12 volt to 110 ac - Is My Thinking All Wrong?

[Makin__Do]

OK , I'll admit to being no expert when it comes to electrical matters, so put this question under the topic "will this really work?". I'm getting two new Lifeline 6 volt GPL-4CT AGM batteries. Since they cost $600 I'd really like to keep them "healthy". My battery isolator puts out 15.5 volts at idle, which always caused my wet cell batteries to be on boil most of the time. Now, I don't want to over charge the AGMs and the way I understand matters 15.5 volts is way too much of a constant charge. The only item drawing power going down the road will be my Engel DC fridge, which isn't drawing power all the time. So here's the real question: can I connect the isolator output to a 400 watt inverter and run a Progressive Dynamics 9245 on 110 ac from the converter and let it manage the batteries just like it would be doing if I were hooked up to shore power? Sounds like a plan, but would I just end up with toast?

[MEXICOWANDERER]

harley-dave wrote:

MEXICOWANDERER wrote:
Something is "King-Size" screwball here.

Rectifiers can fail OPEN CIRCUIT. No electronic connection. Just like taking a wire off. No power.

Rectifiers can fail SHORTED. No voltage drop. Just like hooking up a jumper wire bypassing the rectifier.

If the house rectifier shorts, the alternator could care less it's gonna continue to send voltage that's one volt too high to the center stud of the isolator. The chassis gets "corrected" voltage.

The other rectifier however is no longer a rectifier. Alternator voltage is sent directly to the house batteries. And guess what? It's one volt too high.

At this point if it fails 'shorted' your main concern should be the alternator is sending AC power to the battery/circuit, not DC anymore. It will go bad very fast in this scenario.

Dave

When voltage departs any alternator through a FULL WAVE BRIDGE RECTIFIER, 6 working "diodes" like all alternators, the voltage is DIRECT CURRENT. DC NOT AC

The rectifier type isolator puts a SECOND SET of DIODES behind the first. Two rectifiers in SERIES. So unless BOTH the alternator rectifier AND AND AND AND the isolator rectifier fails, you are working with pure DC current. Perhaps you mistake a remote rectifier package in which three ALTERNATING CURRENT A.C. is sent to remote rectifiers.

The shorted isolator rectifier scenario is COMMON and it has cost RV owners a lot of money.

(Know-It-All-RV-Owner)

"Howcum my RV battery boiled and not the vehicle battery? Itza crummy RV battery - you can't fool me" He's right, it's tough to further fool a fool.

[3_tons]

Makin' Do wrote:
OP here. Thanks for your input, some from those that know as little as I do and those that do know what they are talking about.
I checked the voltage output at the engine battery and the connection point where the house battery is located just to make sure I read the numbers right. At the engine battery voltage was 14.4 steady output (same as the digital voltmeter on the dash) and at the house battery it is indeed 15.4 to 15.8, bit of a fluctuation. Have a new isolator in the shop so I'll swap them over the weekend when the weather warms a little and see if there is difference at the house battery.
400 watt inverter is indeed out of the question. I do have a new, never out of the box Duracell 1500 watt inverter (modified sine) that I bought six or seven years ago that I forgot I had (wife had to remind me). I think the only reason I bought it was the price, $63 on Amazon. Never had a real plan for it.
Read the owners manual, all 67 pages, and on page 67 it said "do not hook up the invert to a battery isolator". So much for a plan. Then again, Mr Wizard said it just might be possible. Maybe I could go with solar panels as suggested.

Sounds like a two part question

a) Isolator voltage is too high - you're tackling that one...

b) An isolator cannot supply sufficient 'current' to run an inverter, thus, a good sized inverter should be connected directly to the house battery using properly sized and length cables. Undersized cables will cause a bottleneck, causing low voltage alarms.

[Sam_Spade]

Makin' Do wrote:
and at the house battery it is indeed 15.4 to 15.8, bit of a fluctuation.
Maybe I could go with solar panels as suggested.

As I mentioned before, you NEED to find out what is making that voltage too high and get it fixed. 16.0 is the upper limit where things might start blowing.

