24 V DC to AC Inverter

[dmanda24]

I have some 24V dc to ac inverters they are sinewave inverters, not rectified sine like most cheap inverters, they were used to power cellphone sites, they have automatic transfer, and a whole bunch of other whistles. anyway they are just occupying space and I was thinking of installing the smaller one (4000 W) to the Van, and putting in and extra battery with a double pole double throw switch for being able to put the batteries in parallel for charging and in series for using the inverter. Any recommendations or precautions. Are there any implications on the alternator for adding another battery? All advice is welcomed

[mdshunk]

You will need to get (or rather, should get) a battery isolator to charge the second battery off the alternator. It's basically 2 big diodes, mounted in one heat sink. It has three posts. One for the alternator, a second for the battery A, and a third for battery B. You should also jump up a size or two on your alternator, since a typical stock one will self-destruct trying to charge two batteries if you run them pretty low while using the inverter before starting the engine.

[dereckbc]

Just curious what brand and model are they?

[dmanda24]

would I still need the DPDT switch?

[dmanda24]

Just curious what brand and model are they?

Exeltech, and the model im not quite sure since its a module assembly it has 4 mx100 power modules, a control card a transfer switch card an alarm card, I know they are pretty expensive, I looked it up when I got them, but I don't remember anymore, I was planning on getting some solar panels to hook them up to the house, but haven't done it yet, maybe this year, hurricane season is upon us.

[dereckbc]

Couple of notes to yourself in addition to the isolation diodes.


The wire or cable to the inverter will need to be very large and kept short as possible to prevent voltage drop at 24 VDC. If you pull the full 4000 watts will translate to 170 amps @ 24 VDC

The other problem will be battery capacity and battery life. Auto batteries are not made for this purpose. Auto batteries are made for short burst of current to start a car, not prolonged deep discharges. The other issue is capacity. If you use a auto battery they are in the range of 45 to 60 AH or about 500 to 700 watt-hours. That isn't much time when connected to a 4000 Watt inverter, and running a skill saw off of it. You could find yourself needing a jumpstart at the end of the day when it is time to go home.

Last point the two batteries will need to be exact make and models to be series and/or paralleled.

[dmanda24]

Couple of notes to yourself in addition to the isolation diodes.


The wire or cable to the inverter will need to be very large and kept short as possible to prevent voltage drop at 24 VDC. If you pull the full 4000 watts will translate to 170 amps @ 24 VDC

The other problem will be battery capacity and battery life. Auto batteries are not made for this purpose. Auto batteries are made for short burst of current to start a car, not prolonged deep discharges. The other issue is capacity. If you use a auto battery they are in the range of 45 to 60 AH or about 500 to 700 watt-hours. That isn't much time when connected to a 4000 Watt inverter, and running a skill saw off of it. You could find yourself needing a jumpstart at the end of the day when it is time to go home.

Last point the two batteries will need to be exact make and models to be series and/or paralleled.



What would you say the max recommended wattage for this kind of set up would be?
There are four modules to the inverter I can take one or two out and make it 3 or 2 kw

[dereckbc]

Exeltech, and the model im not quite sure since its a module assembly it has 4 mx100 power modules, a control card a transfer switch card an alarm card, I know they are pretty expensive, I looked it up when I got them, but I don't remember anymore, I was planning on getting some solar panels to hook them up to the house, but haven't done it yet, maybe this year, hurricane season is upon us.

I was about to say these are a heck of a lot better inverters used in solar PV apps. The stuff they make is pure junk.

If you do use them in a solar PV system you are talking some huge expense to take advantage of these monster inverters like 4 to 8 KW solar array, and if used off-grid and 4000 AH batteries @ 24 VDC is around $50K plus that much more in solar panels. Only problem is I doubt the inverters could be used in grid tied systems because they do not have the capability to sync with the POCO or auto shut-off in the event of power failure. So you could probale only use them in off-grid app.

[wireguru]

id sell them off to a place that buys telecom equipment and use the proceeds to purchase the correct inverter for your application (and you'll probably have a ton of $ left over too)

[dmanda24]

I was about to say these are a heck of a lot better inverters used in solar PV apps. The stuff they make is pure junk.

If you do use them in a solar PV system you are talking some huge expense to take advantage of these monster inverters like 4 to 8 KW solar array, and if used off-grid and 4000 AH batteries @ 24 VDC is around $50K plus that much more in solar panels. Only problem is I doubt the inverters could be used in grid tied systems because they do not have the capability to sync with the POCO or auto shut-off in the event of power failure. So you could probale only use them in off-grid app.

You can connect them to your house grid, since it has an automatic transfer switch, but you cannot use them while the power is on to put power back on the grid and sell power to the POCO since as you said it does not have the avility to sinc with the grid.

