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]

Something is "King-Size" screwball here.

The highest alternator voltage regulator factory setting I know of was the Delco 15SI 1116405 of the late seventies and early 1980's. 15.0 volts. Delco's nightmare "New Coca Cola" grade attempt to make GM cars exclusive to using the Delcotron calcium/calcium sealed battery. They cost half again as much as a good standard battery. The battery design was worthless and the regulator voltage ranked right up there with GM's bright idea to use copper plated aluminum battery cables.

Because of higher underhood temperatures, OEM has been trending voltage regulator settings in the 13's for 40-50c battery temperatures.

However, a rectifier-type isolator is capable of malfunctioning more ways than Carter has Little Liver Pills.

Try this on for size...

Here we have a correctly connected 3-terminal finned type rectifier isolator. One side is connected to the vehicle engine chassis, while the second rectifier feeds the "house" batteries.

The voltage regulator of course, senses voltage from the vehicle chassis side of the isolator.

But WAIT! All is not well in paradise! Yes the rectifiers drop voltage nearly a full volt, and yes the alternator output stud to isolator center stud will read a full volt higher because after-all those two rectifiers in the isolator will reduce voltage one full volt on each side, meaning both sides - the vehicle chassis and the house side. Compensated voltage yeah-yeah-yeah!

Until one of the isolator rectifiers decides to fail.

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.

This is not a diagnosis of what you wrote - it's merely a suggestion as to how an alternator rectifier type charge divider system can malfunction.

15-volts will kill an AGM battery every bit as fast as it will a flooded battery. A compromise voltage from an alternator would be 13.6 volts. Problems arise when a search is conducted for a DC to DC voltage "adjuster" that can withstand amperage that is near to the potential of the alternator.

Because of the extremely high charge acceptance (lower internal resistance) of the AGM battery, they are less cranky about voltage than a flooded battery when recharging, and fast recharging is a requirement.

[Sam_Spade]

What exactly is a battery "isolator" and why is it putting out such a high voltage ? I think you should fix that first.....as it might cause damage to other things connected to it also.

If this really is the output of the alternator as others have suggested, and it is ALWAYS at that voltage, then the regulator part of the alternator has failed and it NEEDS to be fixed. The upper design limit for most 12 V equipment is 16.0 volts and you are dangerously close.

[RoyB]

Futher the 1000WATT POWER INVERTER will want to draw around 80 PLUS DC AMPS to run your connected PD9245 converter/charger unit. My PD9260C 60AMP Converter/charger pulls right at 1000WATTS plugged into 120VAC... I would have to check the specs on how many input watts the PD9245 unit will draw...

That is going to be a pretty heavy load for your truck alternator... Not good...

Worse case problem it may blow your truck alternator... Not good...

Secondary case problem it may only run for about 15 minutes before discharging your truck start battery and shutting down the Power Inverter... Not good...

All Power Inverters are power hungry on the 12VDC side...

The PD9245 converter/charger unit expected to run at least three hours each time it is used to recharge your battery bank from a 50% charge state to its 90% charge state. It will take around 12 hours to fully charge your battery bank to a full 100% charge. Each battery in the battery bank will want to draw around 17-20AMPS DC current when first hit with 14.4VDC smart charging mode. Then it will slowly taper back as the batteries are taking on charge.

This is all according to Progressive Dynamics on how long it takes to charge deep cycle batteries starting with 50% charge state depleted batteries...

The PD9245 Converter/charger should be connected to 120VAC Shore Power or run by a 2KW generator for those long charge times...

Food for thought

Just my thinking
Roy Ken

[pianotuna]

9245 is nominally about 700 watts with a power factor of 0.7. 1000 watt pure sine wave inverter would be my choice.

[time2roll]

15.5 volts is from the alternator? Isolator is not producing power.
While 15.5 might be normal initially it should drop to 14.5 or less within 20 minutes. With the longish wire run your AGM may never see 15.5 volts. Otherwise I might be looking to verify the alternator is operating correctly.

Really need a 1000 watt inverter to power a 9245.

[2oldman]

I suppose you could.. do you know the amperage of the 15.5 volts?

Many of us find roof-mounted solar to be a good idea not only for camping but for going down the road.