Gas Generator Hybrid Conversion

[Braddudya]

I am building an art car for burning man. The vehicle is a 20ft long "sightseeing tour bus" (2015 Marshell DN-23). It would be great to be EV all the time but I am thinking we may need an onboard generator to be able to cruise around most of the day.



What considerations do I need to consider to run a generator charging the batteries WHILE driving? Of course I can just plug the charger into the generator and then try running the cart...but maybe it isn't that simple? I would hate to burn something up trying it out blindly.

I am going to put a clamp meter on the battery leads and get an idea of how much amperage it draws at full cruising speed (5mph). I am sure the draw is high on starting but I would think 5mph shouldn't be crazy high. This should give me some ideas of potential range with and without the generator.

 

[amberwolf]

What is the expected average and max continuous wattage requirement for driving on the playa at max weight load in worst-case winds? The playa is probably harder to drive on (more watts) than pavement, so if you can do your test on a similar surface it will help you guesstimate power usage better.

You don't need to worry about peak power draws; that's what the battery will handle as it does now.

If you have a battery large enough to supply at least the peak and continuous power to the controller on it's own, then as long as your charger can supply the average amount of power, and the generator can supply the charger with the greater amount of power it needs to convert to that, the system could run continuously. The battery is then a buffer that provides peaks and spikes the charger could not withstand, and is kept charged by the generator/charger that is only loaded down if the battery drains enough from higher motor usage than usual.

Because the playa dust can get into everything and destroy mechanical stuff like fans, I recommend using fanless chargers (you may also need extra filtering on the air intake of the generator, but you can find out about that from the many regulars to BM that probably use generators there). An option for such chargers is the Meanwell LED PSUs like the HLG and ELG series, which are potted and sealed, or there are actual chargers that are fanless, too (but for the money, the MWs will probably be more reliable).

 

[PaPaSteve]

Most of the electric cars I've owned wouldn't function when it sensed the charger was plugged in.
Always an exception to the rule ...
It may require a work around.
Hopefully the batteries are in working condition.

 

[Braddudya]

What is the expected average and max continuous wattage requirement for driving on the playa at max weight load in worst-case winds? The playa is probably harder to drive on (more watts) than pavement, so if you can do your test on a similar surface it will help you guesstimate power usage better.

You don't need to worry about peak power draws; that's what the battery will handle as it does now.

If you have a battery large enough to supply at least the peak and continuous power to the controller on it's own, then as long as your charger can supply the average amount of power, and the generator can supply the charger with the greater amount of power it needs to convert to that, the system could run continuously. The battery is then a buffer that provides peaks and spikes the charger could not withstand, and is kept charged by the generator/charger that is only loaded down if the battery drains enough from higher motor usage than usual.

Because the playa dust can get into everything and destroy mechanical stuff like fans, I recommend using fanless chargers (you may also need extra filtering on the air intake of the generator, but you can find out about that from the many regulars to BM that probably use generators there). An option for such chargers is the Meanwell LED PSUs like the HLG and ELG series, which are potted and sealed, or there are actual chargers that are fanless, too (but for the money, the MWs will probably be more reliable).

Yes this is exactly what I had planned. Unfortunately I don't know what the draw is because I haven't had any batteries to test with. I just picked up some super cheap AGM batteries and we spent 30minutes of so figuring out how to cobble them into the system for a test. I see power at the contactors but I cannot get the system to switch on. The key seems like it may be dead. I will have to hotwire it to get the contactors to switch on.

I actually found some dc generators that seem to be called "range extenders" which as the name suggests could be perfect for this project. They can be purchased in 72v varieties and look like they would consume very little fuel. They don't look like they would last forever but this is not a high mileage use vehicle. This seems like a much more efficient solution than an AC generator to DC charger. The downside is that used AC generators are dirt cheap.

3KW Silent Automatic Electric Vehicle Range Extender Generator 48V/60V/72V | eBay

3KW automatic frequency conversion split. Rated power: 3KW. Electric vehicle range extender generator. One-key electric start. Automatic frequency conversion. Air cooling. Efficient and fuel-efficient.

www.ebay.com

Most of the electric cars I've owned wouldn't function when it sensed the charger was plugged in.
Always an exception to the rule ...
It may require a work around.
Hopefully the batteries are in working condition.

The busses have no batteries at the moment. They also don't seem very smart. I don't think they have the ability to detect charging. They are essentially golf carts but 20' long.