[dmanda24]

id sell them off to a place that buys telecom equipment and use the proceeds to purchase the correct inverter for your application (and you'll probably have a ton of $ left over too)

probably the best thing to do, but not sure who would buy used equipment

[mdshunk]

probably the best thing to do, but not sure who would buy used equipmenteBay that crap. There's enough people experimenting with home-brew solar right now, the time is right to sell it on the open market like that. The demand is great right now, is what I'm trying to say.

[LarryFine]

would I still need the DPDT switch? Yep. Need a diagram? :grin:


What would you say the max recommended wattage for this kind of set up would be?
There are four modules to the inverter I can take one or two out and make it 3 or 2 kw That's not necessary. The inverter will only use what it must to produce the current you're trying to get from it.
(This ignores losses and inefficiencies, of course)

If you use 2kw, it'll pull half of the 170a anyway; the extra modules won't change that. I'd rather have them in for starting current, short-term peak demands, and reliability.

There should be no issue with jump-starting at the end of the day because, as Derek said, you should use matching batteries, and they should be independent of the vehicle's electrical system.

Since you can't charge at 12v and use at 24v at the same time anyway, you won't be able to use the inverter while recharging from a vehicle. Why not just make it an independent 24v system with a 24v plug-in charger?

You should definitely use deep-cycle batteries. Nobody says you can only use two, remember. If you find you don't get enough run-time with one pair of batteries, add a second pair, wiring them in parallel-series.

Truck parts and accessory stores have a lot of pre-made battery cabling. I've seen cable assemblies with two, three, and four battery clamps. The wire was larger than anything you'll find at the Pep Boys, NAPA, Auto Zone, or Advance.

[dmanda24]

Since you can't charge at 12v and use at 24v at the same time anyway, you won't be able to use the inverter while recharging from a vehicle. Why not just make it an independent 24v system with a 24v plug-in charger?


got a diagram? j/k what do you mean by a 24V plug-in charger? A DC-DC converter??

[LarryFine]

got a diagram? j/k what do you mean by a 24V plug-in charger? A DC-DC converter??
No, a 24v charger that runs on 120vac. If there's power at a jobsite, charge it up. Otherwise, wait until you get home and plug it in there.

An alternative is to find a 24v alternator with built-in regulator, and find a way to mount and drive it from your engine.

[dereckbc]

Ya know if you really want an inverter for your vehicle, you would be much beeter off just buying a 12 inverter. Then you can just run the vehicle while using the inverter and not have to jury rig a thing.

How much you want for the thing? I got an application for one.

[dmanda24]

make me an offer

http://www.exeltech.com/downloads/mxbrochure.pdf

mine looks like the diagram in page 3 but with only 4 mx1000 modules instead of 5

[wireguru]

make me an offer

http://www.exeltech.com/downloads/mxbrochure.pdf

mine looks like the diagram in page 3 but with only 4 mx1000 modules instead of 5


very nice. id want it if it werent for my excellent chinese source for sinewave inverter with ATS and battery charger :)

[dmanda24]

id sell them off to a place that buys telecom equipment and use the proceeds to purchase the correct inverter for your application (and you'll probably have a ton of $ left over too)

Do you know of a place where I can sell this?

[wireguru]

i know of a guy who deals in surplus cell site equipment, i bought some network gear off him one time. I can try to dig out his contact info, but no guarantees as it was a couple years ago.

[dmanda24]

I appreciate it

[iwire]

A member that is no longer active had a real sweet inverter set up in his truck.

Two extra marine grade batteries with isolators, larger alternator and a device that would automatically start the truck when the voltage dipped to low.

He was a new home electrician and found that this setup was much better then hauling and listening to a gas generator.

If you would like I can probably find his posts, he gave all kinds of info.

[dmanda24]

A member that is no longer active had a real sweet inverter set up in his truck.

Two extra marine grade batteries with isolators, larger alternator and a device that would automatically start the truck when the voltage dipped to low.

He was a new home electrician and found that this setup was much better then hauling and listening to a gas generator.

If you would like I can probably find his posts, he gave all kinds of info.

yeah, I have 4 of these things maybe I could sell 3 and use some of the money to set up the fourth one in the van

[iwire]

Took a bit, it was hurk27 that had done up his van.

He mentioned it in a few threads, if you search using his name you can find them but here is one where he describes what he did. It was more then I remembered.

http://forums.mikeholt.com/showthread.php?p=478010

He was active here as recently as May, he would proably repond to a PM given enough time.

[gar]

080627-1129 EST

While charging batteries in parallel from a car alternator why do you want diode isolation?

The source voltage of the charger while charging is higher than the internal voltage of the battery and therefore you have positive current flow into each battery. Note: the diode will add maybe 1.5 V drop and thus the battery will charge much slower.

When not charging there is no current flow back into the charger because of the diodes in the charger or a cut-out relay. If the batteries are not matched there might be some flow from one battery to the other.

