nice idea but i think we all tend to run more if we have the power I want to make my Saracen hardtail 72V one day that can handle more speed and has hydraulic disk breaks

Well, then you are just in the way of yourself. I would say, just program the controller for a max speed of 66% and you are done. I do it all the time. Nothing wrong with 72V, and it makes everything much simpler and more efficient.

In time i will eventually get a nice 72 Volt controller.I just can't find more details about my motor in order to determine how many amps it can handle maximum so i don't burn it .
All i know is that the controller i have can provide 17a at 48v so about 800 watt of power.

 

[Alan B]

Specs probably won't help you much. A temperature probe and some experiments will tell you more.

 

[Alastor]

Specs probably won't help you much. A temperature probe and some experiments will tell you more.

Nice to know i have everything except the controller