RC Car Repair Pit Light & Battery Discharger

RC Car Repair Pit Light & Discharger


Hello all RC enthusiasts from around the world. I hope you are all well.

In this post, I will be showing you how I built a battery powered RC work/pit light that can be powered by RC batteries up to and including a 6S LiPo pack. It can also use Ni-Cad as well as NiMH batteries from 6 volts. It will have a LiPo safety cut off as well as a volts, amps and power display. It also will have a timer to conduct small tests, if required. All powered from the  battery of your choice, old or new. 

As I needed a new desk inspection lamp at short notice, I quickly cobbled this together in a massive hurry, hence the state of it. Hideous it is, but it does works well and packs a punch in lumens department (well enough to complete trackside repairs). I do intend to re-case this project as soon as possible, using as many reclaimed and repurposed materials as possible.

I take no responsibility for any damages or injuries caused to you or others whilst undertaking this project.  If, you do decide to follow these instructions please be careful and double check your wiring. LiPo batteries are very, very dangerous and sometimes even the qualified persons can make life changing/threatening  mistakes, see below. Please do not risk your own life or the lives of others. I am sure you have all seen photograph's of the aftermath of a battery fire, it's not pretty and is unavoidable. Lives have been lost in such fires.

You can see in the above picture, my balance leads completely melted and almost caught fire due to a small mistake I made. Basically I wasn't paying enough attention. This could have easily caught fire if it was left unattended. This is why I never leave batteries charging unattended. 

First of all a circuit diagram is needed to show you how I connected everything together. The first diagram is of an under voltage protection circuit which MUST be used when powering the light with a LiPo battery. The circuit I am using, was originally designed by another person, not myself  (DIY Perks). The circuit is available on YouTube to observe and learn for yourselves.

In the circuit diagram above shows how the LiPo cut out is wired (resistors and capacitors removed for clarity). On the right is the original design and to the left is my slightly modified design. I changed the original design as the sub miniature relays are around £14 each, due to the fact they have a high current capacity of 8 amps. However, I will be drawing no where near that amount of current for this lamp, so I used the relay on the left which still has a capacity of 3 amps but cost only £2.71 each. However either of these latching relays can fulfil the needs of this simple circuit. The cheaper relay is a Hongfa HFD2 5 volt "Latching" DPCO type. The more expensive type is the DSP-1a-L2-DC5V "latching" relay. It is important to use a latching relay as the switch will stay closed even when the power is switched off. In other relays the connections will open when the power is switched off.   The above circuit can be a little tricky to get working but you need that before moving onto the main light.

Above is a picture of the more expensive DSP 1a-L2-DC5V latching relay. At £14 each they are quite expensive, but the operating capacity of 8 amps at 250 AC is impressive. Once the under voltage protection is complete and operational, it can monitor LiPo batteries up to and including a 6S battery.   

The wiring diagram above shows how the components are wired together. The buck and boost converter can accept voltages from 5V up to 30VDC. I then set the output of the board to 12volts using the on board micro potentiometer. The buck and boost module is a 400Watt, 15amp, DC to DC automatic step up and down and cost £8.50 (see below). This particular module can handle up to and including 8S (29.6VDC).

To monitor the voltage, current and power of NiMH batteries I used an old display. The display I used was previously in another project, which I liberated. It is a Deek Robot rated at 10 amp and 100 volts.  I cannot remember how much it was, but they are still widely available. As I stated, this is to monitor other types of rechargeable batteries such as NiMH, NiCad etc. When using a LiPo battery the under voltage protection circuit monitors the battery. A picture of the display is below.

In the above picture you can see the display panel in operation, powered by a 2S LiPo battery. As you can see the output is 11.5Volts, where my meter read 12.0VDC. Calibration for both instruments is uncertain, but it is close enough for me. As you can see the power consumption is quite low as is the current. Therefore a fully charged 3000mAh battery pack should power this light for approximately 6 hours. This light has twenty one, 12 volt, 5050 packaged LED reel. Each 5050 LED has 3 LED's inside therefore, there are a total of 63 LED's illuminated. This makes a lot of focused light and is awesome for close up work. 

For connection purposes I used a JST XH adapter board (above) to connect LiPo battery balance leads. Now all the connections of the battery can be at the back, out of sight. It slightly tidies it up, slightly. It needs a case redesign as soon as possible. The adapter accommodates up to 6S and cost £3.99. With the extension connection lead connected to the under voltage protection circuit at the front, it's good to use. 

I installed a green LED timer module that was slightly damaged for time, date and also check discharge times. This is completely optional. I only used it as it was damaged and spare and I like to see the time. It is not in the wiring diagram but is easily wired up for operation. This is done by simply connecting the power leads of the module to the outputs (12VDC) on the buck/boost circuit module.  

Above is a picture of the under voltage protection module, a switch, the voltage limit  selection button and the start button. When I get time to redesign the case, all the components on display will be incorporated together and inside the case. I may also move the battery connections to the front in the new design. The switch in the picture above only opens the battery positive conductor and not the balance circuit. However, I have an idea that could and should, solve that little problem. As the switch above is a double pole, there is a spare pole that could be used to open the negative conductor of the balance lead therefore switching off both the battery supply and balance circuit with one switch and one operation or throw as it is known.

With all the wiring connected (mechanically), it was time for a test using a 2S battery. 

And it works perfectly. In fact this has been used for a number of weeks, for different purposes. I have even used it to illuminate my BBQ on an evening. Being totally portable with no wires is a blessing in the dark. Nothing to trip on and with approximately 6 hours of usefully super bright lumens, it's a must for many purposes.

 As I built this in a major hurry, it is rough but it does the task I require of it, so I am very happy with the outcome. I don't know if you have noticed, but I also adorned it with some of my favourite RC manufacturer decals. Mainly Kyosho RC decals, but there are some other support manufacturers in there too. The keen eyed among you may also notice a nod towards the Schumacher Cat XLS obviously. 

Yes, I agree it is a monster but it does what I need it to do. It was never meant to win a beauty contest, in fact I never expected to share this project with you. I needed a good, bright and reliable light. The truth is, after many hours (and I mean many, many hours), this light has never had any issue (electrical or mechanical) running on either NiMH or LiPo batteries. The under discharge circuit looks after the LiPo batteries and with the instrument measurement display, I can easily monitor the Ni-Cad/NiMH type batteries etc.  And with that ending information, the project is complete to use, but does need re-casing asap.

If you do decide to build this, please be careful and check your wiring.

I would be pleased if you enjoyed it, and I hope you join me in the next post.

Until then my friends, take care!!




Catxls said…
Thank you Laura. I will indeed continue to share my idea's with you all. Take care my friend.
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