# DC converter for gas DC generator

#### Supercaps15

Joined Feb 20, 2020
13
I searched the forums and this has been posted in many variations, but I couldn't find anything for my specific application. I am looking to build a series hybrid moped. It's just for fun. I have an engine and generator. The generator is supposed to put out 48v 31 amps at 1800rpm. I will be routing this power to a DC converter that will charge a bank of super capacitors. The voltage of the super capacitor bank is also another factor to be decided. Do I get a 24v bank and run 62amps to it?

#### djsfantasi

Joined Apr 11, 2010
6,187
Your numbers don’t match. Why are you using a 24V bank? How are you converting 48V to 24V?

#### Supercaps15

Joined Feb 20, 2020
13
Your numbers don’t match. Why are you using a 24V bank? How are you converting 48V to 24V?
The 24v number is not set. I was just throwing out ideas. Though the lower voltage is suggested for size and financial constraints.

I would need something to keep the voltage from the generator constant at whatever voltage pack I end up with.

#### djsfantasi

Joined Apr 11, 2010
6,187
The 24v number is not set. I was just throwing out ideas. Though the lower voltage is suggested for size and financial constraints.

I would need something to keep the voltage from the generator constant at whatever voltage pack I end up with.
You mean you don’t know what the voltage output is from the power bank? If you don’t know that, almost any question can’t be answered!

Before anything can be determined, you need to tell us the output voltage and current.

#### Supercaps15

Joined Feb 20, 2020
13
You mean you don’t know what the voltage output is from the power bank? If you don’t know that, almost any question can’t be answered!

Before anything can be determined, you need to tell us the output voltage and current.
I don't have a power bank yet. All I have is an engine and a generator that puts out 48v 31amps @ 1800 rpm.

I am asking for suggestions on a supercacitor bank (voltage, farad rating) and a circuit to charge it from the generator.

Joined Jan 15, 2015
5,139
The generator is supposed to put out 48v 31 amps at 1800rpm.
OK so 48 Volts @ 31 Amps works out to be just under 1500 Watts. Now in a perfect world that would be about 2 HP but since nothing is perfect you may want to figure 3.0 HP or greater. Another problem is super caps are generally low voltage capacitors and when I say low voltage I mean a maximum working voltage of about 3.0 VDC. You don't just build a capacitor bank like you can with electrolytic capacitors.

I am not trying to dissuade your plan but pointing out a few considerations. I would be thinking, if you want an electric vehicle, using LiPo batteries or look at how the new electric motorcycles are powered and work towards a hybrid.

Ron

#### djsfantasi

Joined Apr 11, 2010
6,187
I don't have a power bank yet. All I have is an engine and a generator that puts out 48v 31amps @ 1800 rpm.

I am asking for suggestions on a supercacitor bank (voltage, farad rating) and a circuit to charge it from the generator.
You aren’t getting it. To get suggestions for a super capacitor bank, you need to tell us it’s voltage output. And to get a recommendation for the Farads needed, you need to tell us the output current.

#### Supercaps15

Joined Feb 20, 2020
13
OK so 48 Volts @ 31 Amps works out to be just under 1500 Watts. Now in a perfect world that would be about 2 HP but since nothing is perfect you may want to figure 3.0 HP or greater. Another problem is super caps are generally low voltage capacitors and when I say low voltage I mean a maximum working voltage of about 3.0 VDC. You don't just build a capacitor bank like you can with electrolytic capacitors.

I am not trying to dissuade your plan but pointing out a few considerations. I would be thinking, if you want an electric vehicle, using LiPo batteries or look at how the new electric motorcycles are powered and work towards a hybrid.

Ron

Maxwell has 48v supercapacitor packs available. They have balncing circuits and are capable of over 800amps of output.

The engine I have is in fact 3HP. I have already properly sized those components.

#### Supercaps15

Joined Feb 20, 2020
13
You aren’t getting it. To get suggestions for a super capacitor bank, you need to tell us it’s voltage output. And to get a recommendation for the Farads needed, you need to tell us the output current.

I am looking to power a 48v DC motor from the super capacitor bank, so 48v would be the bank voltage.

I was hoping I could have a smaller voltage pack and boost the voltage going into the motor controller. Seeing as this is all for a series hybrid system.

#### djsfantasi

Joined Apr 11, 2010
6,187
Ok, we’re getting closer to an answer.

You still have not provided the current needed by this motor. We can’t figure it out, because it’s your motor. Remember, motors have TWO current requirements. Startup and running. Startup is usually greater and normally is what we have to design for.

If you have a smaller voltage pack, remember that it must supply a much greater amount of current. Let’s say your motor needs 5A. And you are boosting 12V to 48V. Then your source (and all of its connections) must supply more than 20A.

#### Supercaps15

Joined Feb 20, 2020
13
Ok, we’re getting closer to an answer.

You still have not provided the current needed by this motor. We can’t figure it out, because it’s your motor. Remember, motors have TWO current requirements. Startup and running. Startup is usually greater and normally is what we have to design for.

If you have a smaller voltage pack, remember that it must supply a much greater amount of current. Let’s say your motor needs 5A. And you are boosting 12V to 48V. Then your source (and all of its connections) must supply more than 20A.
Quick note here: I know how motors work. I wouldn't be attempting this if I didn't.
It's a 1200w continuous system. So 25A continuous. 50A peak for 20s bursts. According to controller specs.

