Hi i was wondering if there is a safe way that i can drop voltage ?
I want to drop the voltage of a lipo battery pack 7.4V to about 6.2 V by adding somthing befoere the power gets into the esc.....is there a safe way of doing this?

Running voltage through a diode will drop it by 1.5 volts. The current load will determine what size of diode you need.

Would i have to run the diod backwards?
positive ------|=------

Nope. Diodes only allow current one way. You wire it up backwards and you effectively have an off switch in the circuit. It doesn't hurt anything though so this is a safe mistake to make.


Hmmmmm I wonder if this would make a cheap circuit breaker to protect a board. I think if you run too much current through the diode it burns up and fails, shutting power to the circuit. Perhaps this is a way of protecting heng long boards when the motors stall out????? Anybody know if this would work???.

Actually, a [link=http://en.wikipedia.org/wiki/Resistor]resistor[/link] is what you will need to drop voltage. We used them in controllers when we raced HO cars back in the day. You used to be able to buy cheap ones at Radio Shack, but make sure the wattage is correct for the use your operating with.


Jeff

Diodes drop voltage by 1.5 volts, and if that is about what you are looking for they present themselves easy for this task. Agreed resister are designed to drop voltage, but then you have to dust off ohms law to calculate what you need.

would a led diode drop voltage 1.5?

Yes i thought the diode would work.
You don't whant to use a resistor because they burn off to much energy a diod runs cooler and will drop voltage without draining the battery like a resistor.

Keep in mind that a diode doesn't drop voltage by a perfectly consistent 0.7v. It drops voltage in proportion to the current flow. So, at low current flow, it may only drop a few hundred millivolts, at "high" current flow, you'll get your desired 0.7v drop.

YHR, Dunno how consistent a diode fails. A fuse would probably be more reliable.

D.

Edit: Diodes drop 0.7v, not 1.5v

Hi i have some diods and they only drop voltage about .5v
(Example)

say i have a charged battery that reads 6Volts with my meter i then add one diod and the final reading will be about 5.5V on the battery?
I don't see how 1.5V should be reduced from adding a diod ....I think it's more like .5Volts?

See Darkith's post. As current draw is increased they will reach their 1.5 voltage drop. When you buy a diode it will tell you on the packaging the voltage drop across it.

If you are going to use a diode you will need a schottky diode. Depending on the current you are passing you may want to consider a voltage regulator but that will bring it down to 5V which may be too low.
Remember that LED resistors are rated for very low throughput, usually 1/8 watt. A HL can pull 35 watts so you would need a big one.

Dusting off ohm's law V=IR voltage drop=current x resistance
Also; P=IxIxR power rating of resistor=current x current x resistance

Don't insert taps between the cells of a LIPO battery. It's dangerous.

How about an inline fuse?? I think we are on the right track here. What about something that senses heat and shuts things down?? I'm not an electronics guy but maybe somebody else has some know how on this. Could save us alot of trouble with replacing boards.

If you are looking for protection as opposed to lowering the voltage there are many ways to do it.
I would recommend an overcurrent thermal protector like the ones here
http://www.trankey.com.tw/cgi-bin/pr....pl?ProdID=110

The advantage of these over fuses is that they reset themselves when they cool down so you won't have to replace fuses.

so pscartozzi if i wnated to drop a 7.2 hl pack down to 6 volts exactly what doide could i use? got a link or anything?

As far as a diode recommendation I stand corrected, You want to use a Zener, not a Schottky. You need one rated at 6V and probably 5 watts. I could not find one on a quick search but this isn't my speciality.

Here's a link to a page that describes the process;
http://www.reuk.co.uk/What-is-a-Zener-Diode.htm

You may want to consider an off the shelf regulator
http://www.lynxmotion.com/Product.as...&CategoryID=48

Guys:

A zener is what we used way back before they made BEC receivers. I used to race offroad electric and ditching the 4x AA battery helped lots. It was iffy if you ran a hot modified though, because your Rx tended to cut out if the car pack got too low... then again, car couldn't go too nuts too fast... and adding a failsafe board solved that issue.

Then Tamiya began making that add-on board that had one to go with their MSC's, and soon Futaba and others were integrating it into the Rx's.

If its your ESC that you are worrying about, why not power it from the Rx supply? If the Rx has BEC, it can regulate for the ESC, right?

Hi I just want to run something after my battery to make the voltage drop like 1 volt or so before the voltage reaches ESC

Put a few diodes (high current diodes) in series until you get the drop you need. Otherwise you can use a regulator, but you will need one that is adjustable and can handle the power you need (how much current will you draw).

The regulator will keep the supply voltage steady with varying amount of current draw, you will need a low dropout regulator as most require a 2 volt minimum from the input voltage to the regulated output. Here you are talking about 1.2 volts which is low (a couple diodes may be your best bet).

Remember a charged pack will measure more that 7.4 volts.

If this is for dropping the voltage of a Lipo pack to power a tank, I don't think a Zener diode is a very good choice, as Zener's are really only good for providing power to low current circuits, or where current's remain relatively stable. A Zener will also waste power even when low current is flowing.

Shenlonco, a little more detail might help. But, if you're just trying to drop some voltage to keep the tank's speed the same, using high-wattage diodes inline might be cheapiest/easiest. At really low currents, the voltage will be higher, but once the motors kick in, the current should force the diode into the range at which the drop is closer to linear. Hopefully whatever electronics you're using won't care about the higher voltage when the motors are off.

D.

I tried the diods 3 amp ones they worked!

from my experience with tam tanks, I do not need to but a resistor or diode to run lipos, not sure if the board of those HL s are that sensitive to voltage increases, also take note that lipos should not be disc harged below 2.5v per cell as this will damage the cells. Best find out what is teh low voltage cut off for teh tank too. Good luck with your lipo conversion then

Good point Planedev, though the cutoff should be at no less than 2.7v under load or 3.0v resting voltage.
For newer batteries which are capable of sustaining their output voltage even when discharged close to capacity, Lipo manufacturers are even starting to recommend a cutoff of 3.0v under load or 3.3v resting voltage.

D.

If you need more than 3 amps, a packaged rectifier could be used and can have ratings up to 30 amps.

What ESC's are you running? The ESC's may be able to withstand a voltage range to include your setting.

Hi it's 2 micro esc's that only ran on 5 cells Max
But i got it figured out now so thanks for all the GREAT help guy's
HAPPY TANKING!