Since switching from parallel to series is likely to be complicated you might consider other alternatives. Also it might not be advisable to use the vehicle battery as one of the batteries. A gas power generator with adequate sound attenuation would be my choice.

Do look at your energy requirements. If you had a 10% duty cycle on 1 HP and assume that at 1000 W, then average consumption is 0.1 KWH. At 24 V that is 4 A average and peaks of 40 A. Two car batteries assuming 70 ampere-hour each and you could run for about 17 hours.

.

[dereckbc]

Bob what ever happened to Wayne? (aka hurk)

[iwire]

080627-1129 EST

While charging batteries in parallel from a car alternator why do you want diode isolation?

In many cases it is so the axillary battery(ies) is / are not discharged by the inverter leaving the original car battery fully charged for starting the vehicle.

[iwire]

Bob what ever happened to Wayne? (aka hurk)

I emailed him about that a while ago. He just found other interests. Namely a women. :smile:

[dereckbc]

I emailed him about that a while ago. He just found other interests. Namely a women. :smile:Nuff said:roll:

[dereckbc]

In many cases it is so the axillary battery(ies) is / are not discharged by the inverter leaving the original car battery fully charged for starting the vehicle.Depends on where you install the diode. If installed between the alternator and the aux battery, it will isolate the vehicle battery from the aux battery system.

However if you install the diodes between the vehicle battery and aux battery, the vehicle battery will supply the inverter and drain it down after the aux battery drains down below the bias threshold of the diode to cause foward conductance.:wink:

[iwire]

Depends on where you install the diode.

Well yes.... :grin:

Wayne's design isolated his ten auxiliaries from his truck battery.

[dereckbc]

Well yes.... :grin:

Wayne's design isolated his ten auxiliaries from his truck battery.Ten batteries? What the heck was he driving: A nuke plant? :grin:

[gar]

080627-1253 EST

bob:

The proposed circuit was to charge the batteries in parallel and use them in series and thus the need for some switching before use of the batteries. The original idea had the disadvantage of running down the vehicle battery plus the switching complexity.

A better idea that was suggested was to use two additional batteries and a 24 V alternator.

True if the batteries are always used with the diodes as routers and the inverter load is only on one battery the circuit is useful. But diodes instead of some other switching means have my previously mentioned voltage drop problem. Raising the voltage of the regulator to compensate would be useful if you could easily do this.

A quick check on my car. Before starting the battery voltage was 12.53 V shortly after starting 14.13. Subtract 1.5 V and that would lower the charging voltage to 12.63. Is 1.5 realistic? Maybe not. For a 70 A 70HF40 the typical drop is about 1 V at 70 A and that is also 70 watts to dissipate. This same diode at 10 A is about 0.9 V. It is still a substantial loss of charging voltage to assume a 1 V drop. Then we have in my case 13.13 as the charging voltage.

Using a Schottky diode will lower the drop.

.

[iwire]

Ten batteries? What the heck was he driving: A nuke plant? :grin:

I was pretty surprised as well. That is some serious run time for a 1/2" drill.

Right now I have a 600 watt Walmart special that does run my chargers just fine even with it's anything but a sine wave output. :grin:

[iwire]

080627-1253 EST

bob:

The proposed circuit was to charge the batteries in parallel and use them in series and thus the need for some switching before use of the batteries. The original idea had the disadvantage of running down the vehicle battery plus the switching complexity.

0U812-5150 EST

Forget it, sorry I even suggested a possible reason. :roll:

[gar]

080627-1349 EST

dereckbc:

Bob is correct that two diodes can prevent running down the vehicle battery. Basically the anodes of the two diodes are connected to the + output of the alternator, and one cathode goes to the vehicle battery, and the other to the inverter battery. When the engine is off these diodes are back to back and a dead inverter battery puts no load on the vehicle battery.

.

[gar]

080627-1416 EST

bob:

Your response on the reason was valid for the normal way diodes are used with an auxillary battery. My original comment was because I did not think the original suggestion of the diodes was useful for the intended application.

Where diodes are a useful solution for an application except for the diode drop I think a different approach might be better. This might be a relay that connects the auxillary battery to the charger when the charger was charging. Probably might include some electronics. This would monitor charging current from the charger and when this was positive it would close the relay to the auxilary battery.

.

[dmanda24]

I do not think for this particular application there is a need for diodes. because the inverter cannot be used while the batteries are charging therefore all is really needed is a switch to disconnect the two inverter deep cycle batteries from the car system when the batteries are in series feeding the inverter. I think.

[dmanda24]

for those of you guys that are familiar with these kind of systems, what would you say is a fair price for the seller as well as the buyer for a unit like this, keep in mind they are used but in good condition.

[dereckbc]

Going price for new is about a dollar a watt.