AGM charge rate

[Mike in GA]

My literature from Lifeline says the charge rate for the new batteries should be on bulk between 28.4 and 28.8 volts. On float they stipulate between 26.4 and 26.8
The voltage  put out by the bus alternator today after a one hour run was 27.8 volts so I guess the screw on the voltage regulator needs adjusting.
Question - do I choose to raise the alternator output to the required bulk rate, or lower it to the float rate?
I usually only hit the batteries going down the road for a couple hours max, so my guess is the higher rate.
Will either change affect the flooded wet cell coach/start batts?
Thanks in advance for the shared wisdom.
Mike in GA

[Oonrahnjay]

Mike, I haven't looked at this closely but my first instinct is to add a separate alternator for the "house batteries" and set that for AGM.  You'd have redundancy and a source of charge that you can set to the exact needed voltage.
But that may be over-thinking.

[Nick Badame Refrig/ACC]

Hi Mike,


You could easily install a switch on the dash along with a volt meter for the house bank and simply
flip the switch off when you think the bank is where you need it. This will allow the start batteries
to continue to charge normally from the engine.

Another option would be to install AGM's for your start bank and set the alternator accordingly.

Good Luck
Nick-

[luvrbus]

Check out the Balmar systems i seem to remember they had a system for that problem

[bevans6]

I set my alternator to suit the start batteries and I set the inverter to suit the house batteries.  That high charge rate for the AGM's will damage the start batteries long term.  The lower voltage for the start batteries won't damage the AGM's, so that's where I go.

Brian

[Tony LEE]

We don't have the full picture of your system. Is the engine alternator the sole charging source for your house batteries or do you have a decent solar system to top them off.

Realistically it is rarely possible to fully-charge house batteries from the engine using a simple connection because the alternator characteristics are set so as to not overcharge the start batteries during continuous running (which is what passenger buses are built for)

Also - there are two parameters involved in battery charging. There is charge rate in Amps, and end of bulk charge voltage (and of course float voltage as well) and you don't have much if any control of either of  these with a simple alternator system. If you have a shunt and ammeter and voltmeter installed in your house battery circuit you would be able to know exactly what you  are achieving. Voltage by itself isn't much help.

On my MCI, after a few days camping without decent solar input, the alternator puts about 160 amps into the 520Ah battery and this tapers off over the first 90 minutes to about 50 amps at which point the battery is still only less than 50% charged so the current has never been high enough to cause problems with the AGM battery.  I generally isolate the alternator charging not long after that and let the 600W of solar finish the job.

[digesterman]

Tony not many have solar systems on their buses, very few I think. My engine charging system keeps my house batteries full when on road, thought most did.

[Branderson]

So last week, I was messing with my fan vent in the bathroom and if you recall, I was having air line issues to my front airbags.  So I had my gen running to get power to the fan and I was doing this while on lunch break.  So I turn off gen and go back to work.  I forgot to turn off my house battery power and inverter.  It wasn't until a few days later that I remembered and drove back and sure enough my AGM 2 batteries were near dead.  I just bought those last year so I was looking at a $700 stupid mistake.

Once I got the air line fixed, I got it back to my house so I could put my battery charger on them.  It took a good 4 days for my charger to get one of the batteries to 100%.  I'm currently charging the 2nd one now.

From what I read, AGM recharging is a slow charge rate but I'm just glad they are taking a charge.

I know most in here are vets in the bus world but please tell me I'm not the only one that has been a dummy and left something on before?  I've basically drained every battery except for the gen battery and I'm including the TOAD.

[bevans6]

I left the vanner connected and it discharged my batteries to 1.5 volts.  They came back, though.  Rolls battery suggests that a 12V AGM should be charged at around 14.8 volts and 0.2 - 0.3 times the 20hr AH rating in amps.  So a 200 AH battery would be charged at 14.8 volts and 40 - 60 amps.  http://support.rollsbattery.com/support/solutions/articles/4345-agm-charging

Slower is fine.  AGM's are designed for deep discharge (to 20% SOC) and have a reputation for recovering from bad things.  If their gas relief valves have popped, the battery is usually considered done for.

[DoubleEagle]

please tell me I'm not the only one that has been a dummy and left something on before?  I've basically drained every battery except for the gen battery and I'm including the TOAD.

You are definitely not the only one, but after you ruin a few, the memory gets better. My main problem has been trickle chargers that start draining the battery if the power goes off (and you have to remember to disconnect them when there is a power outage). 

[buswarrior]

Leaving things turned on, is like leaving the house without your pants on...

You had to be taught modesty, it took a lot of effort by our parents...
You have to teach yourself that there is ALWAYS a shut down process that MUST be followed, EVERY TIME.

Not a hobby for those lacking in self discipline?

Or, spend a lot of bu$ buck$ repeating purchases that you already made...

Happy coaching!
Buswarrior

[Branderson]

I think it's safe to say that this mistake should scare me straight and to take my time when shutting down.  The ironic thing is the past month, I've been trying to make sure everything is right for my first dry camp at Talladega races.

The one good thing about this is if it didn't happen, I would have had that air issue as I was getting ready to leave for the races which would have given me little time to fix.  That being said, I don't want to get in the habit of draining these batteries b/c I'm told that they are great batteries but don't like to be drained all the way down. 

[windtrader]

There are cutoff devices that will disconnect when voltage drops below X. Plus, you should be able to nurse the batteries back to life since the duration of total discharge is not long, not like being discharged for months or years.



BW - "Not a hobby for those lacking in self discipline?"


Was that supposed to be a statement rather than a question?
In a perfect world, a the novice bus conversion nuts would have sufficient extra time/energy to devote to practicing bus operator skills. The reality is many do not have even enough time to just take a journey much less extra time to practice such that there is "self discipline" imprinted in the rote memory cells in our brains.

[buswarrior]

You've read enough forums and social media sites.

The same people murdering batteries over and over, spending a lot of money unnecessarily, and if enough of them keep typing, it appears to be normal for the new busnut?

Will not those lacking in self discipline be spending a lot of money that could be spent on other things?

Happy coaching!
Buswarrior

[Branderson]

I spent 23 years in the army buswarrior so blanketly stating I lack self discipline is bullsh*t.  If you think that anyone that makes a mistake or overlooked something falls into that category then I would like to know how it feels to be so perfect in life. Sitting pretty high on your horse judging like that.