# Help with fritzing circuit

Hi! I’m trying to make a charging circuit for my go kart using a 48volt generator connected to 4 packs of 12 volt parallel batteries. I am using the axle of the go kart to generate power while driving.

Here is the link to the generator if it helps.

You would need to provide a diagram of how the batteries are to be connected to be charged. If the 4 batteries are in parallel the output will be 12 Volts and your generator is providing up to 48V indicating you need a high power buck regulator to reduce the (varying with speed) generator voltage to the appropriate (for car batteries about 14.5 V) charging voltage. Charging specs / limits for the batteries would also be useful.

Before we get too far, is there a gas motor driving the generator (as I was assuming) or are you trying to harvest energy from dynamic braking off an electric motor? That matters because a generator isn’t the way that is typically done (I assume because it won’t work well). The electric cars do this with a bank of large (heavy) capacitors and a high current control circuit connected directly to the drive motor which probably isn’t practical nor cost effective in this case. The 3 batteries (which should be 4 to get 48V by the way, 3 will only provide a bit more than 36V) make me think they are the power source as well.If that is true they don’t charge fast enough to do much that is useful off dynamic braking and the efficiency loss from converting power to mechanical energy (via the motor) and back to electricity (via the generator) is crippling. In cars the capacitors store the energy from the back emf of the electric motor (eliminating the generator inefficiency) to give the batteries time to charge over time but that takes big expensive capacitors (I’ve seen them surplus at about \$40 each) and a high power control circuit to harvest the back emf during braking.

I’m so sorry for not providing the right details. I’ve been thinking of using this generator to provide juice for the batteries. I’m going to attach the generator with a 4:1 gear ratio on the wheel axle so it can generate while I drive.

Not a problem, if you don’t know the solution its hard to know what details to provide. So there is a gas motor that will be driving the wheels and the generator and it only needs to charge the batteries? That makes things quite a bit easier (although the voltage is somewhat of an issue). What you probably want is a boost/buck regulator that will take the varying generator voltage and either increase it (when you are going slow and the generator is producing less than the battery voltage) or decrease it (when the generator is producing too much voltage. There are a bunch of these available on Ebay, but they typically top out at about 36V (and 1 to 3A) which is a bit too low for what you need. I’d search for boost/buck regulator 48V with google and see whats available. From there its fairly simple, the input to the regulator comes from the generator and the output (set to about 42 Volts for your 3 battery configuration) should charge the batteries. Looking for a module specifically designed to charge batteries would be a good bet too, as it may need a shutoff circuit to stop charging when the battery is charged (I’m more familiar with NMIH
and LIPO batteries which both object to being overcharged than lead/acid car batteries.

Thanks for the information! Would you help me on the whole charging circuit?

I’m not sure I know enough about lead acid chargers to do that safely. A quick google search indicates that there does need to be over charge protection but I don’t know how to do it. You would be best off finding help in a forum where there are people that know exactly what they are doing (at least on the charging end). Various types of boost/buck regulators are available from ebay for 10s of \$ that will put out 48V (as noted you are going to need that because of your
generator which will give you variable input voltages which is bad for charging).

Do you know how to make the circuit in fritzing?

Making a circuit isn’t a problem, its knowing what the circuit needs to do that is the problem. A partial list of the things I don’t know:

1. can you charge series connected lead acid batteries? You can’t successfully with LIPOs I don’t know about car batteries (my experience is limited to a charger designed to charge the single battery in my car )

2. what constitutes charged? I think (but don’t know for sure) the voltage hits around 14.4 volts. Do you damage the battery if you keep charging after that point? I don’t know.

3. Do you need to limit the charging current in some way (I doubt, it I expect a car battery will take much more than your generator will provide, but I don’t know for sure).

There are probably a bunch more I haven’t though of as well. You need someone that is experienced in doing what you want to do (charging series connected car batteries) in order to insure you do this safely. Unfortunatly that isn’t me.

Ah ok! I really appreciate your time and effort to help me!