• Post Reply Bookmark Topic Watch Topic
  • New Topic
permaculture forums growies critters building homesteading energy monies living kitchen purity ungarbage community wilderness fiber arts art permaculture artisans regional education experiences global resources the cider press projects digital market permies.com all forums
this forum made possible by our volunteer staff, including ...
master stewards:
  • Nicole Alderman
  • raven ranson
  • Jocelyn Campbell
  • paul wheaton
  • Devaka Cooray
stewards:
  • Burra Maluca
  • Miles Flansburg
  • Julia Winter
garden masters:
  • Dave Burton
  • Anne Miller
  • Greg Martin
gardeners:
  • Joylynn Hardesty
  • Mark Tudor
  • Pearl Sutton

Building a 24v Generator to charge a 24v battery bank  RSS feed

 
Posts: 81
10
chicken goat purity
  • Mark post as helpful
  • send pies
  • Quote
  • Report post to moderator
Okay.  So we're thinking of upping the 12v system to a 24v system.  We have only 1 need for direct 12v power; a few 12v lighting strips.  So I figure we can meet that need by either using a low-amperage step-down transformer to supply 12v power from the 24v bank, or run a line from the charge controller's accessory port to a switch or series of switches that will supply 12v power to these light strips.  We have multiple MPPT charge controllers that are variable 12/24v and have 6v and 12v accessory ports.  Our panel setup is 810watts / 24v (really 45v of course).

The major kink with going to a 24v system seems to be charging the batteries with a generator when the sun's been gone too long.   I can't find any sources for high amperage (over 10amps, at least) step-up transformers, so I tossed out that idea.  I found some info on building a large transformer yourself but I don't want to do that.   We are actually about to build 2 generators (using 200cc motors) ourselves, and I thought, well, why not make one a 24v generator?

I haven't been able to find much literature on 24v generators.  My options, so far, appear to be the following:
1.  Use a 12v alternator, run the power through a regulator that bumps it up t o 24v, which the alternator should be able to supply- BUT this will likely burn up the alternator / shorted its life
2.  Wire x2 12v alternators in series to produce 24v power.  That's twice the alternator expense though, and complicates the generator build.  
3.  Use a 24v diesel engine alternator.  I can't find any info on doing this but I can't see where it'd be an issue?  I'd only need half the amperage rating as compared to a 12v alternator, so I wouldn't need a heavy-duty one, if I'm not mistaken.   Could it be as simple as swapping the alternators out or am I missing something?



Any thoughts?  Pro's/con's of 24v generator build?  Anyone tried this?
 
pollinator
Posts: 623
Location: Victoria BC
35
  • Mark post as helpful
  • send pies
  • Quote
  • Report post to moderator
I haven't done this, but read up a bit, a while back.

A 24v alternator or a heavy duty 12v with 24v regulator should both work alright, the trick is not burning them up with excessive speed.

With the regulator swap, for clarity, it is not that you would be generating 12v at the alternator and then running it through the 24v regulator to step it up; replacing the 12v regulator (assuming it was there..) with the 24v regulator means the alternator will be putting out 24v. (nominal voltages..)

The remaining drawback is that your average 24v regulator is not going to do a great job charging deep cycle batteries. There are 3-stage regulators meant to do this much better. (Balmar, xantrex... mastervolt?) These are marine products, generally, so there is probably some sticker shock involved...

2 alternators in series does not seem like any sort of good idea.


This instructable has an interesting take on the matter. Note how hands-on the charging process is...

https://www.instructables.com/id/Off-Grid-LPG-Battery-Charger/


I ended up deciding an AC generator, while less efficient for batt charging, was sufficiently more flexible to be preferable. I can use it to run the tablesaw or compressor instead of firing up the huge shop generator. I also charge the laptop and up to 5 powertool batteries at the same time that I'm topping off the 24v battery bank.
 
