Kids Ride-On Mod

Thread Starter

Fireman1224

Joined Apr 6, 2021
8
I'm trying to make charging a 12vdc kids ride on toy a little easier and also possibly upgrade from 12 to 24vdc at a later date. The issue is that the LiFePO4 battery and NOCO charger are rated at 12vdc and if I upgrade to 24vdc I will have to be able to switch from serial to parallel wiring. I figured I could do this automatically with some sort of relay, but I'm mot experienced with circuit design. Below is a diagram of what I am thinking. Basically the relay for the 2nd battery would be managed by a switch and a relay independent of each other. If the switch is off and the charger is not plugged in, then the system is set to 24vdc. If the the charger is plugged in, then first relay (K3) is activated and disconnects the wiring harness to the toy (M2) and activates the 2nd relay (K4) such that the wiring is parallel. If the charger is not plugged in and the switch is toggled on, then the 2nd relay should activate resulting in parallel wiring. I added some diodes to try to limit surges for the relays and try to protect the battery charger in the event of a malfunction, but I'm not really sure what I need until I can get the items on the bench to test. My hope is that someone can look at the basic design and (A) confirm the design is accurate and safe, and (B) advise what changes or areas I may need to changes I should study as I'm a complete noob and am willing to do my homework and learn. Thanks in advance for the assistance!!

1653074656366.png
 

KeithWalker

Joined Jul 10, 2017
2,522
NO No No!
With the relay switched as shown, the way you have it drawn connects one battery in reverse in parallel with the other. There would be an immediate fire and probably an explosion too.
I will draw a schematic for you.
 

KeithWalker

Joined Jul 10, 2017
2,522
This should work. When the power switch is in the CHARGE position, the batteries are in paralle and the relay is off. The charger jack is connected.and the vehicle is off.
When the power switch is in the ON position, the relay is activated. The batteries are connected in series and the vehicle is connected.to the batteries.
This is just the switching diagram. I have not shown any relay suppression or vehicle wiring.

SER_PAR.jpg
 
Last edited:

KeithWalker

Joined Jul 10, 2017
2,522
Just a thought in passing: It is not a very good idea to switch between 12 and 24 volts for the drive circuitry. If it is run on one battery until it is almost depleted, switching it in parallel with a fully charged battery could be rather devastating!
 

Thread Starter

Fireman1224

Joined Apr 6, 2021
8
Just a thought in passing: It is not a very good idea to switch between 12 and 24 volts for the drive circuitry. If it is run on one battery until it is almost depleted, switching it in parallel with a fully charged battery could be rather devastating!
That makes sense. I guess my thought was that when I add a second battery, the unit would always be running off of both batteries. The switch I was going to flip was simply to activate a relay to change the wiring from series to parallel for speed purposes (I found a similar setup for an electronic bicycle). Kinda like speed 1 for slow long distance and 2 for fast sprints. I had also thought about using an arduino as a PWM speed controller to prevent destroying the plastic gears, but again, that would only be needed if I added a second battery.

I did notice that when I was moving the relays around on the computer, I failed to notice the polarity or the relay coil and thus had the negative lead for the charger going to the positive lead on the relay coil.

If I step back, and not add the second battery, would my relay idea work for the charger? My main reason for wanting the relay rather than a switch is to prevent my over anxious boys from taking off while the charger is still plugged in. My 5yo would probably be ok, but my 3yo would run me over to win the race… :D

I really appreciate you taking the time to help me with this project!!
 

Thread Starter

Fireman1224

Joined Apr 6, 2021
8
@KeithWalker

I tried to go back and use the diagram you showed me and use a relay rather than a mechanical switch for the wiring harness (labeled Motor_DC). I really wanted to see if I could get this to work or if I'm completely off base. I did try to double check the connections and found quite a few errors in my original post. Here is a newer version:

1653338864176.png
Can you advise if this is a safe option and, if so, did I miss any additional components that I need to include? I know I need a manual reset breaker for the batteries, but since I may be switching voltages I'm not really sure what to get. The original wiring harness has it connected directly to the battery, but if I have 2 batteries, do I connect one to each positive terminal?

I appreciate your advice and assistance!
 

Thread Starter

Fireman1224

Joined Apr 6, 2021
8
@KeithWalker

I tried to go back and use the diagram you showed me and use a relay rather than a mechanical switch for the wiring harness (labeled Motor_DC). I really wanted to see if I could get this to work or if I'm completely off base. I did try to double check the connections and found quite a few errors in my original post. Here is a newer version:

View attachment 267876
Can you advise if this is a safe option and, if so, did I miss any additional components that I need to include? I know I need a manual reset breaker for the batteries, but since I may be switching voltages I'm not really sure what to get. The original wiring harness has it connected directly to the battery, but if I have 2 batteries, do I connect one to each positive terminal?

I appreciate your advice and assistance!
I just realized I forgot to bypass my manual speed switch to set the system to 12vdc... Lets see if this is better:

1653340665518.png
 

KeithWalker

Joined Jul 10, 2017
2,522
The diode in series with the battery will not allow the battery to receive a full charge. What are you going to use for low battery detection? If they are discharged too low they will not recover.
 

Thread Starter

Fireman1224

Joined Apr 6, 2021
8
The diode in series with the battery will not allow the battery to receive a full charge. What are you going to use for low battery detection? If they are discharged too low they will not recover.
The batteries actually have a battery management system. This means the BMS will disconnect at low voltage. The battery charger I bought is also capable of repairing batteries. I placed the diode to try to protect the charger from over voltage. It may not be needed or correct, but I wanted to protect my NOCO GENIUS 10 charger from a 24vdc error. Any thoughts?

Thank you!!
 

KeithWalker

Joined Jul 10, 2017
2,522
The charger should protect it's self from everything except maybe connecting the battery in reverse. You can avoid that by using polarized connectors.
 

Thread Starter

Fireman1224

Joined Apr 6, 2021
8
The charger should protect it's self from everything except maybe connecting the battery in reverse. You can avoid that by using polarized connectors.
The charger already has a connector that is keyed, so it can only be connected one way. I will remove the diode from the positive side of the connector.

What about a circuit breaker? I had planned on a 12V 30A manual reset breaker connected to the positive side of each battery, but didn't know if this was right when switching from 12vdc to 24vdc. Any adivce there?
 
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