Forester alternator charged 15amps in 5 hours?

[Sagecoachdriver]

On our trip home from Yosemite today, I noted the ahr draw totaled 29amps on my Xantrex battery monitor. I've been charging the house batteries with solar and generator every day. It's been pretty accurate over the past years. We drove 295 miles in 5 hours 30 minutes. When we got home, I checked it and it was still down 15 amps.
In our 2004 Winnebago Minnie, it would have had the batteries fully charged. The engine battery should have had very little parasitic drain as the radio draws off the house batteries. Also, the normal house battery draw from fridge etc. is .9-1.2 amps.
Why isn't the alternator doing a better job?

[ScottBrownstein]

What is the voltage on the house batteries when the engine is running? I assume that you are referring to the status of your house batteries on the Xantrex. When you start the house bank should come up to something like 14 volts.

[Sagecoachdriver]

Checked the Battery monitor this morning and it shows +0.4 amps Total and it's on topping off mode with zero amps going in and 13.8 volts. I don't recall what the volts were at the batteries with the engine start up upon leaving for home.

[ScottBrownstein]

Originally Posted by Sagecoachdriver

Checked the Battery monitor this morning and it shows +0.4 amps Total and it's on topping off mode with zero amps going in and 13.8 volts. I don't recall what the volts were at the batteries with the engine start up upon leaving for home.

That makes sense as the converter has dropped out of boost mode and is carefully inching the batteries up to 100%. It will eventually drop lower. The reason that I ask is that if the alternator is feeding the house bank through the BCC isolation solenoid, then the battery voltage should be something like 14 to 14.5 when the engine is running allowing the alternator to charge the house bank.

Now I don't know if your coach is set up that way, but most are. The isolation solenoid is a known failure part and might not be making good contact and making it difficult for the alternator to drive significant current into the house bank...hence your long drive with little to show for it.

[Herk7769]

Alternators are terrible deep cycle battery chargers.

They are designed to charge the starting battery which requires FAR less charging after a discharge. In addition, once the starting battery is full, the alternator drops into float and will only output what the truck needs to keep running and about an amp of trickle charge to the battery(s).

Read this article for a more complete explanation.

[B and B]

What Herk said.

Also the resistance of the charge lead from the alternator to house batter is greater than the starting battery. If the starting battery is fine the house batter will never get a full charge. Many years ago in order to fix this my father added 2 diodes in series with the charge lead to the starting battery to fool the alternator to charge the trailer battery more. The diodes provided a voltage drop of 1.4 volts to the starting battery and the trailer batteries were fully charged. Also ran 6 AWG wires to the 7 pin to lesson loss.

[ScottBrownstein]

Originally Posted by Herk7769

Alternators are terrible deep cycle battery chargers....

Herk, I agree, but none of these damn chargers will not go above 14 or 14.5 volts and for deep cycle batteries, that is just not enough. Trojan recommends 15! The only chargers that I have found are smart Solar Charge Controllers, like Bogart's SC-2030. It will go up beyond 15 if so instructed, and solar panels can supply that much voltage.

The problem with converters is that they simply top out at 14.5 and won't go any higher. As the article indicates, if you don't go above 14 or 14.5, a 75% charged battery bank will push back hard enough to drop the current to 5 amps or so and at that current, it's along way to 100%.

I have discussed this with Bogart and also the possibility of using a 110 volt to DC power supply at 18 volts to replace my converter and get the same smarts when charging from AC as well as from solar. They agree that is doable, but I need to find a 30 amp power supply that will put up with PWM.

But only 15 amp hours in almost 6 hours is on the low side.

[camaraderie]

Originally Posted by ScottBrownstein

Herk, I agree, but none of these damn chargers will not go above 14 or 14.5 volts and for deep cycle batteries, that is just not enough. Trojan recommends 15!

Please advise where you are getting 15 from ...Trojan recommends14.8 bulk and 13.2 float.
Battery Maintenance | Trojan Battery Company

[Herk7769]

Originally Posted by camaraderie

Please advise where you are getting 15 from ...Trojan recommends14.8 bulk and 13.2 float.
Battery Maintenance | Trojan Battery Company

It would appear he is talking about the "Equalization" voltage (Stage 4 on a 4 stage charger). This is not (as you are aware), a steady state stage. A 4 stage charger pulses in and out of stage 4 (back to FLOAT) to prevent the destruction of the battery from overcharging.