Posts: 120
Location: North central Ontario
4
  • Mark post as helpful
  • send pies
  • Quote
  • Report post to moderator
Alternators provide wild 3 phase ac the regulator does the rectifying and voltage control. if you are going to build a alternator based generator get one geared from the work go for 24 volts. I purchased this one:
https://www.amazon.ca/gp/product/B0081SBDCM/ref=oh_aui_detailpage_o00_s00?ie=UTF8&psc=1
I only ran it 4 times and have removed it and stored the parts as I needed the engine for a snowblower. It worked fine. I upgraded to a magnum inverter with a charger so didn't need it any more. Some cautions:  alternators are made to charge a small battery fast then slow down not always the best for deep cycle. At 40 amps I was charging a 400 amp hour battery bank  so that is a c10 rate, which is ideal. That kind of sustained amperage on an alternator is hard so they usually recommend a heavy duty or marine unit. Also you must turn a one wire fairly fast to get it to self energize. The older 2 wire units are good as well you can adjust charge amps with a resistor. They can turn a little slower but you need the rpms to turn the fan fast enough to keep it cool. Recommended RPM is usually in your specs.  Alternators are not good at 3 stage charging and loose efficiency as a battery gets close to full so think of it as a bulk charger only let the solar do absorb and float...
Here is the base article I used this one is a 12 volt 2 wire but 24 volt single wire is mostly the same. Its an oldie but a goodie from Home power magazine when it was more then just what gear to buy... All the other articles I've found online are derivatives of this one.
https://www.google.ca/url?sa=t&rct=j&q=&esrc=s&source=web&cd=7&ved=0CFkQFjAG&url=http%3A%2F%2Fwww.homepower.com%2Fsites%2Fdefault%2Ffiles%2Fuploads%2Fwebextras%2Fmark8.pdf&ei=m70uUf_aOYK8yAGihYGYAw&usg=AFQjCNFSSinc1_FuS_mj2lM9RAjsn6dzwA&sig2=WtkyXcTaagzdtdXrsZukog
You could also just buy an iota charger for the same money which does three stage charging and power it with a 1500 watt ac generator also pretty common and cheap. Home built is always more fun though!!!
Hope you build one.
Cheers, David
 
pollinator
Posts: 596
Location: Southern Arizona. Zone 8b
77
bee bike fish greening the desert solar woodworking
  • Mark post as helpful
  • send pies
  • Quote
  • Report post to moderator
Large truck (Semi's) use 24V systems, including 24V alternators.

Also, when searching for solutions, it often helps if you use the correct terms.  "Transformers" only work with AC circuits, for example standard 120V /240V systems.  Transformers do NOT work with DC systems (batteries).

You use "DC to DC converters" to go from one DC voltage to another.  Specifically a "Buck" converter to reduce voltage and/or a "Boost" converter to increase voltage. Perhaps a Buck/Boost if you need one that can do either.

Final thought.  Alternators (cars or trucks) will happily produce over 100V.  As you know, the regulator controls the voltage, replace the regulator you can change the voltage.  Unless you get way over 100 volts, what damages alternators is pushing too much current through them not the voltage.
 
Jen Fan
Posts: 81
10
chicken goat purity
  • Likes 1
  • Mark post as helpful
  • send pies
  • Quote
  • Report post to moderator
Thanks for all the input!

To clarify, we already use a charge controller on our generator to charge the batteries.  It handles the 3-stage charging.  Basically the generator supplies a high amerapge charge controller, like the solar panels would, and that is then used to charge the bank.  So the problem of 3-stage charging is taken care of.

On the transformer/regulator terminology; I learned it as regulator, but in all this research I've been doing I kept seeing the terms intermixed.  Even when shopping for DC regulators, many of them are also called transformers in the same item description.  So thank you for the clarification.

We've already purchased 2 12v alternators (before we started thinking about a 24v system).  We did our research on a model that was built to actually sustain its rated amperage.  So we're hoping to find a 24v alternator that is built tough enough and large enough to sustain a higher amperage output.  Ours is a 450ah bank, so we don't need crazy high amperage, 10-15 would suffice.  
It's sounding like going with a 24v alternator might be the best choice here.  We just need to figure out which unit can endure this application!  Any input or experience on that?  

David B;  thanks for the product recommendation.  I'm researching this model.  And you gave me a good chuckle!  I followed your link and tried navigating Amazon further and got in a tizzy "WHY DOES AMAZON THINK I'M IN CANADA".  Hahahahaha!  Thanks
 
Peter VanDerWal
pollinator
Posts: 596
Location: Southern Arizona. Zone 8b
77
bee bike fish greening the desert solar woodworking
  • Mark post as helpful
  • send pies
  • Quote
  • Report post to moderator
If it's a 450AH bank, you'd want at least 45 amps of charging to keep it healthy.   In general, lead-Acid batteries work best when charged at their C/10 rate (capacity / 10), at least for the bulk charging phase.
 
Jen Fan
Posts: 81
10
chicken goat purity
  • Mark post as helpful
  • send pies
  • Quote
  • Report post to moderator
Good to know, thanks Peter
 
Jen Fan
Posts: 81
10
chicken goat purity
  • Mark post as helpful
  • send pies
  • Quote
  • Report post to moderator
We keep bouncing back the idea of running 2 alternators in series.  It seems like running 2 12v alternators to supply the 24v power would equate to less work per alternator, kind of splitting the load between the two so that it's easier work for them.  Does that sound reasonable?  
 
pollinator
Posts: 2116
Location: Massachusetts, Zone:6/7, AHS:4, Rainfall:48in even Soil:SandyLoam pH6 Flat
95
forest garden solar
  • Mark post as helpful
  • send pies
  • Quote
  • Report post to moderator
Is your current system 450AHr times 12V = 5400WHr = 5.4kWHr
If so your future system will be 225AHr times 24V = 5400WHr = 5.4kWHr
Can you clarify?

