Commercial 24 volt input inverter - any ideas for 24 volt output from Volvo?

[RandyA]

On a recent trip to Goshen, IN, I visited a small but well stocked surplus outlet that I had rummaged through several times over the previous two years.

 

Still sitting on a back shelf were two Tripp-Lite PV2400FC inverters. I looked up the specs on these units last year but decided the asking price of $250 per unit was over my curiosity budget. Anyway, these are industrial inverters that will provide a frequency controlled PWM sine wave at 2,400 watts (120 volts) at a 100% duty cycle, 3,600 watts for 30 minutes and 4,800 watts for 10 seconds. The catch 22 is the input is 24 volts DC, which probably explains why no one had purchased them. A recent check of on-line prices for just one of the inverters ranged from a low of $488 to over $1,000.

 

After politely pointing out to the owner that these things had been on his shelf for at least three years I asked if he would consider a lesser price. I was totally taken aback when he said I could have both of them for $100 ($50 each).

 

Back home with the two inverters I began to run some load test with a unit powered by two 12 volt, 125 amp hour AGM batteries. The results surpassed anything that one would find in what Jack calls “A truck stop inverter”. A run-of-the-mill 2,400 watt inverter may spec a 4,800 watt surge, but the surge rating is basically useless as it is only for a few milliseconds – or how long it takes to discharge the inverter’s electrolytic capacitors. Not enough time to get a motor running – like the one in a 15K BTU A/C compressor. But guess what? The PV2400FC will start and run a RV air conditioner. It can do this because the 4,800 watt surge is for 10 seconds, not 10 milliseconds! I only need something in the area of 11 amps or 1,320 watts to keep the A/C compressor and fan running once it has started. Of course, it would take significantly more than two batteries to sleep cool overnight in a Wal-Mart parking lot. Having a 24 VDC input rather than a 12 VDC cuts the input amperage in half of what a 12 volt inverter would pull. Figuring in the efficiency loss in the conversion the DC amperage draw is about 60 amps meaning an insignificant voltage drop in 3 to 4 feet of “0” AWG copper supply cable and a slower discharge rate for the batteries. As part of my test, I ran the RV A/C for an hour without the compressor cutting out before shutting it down. The batteries recovered to 23.2 volts at the end of the test (15 minute rest), they started at 25.6 volts after burning off a finish charge of 27.6 volts after recharge.

 

So, now I want to put at least one of these beasties to good use in the Volvo – most likely as a more reliable off-grid power source to run the 6K BTU A/C in the sleeper. My first thought is to utilize the battery bank in the golf cart we usually carry on the back of the Volvo. There are six 8 volt batteries providing 48 volts. Tapping into this battery bank and using Anderson connectors to plug the inverter into a selected bank would provide two switchable 24 volt power sources at 180 amp hours each. I could even make it so that when one bank drops to 23 volts it would automatically switch to the second bank. That’s a significant amount of battery power at no additional cost (other than cables and connectors and maybe a solenoid or two).

 

I have on-hand four of the 125 amp hour AGM batteries mentioned above – a parallel/series arrangement would give me 250 amp hours (in theory, actual would be less). I have room in the front “box” under the Volvo bed for the four AGM batteries that, BTW, weigh in at 102 pounds each. I have an 8 amp, 24 volt 3-stage grid-tied AGM battery charger from some surplus hospital medical equipment that I can dedicate to charge the batteries when plugged into shore power. What I don’t have is a 24 volt engine driven alternator to recharge the batteries.

 

Currently, 24 volt, one wire, 40 to 100 amp marine alternators are available for around $100 - $125 (example here). What I need to come up with is a way to drive one of these alternators from the Volvo D12D engine. I am toying with the idea of adding a second pulley to the front of the existing Volvo alternator and making a mount that bolts to the engine to hold the 24 volt alternator. I am wide open for any other ideas or suggestions on how to mount and drive an accessory 24 volt alternator.

 

I’ve also considered building up an adjustable timer board (flip-flop) that would provide automatic switching of a pair of relays with a few blocking diodes to alternately provide 12 volts to charge each of the 12 volt AGM batteries from the existing Volvo alternator (e.g. 5 minutes battery A, then 5 minutes battery B, repeat cycle over and over).

 

Do I really need this? No – it is just another “project” that seems cool. If I do nothing more than use the GC batteries or the current AGM’s with a grid tied charger I can put one, or even both, of the inverters to good use. One will possibly be connected thru a 12/24/48 volt, 40 amp PWM solar charge controller and three 50 watt, 72 volt solar panels on the roof of my house - I have everything needed for this. Should give a nice tax credit . These units are too nice to put back on a shelf.

 

Again, any ideas for driving/mounting an accessory 24 volt alternator from a Volvo D12D engine?

 

 

 

[Steve from SoCal]

Long ago guys with hot rods drove alternators/generators off the drive shaft to clean up the front of the engine.

 

Size the drive pulley to optimize the alternator at cruse RPM.

