Switching extra 12v battery between parallel 12v to series 24v for Kids Power Wheel car.

clone477

Joined Oct 3, 2008
28
It has been years, probably 7 years since I have been one here, amazing resource, hope you guys can help me with me sure up....

To make a long story short, my sons little power wheels electric car is 12v. I figured out the wiring diagram but obviously missed something.
My goal is to add another 12v batter with the same Ah rating as the first, and use a switch to switch between having the 12v batteries in parallel(for double drive time) or series for 24v for a quicker top speed.

Please ignoring all the safety issues, or frying the motors as I will be ensuring this is a safe toy, but please help me figure out where I went wrong with this wiring.

What is happening after I wired it all up, is when the on/off toggle if off(open), and the system is in parallel, every seems to work perfectly. The problem happens when I toggle on the circuit, and one relay starts chattering and only delivers 3v or so to my motors.

I suspect I might be missing a diode but have burned my brain out trying to troubleshoot this.

I also assumed the primaries on my relays can handle 24v, if I am wrong I will just wire a resistor in series to drop the voltage closer to 12v(what I am thinking)

Please enlighten me guys, I know there are guys much smarter than me on here. Thank you

AlbertHall

Joined Jun 4, 2014
11,318
When the relay contacts operate, they break the existing circuit and then, after a short time, make the other contact. This means that during the switching time the voltage is zero.
Maybe :
The voltage is 12V. You operate the switch, the relays begin to move but that temporarily disconnects the voltage and the relay drops out again. Now the voltage is back to 12V and the process repeats.
You could try a diode in series with the relay coils and a capacitor across the coils to store enough to hold the relays while they switch. For the capacitor try 100uF to 1000uF - depends on the coil resistance and how fast the relays are.

clone477

Joined Oct 3, 2008
28
When the relay contacts operate, they break the existing circuit and then, after a short time, make the other contact. This means that during the switching time the voltage is zero.
Maybe :
The voltage is 12V. You operate the switch, the relays begin to move but that temporarily disconnects the voltage and the relay drops out again. Now the voltage is back to 12V and the process repeats.
You could try a diode in series with the relay coils and a capacitor across the coils to store enough to hold the relays while they switch. For the capacitor try 100uF to 1000uF - depends on the coil resistance and how fast the relays are.
Albert I think you may be right, that makes does make sense. Thank you. So I will have diode on positive trigger wire to relay coil, then after that put a capacitor across the positive and negative coil, correct? Thank you

SaleB

Joined Jul 3, 2017
7
I have at hand no better drawing solution, but I hope the diagram is clear. You can use two separate relays activated and deactivated simultaneously. The relays must have Normally Open (NO) and Normally Closed (NC) contacts (SPDT). In disengaged state you get a series connection and in active state you get parallel connection. Alternatively you can use DPDT relay which combines both "switches" in the same case. Alternatively you can also use a simple DPDT switch which is rated at the power (current) that you need.

clone477

Joined Oct 3, 2008
28
Thank you for the other wiring suggestion looks much easier than what I already wired.

I have pinpointed the problem after the suggestions from Albert, but do not know why.

I simply jumped power to the positive side of the primary coil in the relay, and both relays still chatter/buzz. I then separated the two relays(they were being fed by the one wire, and jumped power to each primary relay coil independently, and they work perfect.

So how will they not work when attached together to the same trigger wire, and how do I fix this? Thank you guys.

clone477

Joined Oct 3, 2008
28
Mannn I'm sorry for all these posts, but we can close this thread and thanks to all that helped. Its 2:30am, I can't sleep when I can't solve things. Following alberts suggestion I jumped a capacitor across the primary energizing coil of the relay, and problem solved! Maybe self oscillating? I don't know but some feedback going on. Thank you all!

Tonesaul

Joined Dec 13, 2018
7
Just a clarification. Did you mean substitute his batteries in place of the motors in the diagram?
The originator of the question has two 12v batteries i believe. I am going to replace each motor with a 12v battery. The two leads that come out the top would then connect to your motor that could take either 12v or 24v. Agree?

djsfantasi

Joined Apr 11, 2010
7,700
The originator of the question has two 12v batteries i believe. I am going to replace each motor with a 12v battery. The two leads that come out the top would then connect to your motor that could take either 12v or 24v. Agree?
Agree! Your original wording was not clear to me on this point.

Tonesaul

Joined Dec 13, 2018
7
Agree! Your original wording was not clear to me on this point.
Hope it works. Let you know.

Tonesaul

Joined Dec 13, 2018
7
It works far better than i imagined. My reason for converting between 12v and 24v was to make use of old boat batteries in the shed. Reluctant to throw them away i have them charged by a wind turbine and an old solar panel. They are connected to some led lighting. However i don't use the shed very often and these batteries remain pumped up....even possibly overpumped at around 13v. On our narrowboat next to the shed we often run our batteries low with lighting, pumps and TV. I have connected a line from the shed batteries to the boat batteries but the 13v to say 12v slope only trickles less than 0.2 amps across the considerable length of wire. Switching the batteries to 24 has negated all my problems and allowed me to put the leads through my boat solar regulator. Switched thet DPDT to 24v yesterday afternoon and hey presto... I'm over the moon. Would you believe initially 11.7 amps flowed into my boat. Glad i did over kill with the wiring for the batteries and switch. 17amp wire used. I though i had my meter switched to volts not amps to start. Ha. Just remains to see how many amp hours my batteries in the shed can deliver when i need the boost.