Brushed controller as dc-dc converter?

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veloman   1 GW

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Brushed controller as dc-dc converter?

Post by veloman » Aug 16 2015 11:54pm

So I got this wild idea. I want to keep a 12v lead battery charged, using my 60v ebike battery. With a 60v brush controller and throttle I would installl a blocking diode so only current could flow to the 12v battery. Then set throttle position so the controller outputs 14v. The controller is current limited.

Any reason this would not work? Stopping periodically to keep the controller from over heating is not a problem.

Though you could likely reduce current by gradually reducing throttle too.

Why not just get a dc converter? The cheap ones don't allow fine tuning the output voltage from what I've seen. And brush controllers are cheap.
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Russell   10 MW

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Re: Brushed controller as dc-dc converter?

Post by Russell » Aug 17 2015 12:05am

veloman wrote:
Why not just get a dc converter? The cheap ones don't allow fine tuning the output voltage from what I've seen. And brush controllers are cheap.

I don't know about using a brushed controller but two winters ago I used my E-bike battery with a DC-DC converter to keep my car battery charged during an extreme cold snap while I was at work. It worked quite well and was easily fine-tuned. This is the model I used;

https://endless-sphere.com/forums/viewt ... 31&t=21459

-R
Jeep Comanche Trekking Bike w/YOUE geared motor, 42 lbs + 15 lb rear trunk bag w/12S 16Ah LiPo battery, tools, etc., 21A controller, 700 x 40C tires. 27 MPH.


My other E-Bikes: Nashbar Steel Flatbar

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Re: Brushed controller as dc-dc converter?

Post by amberwolf » Aug 17 2015 12:20am

veloman wrote:Any reason this would not work? Stopping periodically to keep the controller from over heating is not a problem.
You'll just need to add the appropriate sized inductor and capacitor, if you don't want the current/voltage spikes from the PWM output of the controller on your battery.


I suppose the question is: why do you need to keep that 12v battery charged, and why do you need to use your ebike pack for that?

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veloman   1 GW

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Re: Brushed controller as dc-dc converter?

Post by veloman » Aug 17 2015 12:59pm

It's to improve mpg on my car. Reduce alternator load by keeping the battery full. Current spikes are not an issue at 20amps.

The ebike battery is worthless so I am trying to find a use for it. Or for when I take my ebike on a road trip.
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Russell   10 MW

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Re: Brushed controller as dc-dc converter?

Post by Russell » Aug 17 2015 1:58pm

veloman wrote:It's to improve mpg on my car. Reduce alternator load by keeping the battery full. Current spikes are not an issue at 20amps.

The ebike battery is worthless so I am trying to find a use for it. Or for when I take my ebike on a road trip.
Even if the battery is fully charged the alternator does still have to supply power for the ignition system, lights, climate control, entertainment system, etc., or you want the 60V battery to help power those too?

If your car battery is discharging more than normal because you don't use your vehicle often or don't drive it far then using the 60V battery to keep it topped off isn't a bad idea. Like I mentioned above though a DC-DC converter set for a trickle charge would get the job done nicely. I used an "always on" power port to feed the current back to the battery. However if you park where you have access to ac power then an automatic battery maintainer might be a better solution.


-R
Jeep Comanche Trekking Bike w/YOUE geared motor, 42 lbs + 15 lb rear trunk bag w/12S 16Ah LiPo battery, tools, etc., 21A controller, 700 x 40C tires. 27 MPH.


My other E-Bikes: Nashbar Steel Flatbar

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veloman   1 GW

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Re: Brushed controller as dc-dc converter?

Post by veloman » Aug 17 2015 2:07pm

Yes i want my 60v battery to essentially power all the electronics in the car.

I am assuming that when driving, the 12v battery voltage sits around 13v. Some ecomodders remove their alternator and install a large marine/rv 12v battery. So I thought that if I instead just keep the car's 12v battery at 14v, then the alternator would not be running. But maybe I'm wrong?

