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Old 04-08-2016, 02:42 AM   #1
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Forester alternator charged 15amps in 5 hours?

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?
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Old 04-08-2016, 06:03 AM   #2
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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.
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Old 04-08-2016, 04:40 PM   #3
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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.
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Old 04-08-2016, 05:01 PM   #4
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Originally Posted by Sagecoachdriver View Post
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.
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Old 04-09-2016, 08:17 AM   #5
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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.
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File Type: pdf Automobile Alternators as Chargers.pdf (805.9 KB, 24 views)
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Old 04-09-2016, 08:32 AM   #6
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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.
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Old 04-09-2016, 08:32 AM   #7
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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.
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Old 04-09-2016, 08:50 AM   #8
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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
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Old 04-09-2016, 09:02 AM   #9
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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.
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Old 04-09-2016, 12:22 PM   #10
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Quote:
Originally Posted by Herk7769 View Post
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.
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