Ignore this advice at your own peril.

[MrWizard]

Have you checked the voltage at or near he alternator
Something is really screwy with the wiring in your system

The voltage description, sounds like the alternator is connected to the house batteries, but the voltage sense wire is on the engine battery
And the isolator is Not installed correctly

[time2roll]

http://www.allbatterysalesandservice.com/graphics/Marine-Isolators.pdf

[Makin__Do]

Too be sure, 15.8 is way too much. I'll finish replacing the current isolator on Sunday with a Sure Power model 702. Hope this corrects the problem.

[time2roll]

If the chassis is 14.4 and the house is 15.8 I believe there is something wrong with the isolator, how it is connected or the alternator sense wire is in the wrong position.
Has the isolator ever been replaced? Other custom wiring work by prior owner?

Post the isolator model number and a picture of all the wires connected for best answers.

House at 15.8 is wrong in every way.

[pianotuna]

If you design the solar system properly it may nearly eliminate running a generator, except for running a roof air conditioner.

[Makin__Do]

OP here. Thanks for your input, some from those that know as little as I do and those that do know what they are talking about.
I checked the voltage output at the engine battery and the connection point where the house battery is located just to make sure I read the numbers right. At the engine battery voltage was 14.4 steady output (same as the digital voltmeter on the dash) and at the house battery it is indeed 15.4 to 15.8, bit of a fluctuation. Have a new isolator in the shop so I'll swap them over the weekend when the weather warms a little and see if there is difference at the house battery.
400 watt inverter is indeed out of the question. I do have a new, never out of the box Duracell 1500 watt inverter (modified sine) that I bought six or seven years ago that I forgot I had (wife had to remind me). I think the only reason I bought it was the price, $63 on Amazon. Never had a real plan for it.
Read the owners manual, all 67 pages, and on page 67 it said "do not hook up the invert to a battery isolator". So much for a plan. Then again, Mr Wizard said it just might be possible. Maybe I could go with solar panels as suggested.

[MrWizard]

Yes you can do this
If the inverter doesn't shut down from a over voltage alarm
And the wave form of the inverter is OK with the charger

[Happy_Prospecto]

Makin' Do wrote:
OK , I'll admit to being no expert when it comes to electrical matters, so put this question under the topic "will this really work?"....... So here's the real question: can I connect the isolator output to a 400 watt inverter and run a Progressive Dynamics 9245 on 110 ac from the converter and let it manage the batteries just like it would be doing if I were hooked up to shore power?

Sure, go ahead what can possibly go wrong.

[RJsfishin]

Quote:
12 volt to 110 ac - Is My Thinking All Wrong?
-----------------------------------------------
Yes ! Your thinking is just about as ineffiecent, and unnecessary as it can get. Like said, fix the problem, if you even have one.

[harley-dave]

MEXICOWANDERER wrote:
Something is "King-Size" screwball here.

Rectifiers can fail OPEN CIRCUIT. No electronic connection. Just like taking a wire off. No power.

Rectifiers can fail SHORTED. No voltage drop. Just like hooking up a jumper wire bypassing the rectifier.

If the house rectifier shorts, the alternator could care less it's gonna continue to send voltage that's one volt too high to the center stud of the isolator. The chassis gets "corrected" voltage.

The other rectifier however is no longer a rectifier. Alternator voltage is sent directly to the house batteries. And guess what? It's one volt too high.

At this point if it fails 'shorted' your main concern should be the alternator is sending AC power to the battery/circuit, not DC anymore. It will go bad very fast in this scenario.

Dave

[wa8yxm]

The easiest way to reduce voltage is to pass the power through a high current diode.. You can get Diode Isolators at most Auto Parts places and RV stores, they are fairly large (Finned, and have 3 or 4 or more bolts (3 big minimum) you will use the center BIG bolt (IN) and one of the out bolts (or y0ou can parallel both of them, does not matter) each one will cause a slightl drop in voltage.

What I can not tell you, since it depends on the diode, is the voltage drop So measure.