 

[amberwolf]

I see power at the contactors but I cannot get the system to switch on. The key seems like it may be dead. I will have to hotwire it to get the contactors to switch on.

<snip>

They also don't seem very smart. I don't think they have the ability to detect charging. They are essentially golf carts but 20' long.

Some golf carts do have that ability--the one I saw with it had a relay coil powered by the charger that had it's NC contacts wired between the keyswitch and the contactor coil. So when the charger is plugged into the wall it's voltage output turns the relay on and disconnects those, so you can't accidentally drive away from the wall with the cord still plugged in. Some old brushed motor forklifts do the same thing.

Nowadays they may use more complicated circuits, especially automotive EVs, but it doesn't have to be complex to work.

So...if your "bus" has such a circuit, the relay could have failed stuck "on" so that the keyswitch isn't actually turning the contactors on....

I actually found some dc generators that seem to be called "range extenders" which as the name suggests could be perfect for this project. They can be purchased in 72v varieties and look like they would consume very little fuel. They don't look like they would last forever but this is not a high mileage use vehicle. This seems like a much more efficient solution than an AC generator to DC charger. The downside is that used AC generators are dirt cheap.

If you're not going to use a charger between the generator and the batteries, you'll need to either make sure the generator has adjustable voltage and current limits so it can do CC/CV like a charger (or LED PSU), or else add a CC/CV circuit between them. If you don't, you don't have control over the charging, and have the potential to damage the batteries or even the generator or wiring, depending on which part is uncontrolled at the time and how high the voltage or current gets.

What actual voltage and current you need will be dependent on the battery you end up using, and its requirements and limitations, vs the power requirements of the system.

 

[Braddudya]

If you're not going to use a charger between the generator and the batteries, you'll need to either make sure the generator has adjustable voltage and current limits so it can do CC/CV like a charger (or LED PSU), or else add a CC/CV circuit between them. If you don't, you don't have control over the charging, and have the potential to damage the batteries or even the generator or wiring, depending on which part is uncontrolled at the time and how high the voltage or current gets.

I thought about this and I could use a solar charge controller or something to control the charge. But wouldn't the uncontrolled system be almost identical to a car alternator and battery setup? The range extenders seem to be a glorified alternator (higher voltage) mounted to a lawnmower engine. I was considering just using cheapo car batteries and the range extender.

 

[amberwolf]

If you're just using FLA batteries, then you just need the same kind of regulator a car alternator uses, except at the voltage for the whole series set of FLAs.

As long as the generator/range extender has this, to keep voltage output steady at whatever it needs to be set to for your number of series FLAs, then it shouldn't overcharge them...it will also need to be able to limit current to some degree without just shutting down (hiccup mode), in case your FLAs are far discharged when the generator is started, or else current will be as high as the G/RE can output vs the pack's resistance, so in that event the FLAs must be able to handle that kind of charge current, and so must all the wiring between G/RE and pack.

If you decide to use lithium, you'll need a more specific charger or CC/CV regulator / converter.

 

[JackFlorey]

There's a lot of roof surface on that thing. You could easily fit 1000 watts or so of solar.

What voltage is it?

 

[Braddudya]

@amberwolf - yeah that may be the way we go. That or we bite the bullet and go with standard golf cart batteries or LiFePO4 + AC generator + standard charger, and just try to charge it while running when needed.

@JackFlorey - we thought about this but we will actually have inflatable tentacles all over the roof edges and from experience solar is not ideal at burning man. The dust covers the panels pretty quickly and then they do t put out much power at all. It would be cool to build some kind of wiper but that seems unrealistic for this project.

 

[fechter]

The roof on that car looks ideal for solar panels. While more expensive than a generator, it would be a lot quieter.

If an on-board generator is connected directly to the battery, there should be no issues with the controller locking out.
Any idea what the original battery voltage on the car is?

 

[Braddudya]

The roof on that car looks ideal for solar panels. While more expensive than a generator, it would be a lot quieter.

If an on-board generator is connected directly to the battery, there should be no issues with the controller locking out.
Any idea what the original battery voltage on the car is?

The dust is a killer for solar. It doesn't take long to be down to 20% output in full sun.

It's 72v and we actually got one running with some little used AGM batteries. Not a good long term option but they are great for proving that the drivetrain is good!

 

[JackFlorey]

The dust is a killer for solar. It doesn't take long to be down to 20% output in full sun.

We had a 3200 watt system last year and never got more than 2000 watts at noon, even after a week (and with no cleaning.)