24 V DC to AC Inverter

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iwire

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A member that is no longer active had a real sweet inverter set up in his truck.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

Senior Member
iwire said:
A member that is no longer active had a real sweet inverter set up in his truck.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
 

gar

Senior Member
Location
Ann Arbor, Michigan
Occupation
EE
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.

.
 

iwire

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Location
Massachusetts
gar said:
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.
 

dereckbc

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Plano, TX
iwire said:
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:
 
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gar

Senior Member
Location
Ann Arbor, Michigan
Occupation
EE
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

Moderator
Staff member
Location
Massachusetts
dereckbc said:
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

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Staff member
Location
Massachusetts
gar said:
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

Senior Member
Location
Ann Arbor, Michigan
Occupation
EE
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

Senior Member
Location
Ann Arbor, Michigan
Occupation
EE
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

Senior Member
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

Senior Member
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.
 
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