But lets go with your quoted 450AHr times 24v = 10.8kWHr
You are going to need a generator that is outputting  45A * 24V = 1080W (1.5hp)
So the engine should be 1.5hp*2= 3hp
The alternator efficiency is 60% and it would be best if the engine was only at 60% so more like 1.5hp*3=4.5hp


I see an alternator that does 24v and 40A
https://m.autozone.com/starting-charging-and-miscellaneous-electrical/alternator-universal/remy-agricultural-alternator/75978_0_0?review

I see lots of 12V * 140A alternators for sale here.
https://www.autozone.com/batteries-starting-and-charging/alternator





 
Dillon Nichols
pollinator
Posts: 623
Location: Victoria BC
35
  • Mark post as helpful
  • send pies
  • Quote
  • Report post to moderator
What is the max output of the MPPT controller?

If it's at all likely to receive more power than this, what is the expected behavior when it has excess incoming power; burn up, or self-limit?

The below post mentions getting more than rated power from alternators used as described with an mppt controller; by virtue of the lack of a 24v battery connected, the alternator ends up putting out notably higher voltage. This is likely perfectly fine for the mppt controller, as long as the resulting higher amperage and hence higher wattage don't become excessive... or, if the unit is equipped to handle excess power by limiting output.

https://forums.energymatters.com.au/wind-solar-misc/topic6042.html
 
Jen Fan
Posts: 81
10
chicken goat purity
  • Mark post as helpful
  • send pies
  • Quote
  • Report post to moderator

S Bengi wrote:Is your current system 450AHr times 12V = 5400WHr = 5.4kWHr
If so your future system will be 225AHr times 24V = 5400WHr = 5.4kWHr



We currently have x4 12v 225AH batteries, which would be combined into x2 24v 225AH batteries.


S Bengi wrote:
But lets go with your quoted 450AHr times 24v = 10.8kWHr
You are going to need a generator that is outputting  45A * 24V = 1080W (1.5hp)
So the engine should be 1.5hp*2= 3hp
The alternator efficiency is 60% and it would be best if the engine was only at 60% so more like 1.5hp*3=4.5hp



The motors are 6.5hp, the heavy duty alternators we have currently are rated 100amp.
 
Jen Fan
Posts: 81
10
chicken goat purity
  • Mark post as helpful
  • send pies
  • Quote
  • Report post to moderator

Dillon Nichols wrote:What is the max output of the MPPT controller?

If it's at all likely to receive more power than this, what is the expected behavior when it has excess incoming power; burn up, or self-limit?

The below post mentions getting more than rated power from alternators used as described with an mppt controller; by virtue of the lack of a 24v battery connected, the alternator ends up putting out notably higher voltage. This is likely perfectly fine for the mppt controller, as long as the resulting higher amperage and hence higher wattage don't become excessive... or, if the unit is equipped to handle excess power by limiting output.

https://forums.energymatters.com.au/wind-solar-misc/topic6042.html



Our current generator is actively wired through its DC plug port to a 60amp mppt controller.  All of our controllers allege that they disperse excess power through the controller body as heat.  I've never knowingly overloaded one, so how they truly function I do not know.  Our panels flow through 40amp controllers, though they're never handling that much.  They might if our panels produced their full potential, but our current setup does not allow for that.  We get about 50-70% efficiency from them at the moment.

 
S Bengi
pollinator
Posts: 2116
Location: Massachusetts, Zone:6/7, AHS:4, Rainfall:48in even Soil:SandyLoam pH6 Flat
95
forest garden solar
  • Mark post as helpful
  • send pies
  • Quote
  • Report post to moderator
Thanks for the clarification.
Can you send a link to the manual/documentation for the alternators that you currently have.

Also I am confused if it a alternator with AC sine wave power
Or if it is a generator with DC/rectified power.
If it is noisy AC it will be super hard to combine two in series, due to phase.
But it will be easy to use a simple transformer to change just 1 from 12V,100A to 24V & 50A.
And that would be 1200W which would provide all the power that we need.
You would have to change that it from AC to DC for the charge controller.
If it is in fact DC/generator vs an AC/alternator then it would be simpler to combine two in series.

Charge controller can deal with "excess" solar panel energy very easily.
But when it comes to Hydro/Wind/Engine DC power it does need a dump load.
I have never seen one with it built in but they are always releasing new things.
Can you send a link to the Charge Controller manual/documentation.
I love seeing what "new" products gets release.

Next will be setting up the 6.5hp engine to only output 1.5hp (1080W = 24V*45A)
What is the optimal RPM/torque for engine life vs fuel efficiency.
Hopefully you will not be using the generator too much for you to even worry about it.
How often do you see yourself needing to use the generator/alternator.
12 times a year (once a month) or is it more like 52 times a year (once a week)?
  • Post Reply Bookmark Topic Watch Topic
  • New Topic
Boost this thread!