[camaraderie]

Originally Posted by Herk7769

It would appear he is talking about the "Equalization" voltage (Stage 4 on a 4 stage charger). This is not (as you are aware), a steady state stage. A 4 stage charger pulses in and out of stage 4 (back to FLOAT) to prevent the destruction of the battery from overcharging.

Actually I think he is talking about bulk requirements Herk...but will let him clarify.
FYI Some 4 stage chargers ...jump to EQ stage and back as you suggest, others are timed to come on 7 days (Iota) after being on undisturbed FLOAT, others are a manual choice the owner may engage at will (sometimes augmented by temperature sensor control. (Xantrex).
The small pulse type "trickle charger desulphators" are ineffective at desulphating but do effectively put on a maintenence charge.

[Herk7769]

Originally Posted by camaraderie

Actually I think he is talking about bulk requirements Herk...but will let him clarify.
FYI Some 4 stage chargers ...jump to EQ stage and back as you suggest, others are timed to come on 7 days (Iota) after being on undisturbed FLOAT, others are a manual choice the owner may engage at will (sometimes augmented by temperature sensor control. (Xantrex).
The small pulse type "trickle charger desulphators" are ineffective at desulphating but do effectively put on a maintenence charge.

I was just making the point that "charging" at 15 volts is "bad" for batteries.
Using 15 volts to desulphate/equalize is not "charging".

Thanks for letting me know that some don't pulse but are designed with internal timers (some with manual overrides). I can't believe using that voltage to routinely charge them won't damage the batteries.

[camaraderie]

Yep....understood that..and we agree. The big danger of too much voltage in increased battery temps warping the plates and boil off exposing them. If I were gonna apply 15+ volts unattended...I'd sure have a temp sensor shut down circuit so the batt wouldn't be allowed to get over 120F .

[Herk7769]

So here is a way to charge the trailer battery from the alternator without the danger of destroying either the starting battery or the trailer battery.

ZRD - Duocharge

Something to think about for sure ...

[ScottBrownstein]

Originally Posted by camaraderie

Please advise where you are getting 15 from ...Trojan recommends14.8 bulk and 13.2 float.
Battery Maintenance | Trojan Battery Company

Fine...14.8 at 70 degrees...not exactly 15, but not 14 either and at least my 70 amp converter does not have remote sense, thus 14.5 at the converter, at least 14.3 or less at the batteries.

[WolfWhistle]

What SB is saying is correct. However, with temperature compensation Trojan needs 15v if its cold enough. I think Interstate says 15 volts without regards for colder temps. The point is most converter / chargers barely charge. A full resting flooded 6 cell battery reads about 12.7 volts, one that is dead is 11.8, but better not use one below 12.1 if you want them to last. If you really want to know if a battery is charged use a hydrometer... voltages is a fickle thing. So, back to voltages... from used up to full is a difference of only .6 of a volt. Everyone that cares about batteries and battery usage needs a monitor such as the TM2030, IMO. Many RVs have idiot lights that show when you are fulling charged or points in between. Most of them are very optimistic.
WW

[ScottBrownstein]

Originally Posted by WolfWhistle

...The point is most converter / chargers barely charge...

Couldn't agree more and couldn't have said it better. Everybody is babying these flooded cell batteries and since we have smart chargers there is not reason for converter to stop at a mere 14.5 bulk voltage, especially since it is at the converter output and not on the batteries! Welding cable...please.#4 should be plenty but modern RVs put the converter a long way away from the batteries, in my case 22 feet and the converters never really get to a full charge unless you stay plugged in for 3 or 4 days.

The Bogart SC-2030 runs a much higher boost charge and actually does overcharge based on what the last discharge cycle took out. It has remote sensing and temperature compensation. Frankly I have asked Ralph at Bogart if I can just use a 30 amp 18 volt supply to let the 2030 do it all and dump my converter. Then I would have a smart solar and shore power charger that did it right and the 30 amps would be wonderful compared to what my PD 70 amp unit generally puts out.

In the past, RV's seldom had inverters and all of the electronics that they have today. Not unusual for a coach to have 4 batteries and a residential reefer. Generator charge is fine but my PD Converter wastes the opportunity to push a lot of charge when the genny is running even if I force it into boost with the pendant.

Strange that all of a sudden Progressive Dynamics started to offer a converter with 14.8 volt output? I think they are getting the picture. I have also seen a lot of data that suggests that PD converters do not like the waveform coming from Onan generators as well. Either way, I am logging oll of the data from my Trimetric to an SD card so on my next trip I will really know what happened. That should be interesting.