Buck converters

[Dan1]

Hi,
I have a gas powered 120 volt inverter generator that also has a 12v 8.3 amp output (it actually shows 19v with no load)

I have a question regarding buck converters, I have a very basic knowledge of how they work however I’m getting confusing results when I google the specific question when searching for answers.

I want to run a 12 volt DC fan from the outlet ( a car radiator fan) looking at the specs of the various fans I can use they range from 6 to15 amps draw @ 12 v. I’m unsure what load a buck booster would put on the supply (the generator) when everything is connected, I don't want to overload the supply.

So a 12vdc 8.3 amp charging system from generator to a 12 volt battery to a buck converter to a 12vdc fan.

If for example using this buck converter and fan with 7.6 amp draw (12.7 amp draw at start up) will it work? Is there a better way of doing this?

https://www.amazon.com/Cllena-Autom...ZNCQ/ref=cm_cr_arp_d_product_top?ie=UTF8&th=1

Thanks, appreciate any guidance

 

[SeaGal]

So a 12vdc 8.3 amp charging system from generator to a 12 volt battery to a buck converter to a 12vdc fan.

A buck / buck-boost converter is used for lowering or increasing a voltage. If I understand your question correctly and you want to power a 12V fan from a 12V supply then no buck converter is needed.

 

[Daddy Tanuki]

no need, i ran two of the generic 12 volt fans in series on my yamaha genset for my camper. (sound deadening cabinet with cooling fans...) I also run one single for my shop when not using solar. the 19 volts you see is no load which settles down to about 14-15 when engaged... no worries.

 

[Dan1]

no need, i ran two of the generic 12 volt fans in series on my yamaha genset for my camper. (sound deadening cabinet with cooling fans...) I also run one single for my shop when not using solar. the 19 volts you see is no load which settles down to about 14-15 when engaged... no worries.

This is exactly what I'm doing, maybe I'm overthinking it.. however Iv'e read the 12vdc output on the inverter generators can be damaged when overloaded or the generator may simply go into an overloaded state and trip the circuit breaker.

There's no shortage of vid's on you tube with the fan/s being directly connected to the generator , I'm unsure what the long term result is, what fans did you use?

Seagal/Tanuki, thanks for the super fast responses!

 

[RCinFLA]

The 12vdc output from generator is unregulated. It is just a separate alternator winding that is rectified and unusually unfiltered.

Its output voltage is load dependent. It will overcharge battery if left unattended.

You can put a buck converter on 12v gen output but have to recognize there will be a load level which will drag down the generator 12v output voltage below the voltage necessary to run the buck converter. It is okay as long as you stay below that load level for buck converter output current.

You want to select a buck converter that has low dropout voltage, meaning lowest required input voltage overhead required above its regulated output voltage setting. This is a synchronous buck converter.

Alternately, you can use a buck-boost converter. They have a bit less conversion efficiency.

 

[SeaGal]

It is just a separate alternator winding that is rectified and unusually unfiltered

and may also only be half-wave rectified.

however Iv'e read the 12vdc output on the inverter generators can be damaged when overloaded

I would like to think that the generator will have a suitably-sized fuse on its dc output - if not, an overload would likely damage the rectifying diode(s) on that output.

Still trying to get my head around what @Dan1 wants to charge - is it LiFePO4 or LA battery? A standard 12V car battery would normally be charged at around 13.8V.

 

[Dan1]

Thanks RC
Its a new generator, Ive read the newer ones have a regulated supply to charge the battery, so I called tech support to ask the question

Me -- Next question is regarding the 12 volt 8.3 amp outlet. Is that outlet able to sustain a 5 amp load continuously?

Answer 8.3 Amps of DC current may be drawn from this receptacle. Use this outlet to charge 12V automotive type batteries ONLY

Me-- are you saying that because its unregulated?

Answer No, it is regulated. The receptacle will not go any higher then 12V and 8.3amps

Me-- thats fine, can the generator sustain a 5 amp load continuously from the receptacle

Answer If what you are connecting requires 5amps it will only produce the required amount. The receptacle can go up to 8.3amps. As long as you do not exceed the 8.3amps. That is continuously unless you overload the generator.

And that contradicts what I saw across the battery (19v) when running…

if not, an overload would likely damage the rectifying diode(s) on that output.

Thats my concern!

Still trying to get my head around what @Dan1 wants to charge

I want to charge the 12v lead acid battery and run a 12v dc circulation fan from 12v outlet.

I would like to think that the generator will have a suitably-sized fuse on its dc output

It does, however there is no info on its rating on the generator or in the operators manual

Thanks for your responses

 

[SeaGal]

My thoughts...

Answer 8.3 Amps of DC current may be drawn from this receptacle. Use this outlet to charge 12V automotive type batteries ONLY
Me-- are you saying that because its unregulated?

Agree. I would assume they only say automotive batteries because it is not dc as we know it... i.e. possibly only half-wave rectified and little or no smoothing capacitor.

Answer No, it is regulated. The receptacle will not go any higher then 12V and 8.3amps
...
And that contradicts what I saw across the battery (19v) when running…

Put a voltmeter on it with no load and measure it, then put resistive 55W 12V car bulb load and see what happens. Interesting if you have a scope to see any ripple too.