 

Personally I don't like the idea of adding another pulley on any unsupported drive. Find a spot to mount the 24V

alternator in line on the existing drive or do something like the drive shaft.

 

Steve

[jkennell]

Possibly you need a 12V to 120V invertor to run a 120V to 24V charger??? Sorry...couldn't resist.

[Jack Mayer]

Nice inverter, Randy. The ability to handle the load peaking is one of the things that defines a "quality" inverter in my mind.

 

My next coach will be a 48 volt system, with David's battery pack in it. Driving the entire coach, including AC units. The AC units will NOT be RV units. My biggest issue in that design is a "rational" (meaning price) way to step it down to 12 volts to service things like hydraulic pumps that tend to peak out at 70 amps or so.....That is the biggest challenge at the moment. However, I "may" revert to electric drive motors and that will solve that issue. Just depends on the rig.

 

I don't have a pulley answer for you, but the mechanical experts should......

[RandyA]

Possibly you need a 12V to 120V invertor to run a 120V to 24V charger??? Sorry...couldn't resist.

Not too far off, Jeff. There are 12 to 24 volt switching inverters with a DC output available - but the amperage is low and they tend to be expensive by comparison.

 

And yes, I have pondered driving an alternator from a point next to the carrier bearing on the driveshaft. But, that would (in my estimation) require a 2-piece pulley with a heck of a big center hole - one too big for my small metal lathe that I would need to outsource. Also the idea of spending that much time with my old bones sliding back and forth under the truck isn't too exciting.

 

Still scratching my head. Right now building a flip-flop to switch a pair of relays to alternately charge each of two 12 volt batteries from the existing 12 volt alternator is the best idea my brain has come up with. Just hoping someone had a better idea or even a tried and tested solution for a mechanical approach. And Steve, thanks for the driveshaft suggestion.

[Darryl&Rita]

Often, auxiliary brackets are available for alternate mounting options. Something like this, or one of these, will mount your E-Bay alternator. Might need to add an engine pulley, plus a tensioner, and you're in business. Talk to a good parts-man to see what alternate mounts are available for your engine. Or, go hot rod.

[jkennell]

Newer CIH combines have this fancy Relay assembly that takes 2 12V batteries, keeps them split for 12V to the controls (and charging), and connects them in series for starting.

 

http://partstore.caseih.com/us/parts-search.html#epc::mr54837ar1023792bi2752468-1 Item 1...389120.

 

Don't have a clue if this would work for you...but sure sounds like what you need when running the Invertor.

 

Here is the diagram

 

 

 

[Alie&Jim's Carrilite]

Volvo has aux alternator brackets for the marine engine series. From the D3 series up. Back in the boat building days we routinely added a 3rd or even a 4th alternator, 2 each engine, for charging whatever the customer wanted. Usually we went with 3. The original alternator would charge its own starting batteries, then the 3rd would charge the "House" 24v system.

A Volvo truck dealer may/should be able to find the right bracket kit. A marine Volvo dealer would probably have on in stock or would know what your asking for.

[Dollytrolley]

We leased a couple of 250kw CAT gen sets that had a large duplex piggyback alternator that was 12 volt in front and 24 volts in the back with one pulley on the front.....wife says it won't work on a Volvo engine.....CAT Gold color would clash with the Volvo Green color......likely the CAT duplex alternator would cost more than a new Volvo engine.....or.....it's weight in Gold.....

 

Drive on......(what voltage ....today)

[ekim]

.

My next coach will be a 48 volt system, with David's battery pack in it. Driving the entire coach, including AC units. The AC units will NOT be RV units.

 

Sounds pretty interesting. How can we keep up to date with that project:-).

[Jack Mayer]

 

Sounds pretty interesting. How can we keep up to date with that project:-).

I'll publish info on it as we develop the system.....as I typically do. Or look at what David is doing to his coach....that is along the same lines. LINK

 

If/when I build this coach the roof will have nothing on it except solar panels....and the ENTIRE roof will be covered with them. No vents, no skylights, no AC units...nothing but panels.

[DamianF]

Randy, the 24 volt charger pictured in your post is an Invacare power wheelchair charger. It probably kicks out about 8 amps at 24v, and from the looks of it by age, should have a wet/gel option switch. There are newer electronic "cte" style chargers that are much more efficient (no transformer windings). If it were me, I'd run a 12 volt inverter to power a 24v charger to keep the mechanical side of life simpler. I can check to see if I have an extra cte style charger floating around if you would use ... free. They use xlr audio plugs for charge ports, with opposing pins for positive and negative, with a third pin jumpered to positive as an inhibit line. This prevents the chair from being driven. Xlr's tend to heat up sometimes, but could easily be changed out for something more capable.

[RandyA]

Randy, the 24 volt charger pictured in your post is an Invacare power wheelchair charger. It probably kicks out about 8 amps at 24v, and from the looks of it by age, should have a wet/gel option switch. There are newer electronic "cte" style chargers that are much more efficient (no transformer windings). If it were me, I'd run a 12 volt inverter to power a 24v charger to keep the mechanical side of life simpler. I can check to see if I have an extra cte style charger floating around if you would use ... free.

