Voltage Regulator (need a quick question answered) - RC-Monster Forums

BP-Revo · **Voltage Regulator (need a quick question answered) -** 11.12.2007, 09:08 PM

Ok, I have a Hitec CRX Transmitter. It currently uses a 8 cell AA rechargeable pack for power. There are also optional trays that allow to use of 8 AA (non-rechargeable). An alkaline is 1.5V fully charged, so I assume the radio can take as high as 12V.

I bought a 3S lipo pack for it, but as we all know, that charges to 12.6V. I dont want to fry my radio, so I plan to pick up a simple voltage regulator to bring the voltage down to 11V (if I can find one, I know they have 10V ones available). My controller has a built in voltage detector and starts beeping if voltage falls below 9V.

So, I figure that voltage will just hold 10/11V constant with the regulator, and once the battery voltage falls below that, then output voltage will just equal battery voltage, correct?

Basically, in short, when the input voltage to a voltage regulator is less than what the regulator brings the voltage to, it just equals input voltage? (ie, given a 12V voltage regulator, if input is 11v, so is output).

brijar · 11.12.2007, 09:29 PM

Yes, the linear voltage regulator will not do anything to the input voltage if it is less than the intended output. I would sometimes run an 8.4v pack on my Maxx when it had a 12v regulator between the pack and the fans, and it just ran the fans at 8.4v.

Good luck,
Brijar!!!

squeeforever · 11.12.2007, 09:37 PM

I don't really think the extra .6 volts will hurt it.

BP-Revo · 11.12.2007, 10:22 PM

Well...RadioCrapShack only had a 12V regulator...so If I want a 10 or 11V one I'll have to order it (and most places are charging like 4 bucks for shipping, while I paid just 1.75 for this regulator).

I'm wondering if I should just use the 12V one and see what happens? The radio is technically rated for 12V...

MTBikerTim · 11.12.2007, 11:54 PM

like squeeforever said I doubt the extra .6 volts would hurt. Can you find anyone else on forums that is using your radio with a lipo.

sikeston34m · 11.13.2007, 12:27 AM

I have 2 TQ3 Radio's that I've ran 3S Lipo in since Feb of this year.

The .6 volts doesn't hurt anything. They perform great. The .6 of a volt isn't there for the majority of the charge anyways.

Plug and Play man.

BP-Revo · 11.13.2007, 12:30 AM

Well, those are analog vs digital. I guess I'll just use the 12v regulator to be safe...

BrianG · 11.13.2007, 12:47 AM

Actually, Alkaline batteries can have more than the rated 1.5v, just like NiMHs have more than their nominal 1.2v. You'll be fine.

Also, regulators have a drop-out voltage between 0.5v and 1v. So, you'll be at less than 12v right from the start, and will only get worse as they drain. At a cutoff of 3.3v/cell (9.9v), the output of the regulator will be closer to 9v or a little less.

BP-Revo · 11.13.2007, 01:04 AM

I wonder...do radio's somehow have their own internal voltage regulator? I ask because some radio's use just 6V of input power while others use more.

glassdoctor · 11.13.2007, 01:09 AM

I run a 3 pack on my M8. It's a perfect match. 12.6v is no problem for a radio. Nimh cells are that high off the charger. Lots of guys are starting to run 3s transmitter packs.

Also, most radios have a low-voltage alert between 9-10 volts. Perfect for a 3s.

As long as you don't accidentally leave the radio on overnight.... (don't know how low the radio will continue to stay on, draining the pack but I'm assuming it will go way down... so bye-bye lipo)

Mine is a 3500mah pack so me thinks it will last a while before I need to charge it. :D

BP-Revo · 11.13.2007, 01:13 AM

Mine's only 1100mah, but on a 600mah NiCd pack my radio lasts a good 5-6 hours.

My radio starts complaining at me at about ~9v (somewhere around there). Its a constant beeping, so its quite noticeable (and annoying!). To be completely honest the biggest reason I'm switching is so I can quickly charge the pack if its low. The NiCds can only be charged by a trickle charger that came with the pack (due to plug conflicts - I can't plug em into my Ice). I'll be wiring a deans to the battery though, and if it ever runs out - I can quickly charge the majority of the capacity in an hour.

aqwut · 11.13.2007, 07:10 AM

3S works fine... I used 8X Lithium AA batteries in mine.. and it works great...
and the lithiums are like 1.7 to 1.8 volts per cell...

sikeston34m · 11.13.2007, 08:22 AM

There are alot of Lithium Cell Phone batteries out there that will fit the existing battery compartment.

One big advantage to the Cell Phone batteries is the fact that they have a pcb in the case. It will monitor the charging/discharging process. It will shut off the juice if that cell goes below 3.0 volts per cell. When it's plugged into the charger, the switch resets itself again.

If the cell is attempted to be overcharged, it will shut off the power to the cell at around 4.3 volts per cell. It's a built in safety.

Here's an example.
http://cgi.ebay.com/T-E-maxx-Traxxas...QQcmdZViewItem