If it is regulated to 12v it is useless to charge a 12v battery - you need a higher voltage to put current through the battery.

I would like to think that the generator will have a suitably-sized fuse on its dc output

It does, however there is no info on its rating on the generator or in the operators manual

That's poor show! But assume you can just unscrew the fuse holder and take a look what the fuse says on it?

 

[Dan1]

I went back over the chat with Tech support and can see where there was confusion with the answers, after another chat I got this info

To clarify
There is two DC outlets, one is only for maintaining the internal battery with an external charger (not supplied) that plugs into mains power when the generator is not in use.

Second outlet is for as they put it “for automotive battery charging only” and what they mean by that is for charging an external battery, this is the outlet they refer to as 12v 8.3 amps, it is also where I picked up the 19v when testing. They referred to it as a taper charger and recommended it be disconnected after 30 minutes,probably to avoid cooking the battery.

RCin FLA nailed that!

Its output voltage is load dependent. It will overcharge battery if left unattended.

Doing more research on the subject (it’s been asked plenty of times on the net) is pretty much covered in this from Polaris about there inverter generators - the wording is very similar with other brands.

https://www.polarispower.com/en-us/self-help/article/KA-02201/#:~:text=The DC receptacle on your,designed to operate DC motors.

Yet many have done it successfully including Tanuki on this thread

no need, i ran two of the generic 12 volt fans in series on my yamaha genset for my camper. (sound deadening cabinet with cooling fans...) I also run one single for my shop when not using solar. the 19 volts you see is no load which settles down to about 14-15 when engaged... no worries.

This is an example of what I'm wanting to build, the fans he used however are 120v

Thanks to all for the responses

 

[Daddy Tanuki]

I went back over the chat with Tech support and can see where there was confusion with the answers, after another chat I got this info

To clarify
There is two DC outlets, one is only for maintaining the internal battery with an external charger (not supplied) that plugs into mains power when the generator is not in use.

Second outlet is for as they put it “for automotive battery charging only” and what they mean by that is for charging an external battery, this is the outlet they refer to as 12v 8.3 amps, it is also where I picked up the 19v when testing. They referred to it as a taper charger and recommended it be disconnected after 30 minutes,probably to avoid cooking the battery.

RCin FLA nailed that!

Doing more research on the subject (it’s been asked plenty of times on the net) is pretty much covered in this from Polaris about there inverter generators - the wording is very similar with other brands.

https://www.polarispower.com/en-us/self-help/article/KA-02201/#:~:text=The DC receptacle on your,designed to operate DC motors.

Yet many have done it successfully including Tanuki on this thread

This is an example of what I'm wanting to build, the fans he used however are 120v

Thanks to all for the responses

TLDR; I ran the two fans for 3 camping seasons and the yamaha genset I had did not have any issues.

sorry out at my cabin and cell reception hence internet is spotty.

I built a quiet box that I dropped over my genset with two fans one pulling one pushing. the genset was a yamaha 2.8 kw inverter type and it was reasonably quiet compared to any contractor models, but I wanted something quieter for boon docking (this was 15 years ago and i was just starting to explore solar. )

so my box was thin sheets of veneer coated with FRP resin to keep it from getting funky, the inside was lined with sound proofing foam blocks the exhaust exited with the hot air after a couple of baffles and overall it dropped the noise level down to a reasonable level for daytime/early evening but still too loud to run overnight in my opinion.

the fans I used were a pair of 8" fans commonly sold on amazon as auxiliary cooling fans for various hot rod projects. I wired them in series which slowed the speed of the fans down and made them quieter as a result. I ran this setup for three seasons before the genset got stolen from my house when I forgot to chain it up. By this point in time my solar charged battery system on the camper could run the spot a/c for about 6 hours with no sun before the inverter would shutdown. so I never bothered to invest in another genset for the camper.

that genset would initially run 4 hours daily in the am charging the batteries up and letting solar take over. but as my battery and solar panel system became more refined the last two seasons I only ran it for about 2 hours a day in the early morning to bulk charge, heat water for morning shower and hot coffee etc. everything after that was solar. when it got stolen i had jsut closed on the purchase of my cabin and I kind of lost interest in the camper and started building my solar system for the cabin instead.

 

[Dan1]

TLDR; I ran the two fans for 3 camping seasons and the yamaha genset I had did not have any issues.

Thanks for the response, I guess it's a hit or miss scenario as to whether or not the components can handle the load depending on the make of the generator. Like yourself, many have done it without issues.

I got this info from another forum, it may be useful to others.

The 12VDC output port (which is different from the charger port) is limited to 8.3 amps. It is not a very stable output voltage, nor is it current limited except by the breaker. However, sometimes breakers do not act fast enough to prevent damage due to such things as a short circuit. The windings for the DC Coil could be damaged if the breaker did not act fast enough.

If you are wanting to have regulated 12VDC to use, you could get the 6AMP version of the buck/boost regulator. According to its listing, it has Over-load, Over-current, Over-temperature, Short-circuit, Over-voltage protection which would be far better than just a breaker. I wouldn't go larger than the 6A regulator because you have to consider that the efficiency of the regulator will cause some loss of available output current. The 6A regulator should not overload the DC Coil. Hopefully, Firman put some buffer into that 8.3A limit and the 6A regulator would be safe to use.