A 48v supercapacitor is able to supply 800A + according to Maxwell specsheet. I really just need a circuit that will regulate the voltage from the generator to 48v, and is capable of 40A to be safe. The supercapacitor will act as a buffer for the higher bursts of amperage.

Joined Jan 15, 2015
5,139
Maxwell has 48v supercapacitor packs available. They have balncing circuits and are capable of over 800amps of output.

The engine I have is in fact 3HP. I have already properly sized those components.
Yes and Maxwell calls their modules an ultra-capacitor. They are the same modules used in electric vehicles. Here is a data sheet example and this example is not for new development use as they have newer modules. I assume you already have all the monitoring planned out like monitoring temperature and of course the cost. Since you already have things properly sized you're about done. Nothing constructive I can add. I also assume speed control and braking is all worked out.

Ron

#### Supercaps15

Joined Feb 20, 2020
13
Yes and Maxwell calls their modules an ultra-capacitor. They are the same modules used in electric vehicles. Here is a data sheet example and this example is not for new development use as they have newer modules. I assume you already have all the monitoring planned out like monitoring temperature and of course the cost. Since you already have things properly sized you're about done. Nothing constructive I can add. I also assume speed control and braking is all worked out.

Ron
Ultra capacitors and supercapcitors are the same thing. They also won't have a problem with over heating as I will be pulling 50A max and they are rated for 16x that.

The motor controller for my DC motor controls the speed, and the bike already has breaks.

Im not trying to be a know it all here, I just have done research. Im just looking for a dc regulator circuit capable of 40a so I can feed the super capacitor bank a consistent voltage.

#### djsfantasi

Joined Apr 11, 2010
6,187
*clapping* it’s only taken more than a dozen posts to get any serious information. I’m exhausted. Reloadron has said it best.

New members think they are helping themselves by “simplifying” the information. What many don’t realize is by omitting info, they are making members attempts to help overly difficult. If you want an answer, then supply all the information you have.

#### Supercaps15

Joined Feb 20, 2020
13
*clapping* it’s only taken more than a dozen posts to get any serious. I’m exhausted. Reloadron has said it best.
I don't understand why you two are so patronizing. I asked for help with a circuit to take dc voltage from a generator and regulate it to 48v that can handle 40A. Pretty simple request

#### djsfantasi

Joined Apr 11, 2010
6,187
I don't understand why you two are so patronizing. I asked for help with a circuit to take dc voltage from a generator and regulate it to 48v that can handle 40A. Pretty simple request
Possibly because you didn’t initially ask that question and as far as I can tell by skimming your posts, you NEVER asked that question.

IMHO, you are being patronizing. You were asked several times to provide that information, and ignored the requests of those trying to help you for a dozen or more posts.

I promise to no longer patronize you. I’ll ignore you instead.

#### Supercaps15

Joined Feb 20, 2020
13
Possibly because you didn’t initially ask that question and as far as I can tell by skimming your posts, you NEVER asked that question.

IMHO, you are being patronizing. You were asked several times to provide that information, and ignored the requests of those trying to help you for a dozen or more posts.

I promise to no longer patronize you. I’ll ignore you instead.
The title of the post is "DC converter for gas generator" I was wondering if it would be feasible to get a smaller bank and boost it. What the supercapacitor bank is powering is irrelevant. I gave the voltage the generator put out and asked is 24v was feasible instead of 48v. All the info was in the OP

Joined Jan 15, 2015
5,139
The title of the post is "DC converter for gas generator" I was wondering if it would be feasible to get a smaller bank and boost it. What the supercapacitor bank is powering is irrelevant. I gave the voltage the generator put out and asked is 24v was feasible instead of 48v. All the info was in the OP
OK, no 24 volt is not feasible in this case. Why do I say that? I want to power a motor, a 1.0 HP DC variable speed permanent magnet motor. At 90 VDC this motor will typically have a FLA (Full Load Amp rating of about 10 Amps and the reality is my motor under load delivering rated HP including losses between heat, friction and other losses will require 1 KW. So now what becomes easier since 1.0 KW at 48 volts is equal to 1,000 / 48 = 20.83 amps or if I half the voltage 1,000 / 24 = 41.66 amps. The idea being it's easier to make the higher voltage lower current control than a lower voltage higher current control. Additionally the same is true of the motor. Now, based on the information given if I had the choice since I have a 48 VDC generator rated for a max current of 31 amps I would go with a 48 volt system all around. I see no reason to half the voltage and double the current to get the same amount of work done.

How you choose to go about this is entirely up to you. I am merely saying how I would consider doing it based on what I know to be available. I would also be looking at weight between the engine, generator, motor and any capacitor modules to figure out if this approach is even practical. Those capacitor modules are not cheap, even the refurbished ones out there.

Ron

#### LesJones

Joined Jan 8, 2017
2,511
A capacitor bank does not behave like a battery. A battery gives a reasonably constant voltage for a large part of its discharge cycle. The output voltage of a capacitor bank varies greatly depending on it's state of charge. So a 48 volt capacitor bank would be giving out 33.9 volts (48/root 2) when it's charge is 50%. If you try to supply it with 48 volts in that state you would require an infinite current. You would require a charging circuit that would provide a constant output power until the output voltage reached 48 volts. This power would be the maximum output of the generator. The motor driver circuit would also need to give a variable output voltage (Depending on the required speed.) for a wide range of input voltages. (Depending on the state of charge of the capacitor bank.)

Les.

#### Alec_t

Joined Sep 17, 2013
10,915
I asked for help with a circuit to take dc voltage from a generator and regulate it to 48v that can handle 40A. Pretty simple request