A typical alternator is very inefficient at 50-60%. So if the car needs 300watts of electrical power, that actually requires perhaps 550watts of engine power. For a very efficient small car at lower speeds, that can easily be 10% of the total vehicle's power requirement.
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Re: Brushed controller as dc-dc converter?

Post by dnmun » Aug 17 2015 2:24pm

you should avoid doing stuff that can damage all of the electronic devices connected to the wiring of your car in hopes of saving a penny. jmho.

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r3volved   100 kW

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Re: Brushed controller as dc-dc converter?

Post by r3volved » Aug 17 2015 3:13pm

dnmun wrote:you should avoid doing stuff that can damage all of the electronic devices connected to the wiring of your car in hopes of saving a penny. jmho.
Or mod your wife's car first :D
(ya, i'm single...)

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Russell   10 MW

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Re: Brushed controller as dc-dc converter?

Post by Russell » Aug 17 2015 3:30pm

I don't recommend doing this. In theory if you supply the electrical loads of the car with the E-bike battery the alternator load on the engine would be minimal. If the 60V battery output is regulated at around 14V then the alternator should not have much to do and won't load the engine...but what a hassle! I mean I used my lithium battery to trickle charge a (9 yr old) car battery for a few days during a cold snap but I sure wouldn't want to do it on an permanent basis.

Maybe think of another project for that old E-Bike battery. Got any car radios/speakers lying around...build a portable boom box. Or how about a portable power station with converter and inverter for 5/12VDC and 120vac outputs. Put a small compressor in it for filling tires and some powerful lights. Here in Wisconsin I would consider reconfiguring it for 12V and make a jump starter for winter emergencies.

...or just give away/junk/re-cycle it and forget the whole thing :P

-R
Jeep Comanche Trekking Bike w/YOUE geared motor, 42 lbs + 15 lb rear trunk bag w/12S 16Ah LiPo battery, tools, etc., 21A controller, 700 x 40C tires. 27 MPH.


My other E-Bikes: Nashbar Steel Flatbar

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Gregory   100 kW

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Re: Brushed controller as dc-dc converter?

Post by Gregory » Aug 17 2015 4:05pm

dnmun wrote:you should avoid doing stuff that can damage all of the electronic devices connected to the wiring of your car in hopes of saving a penny. jmho.
haha, says the man who drives with this pile of recycling in his backseat (which I am totally jealous of) :wink:

Image


1) x5305 Hub Motor in a 24" Sun rim with 10G spokes, Kelly 72601 controller, 74V 10Ah Turnigy LiPo 20C Battery and CycleAnalyst
2) Mac 10T rear hub in a 700C "comfort bike" 15S 5Ah LiPo, stock 28A Xie Cheng controller
3) 38" Longboard, Turnigy 6374, CC Mamba XL2 ESC

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veloman   1 GW

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Re: Brushed controller as dc-dc converter?

Post by veloman » Aug 17 2015 5:02pm

I"m probably not going to do this. I just was curious if it was possible.

I am likely going to be getting a car again, for use when the ebike doesn't make much sense. The car may be a gen1 Insight or another older hybrid that I will ecomod for max mpg. I've lost interest in riding my converted emotorcycle, it just feels too dangerous with so many idiot drivers. I was reading the Vetter Fuel Challenge results and a few years ago, a gen1 Insight was right up there in mpg with the streamlined motorcycles. To me, a hyper efficient car is more appealing than a motorcycle if they are not that different in power consumption.
But I want to explore all avenues for getting the highest mpg utilizing parts I already own. Hence - this thread.
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dnmun   100 GW

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Re: Brushed controller as dc-dc converter?

Post by dnmun » Aug 17 2015 9:37pm

if the mosfets on the output shorted it would deliver the full voltage to the wiring.

if your adjustment of the throttle input shifted by accident it could push the voltage well above what you initially set it to.

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