Wow, you nailed the charger exactly. I "think" I may have snagged it at a Goodwill store a decade and a half or more ago. I once used it to recharge the batteries in my Grandson's electric scooter until he outgrew it. Thanks for the offer of a switching style charger but I believe I can work OK with what I have on-hand.

 

Using a 12 VDC to 120 VAC inverter to power a 24 volt switching charger would work as long as the power demand of one did not exceed the other. The Invacare charger is rated 3 amps input at 120 VAC so a 500 watt MSW inverter might power it OK it the transformer voltage is high enough with the MSW. The power factor of the two existing AC powered 24 volt charger options under consideration is unknown and could be an efficiency issue. Gotta work on that to see if it is feasible.

 

Many thanks to everyone that responded to my question. Your ideas certainly gave me a lot to think about and explore. Any of them would have worked but ultimately the cost was more than the value returned. I called two big boat bone yards down by the Bay but none knew of any Volvo marine engines in the rotting hulls that could be snagged for accessory alternator hardware.

 

What I have decided to do is use an Atmel 89C2051 microcontroller as the basis for a self toggling timer to switch two Bosch style 70 amp SPDT relays on and off at 5 minute intervals. I retrieved the above from my "junque" box (I don't throw much away) so there is no additional cost involved. I found some rescued 100 amp diodes from a defunct welder - one of which will be used between the two 12 volt AGM series connected batteries for isolation when I flip charge polarity. The diode will drop my supply voltage by 1/2 volt but I doubt that it will hurt the inverter performance enough to cause concern. Anyway, each battery will receive an alternating 5 minute charge from the existing Volvo alternator - that's twice as long to achieve a full charge so I will need to make long trips . Meanwhile, I'll kick in a a 24 volt shore power charge from either the Invacare 8 amp charger or use a Xantrex 40 amp PWM solar charge controller downstream from a (again surplus) 36 volt Club Car battery charger for a higher charge rate.

 

Will it work? In theory it should but the room needed to install the inverter, four AGM batteries, shore power charger and control circuits - all of which must be vented for cooling but kept dry - will be the challenge. The under-bed box I initially planned to use will hold the 4 batteries - but not the inverter, AC charger and controller. I am looking at a spot behind the 4 starting batteries and in front of the driver side fuel tank but that will require either eliminating or relocating the 7 gallon fresh water tank for the sleeper sink (which is rarely used).

 

In reality the benefits of this project will be less than the effort expended. Additional costs with this approach are minimal, but the time invested could become significant placing components and running wires. I mess with things like this not because I need to but because can - and that is why I need to .

 

Thanks again to all that provided input.

[Scrap]

That is pretty interesting stuff Jeff. Cooper rep was showing that to us when it was coming out a few years ago but I didn't realize anybody went with it. We ended up getting a 24V Ultracap made (with the 12-24 converter in the case with its cap charger) and went that way. It sure wasn't cheaper but it packaged a lot better and hopefully the reliability turns out better. I can say for sure that engine starts RIGHT NOW! It is pretty impressive.

 

(I also gotta go totally off topic and add that the best fire we had this harvest was a new lease CNH 8230 some guys had down the road. I don't know if it is the Hillco (hillside) added part or not, but I guess they put the hydraulic cooler on the pressure side and mounted it facing the hot side of the engine. She got a pinhole leak and went up in a big fireball!)

[RickW]

I mess with things like this not because I need to but because can - and that is why I need to .

Around here there is a lot of company down that rabbit hole .... but that is what makes this place so interesting and so much fun ...

[jkennell]

That is pretty interesting stuff Jeff. Cooper rep was showing that to us when it was coming out a few years ago but I didn't realize anybody went with it. We ended up getting a 24V Ultracap made (with the 12-24 converter in the case with its cap charger) and went that way. It sure wasn't cheaper but it packaged a lot better and hopefully the reliability turns out better. I can say for sure that engine starts RIGHT NOW! It is pretty impressive.

 

(I also gotta go totally off topic and add that the best fire we had this harvest was a new lease CNH 8230 some guys had down the road. I don't know if it is the Hillco (hillside) added part or not, but I guess they put the hydraulic cooler on the pressure side and mounted it facing the hot side of the engine. She got a pinhole leak and went up in a big fireball!)

 

Yeh---CIH started using those on the 8010 I think Actually hasn't been a big issue. I've heard of a few failures, but not very many for a solenoid on a farm machine. Certainly WAY better than the ordinary starter contactor on Gleaners a few years back....I know of one new combine where they replaced 4 before it even left the dealers lot....average # of starts = 3!!! Wasn't anything else wrong, they just fell apart!

 

Ouch. Keeping my fingers crossed on the old 7720 this year...did a lot of work cause a bunch of bearings were worn out...makes one wonder about all the rest of them.