Deep Cycle Battery Charging From Alternator

Renogy's DC to DC battery charger $129

I would charge your AGM after a trip with your 3-stage converter 24 hours then disconnect the battery for the daily driving. Reconnect when packing for the next trip. I recommend Lifeline brand battery and Progressive Dynamics converter.

time2roll wrote:
I would charge your AGM after a trip with your 3-stage converter 24 hours then disconnect the battery for the daily driving. Reconnect when packing for the next trip. I recommend Lifeline brand battery and Progressive Dynamics converter.

Problem there is you can't meet the Lifeline charging specs with a PD converter. You can pick the right amps size to meet the 20% charging rate, but need adjustable voltage to meet the spec voltages and then adjust those voltages for temperature compensation.

The PD 14.4 or 14.8 fixed voltage will nearly always be wrong, and never right for the recommended "conditioning" charge of 15.5 as adjusted (could be 16v eg) when the battery is used for deep cycling.

IMO, when you can't meet the charging specs for AGMs (also need an ammeter to see when you are at the 0.5a/100AH point) you are way better off with a Flooded , not sealed, battery. You can tell where you are at with an hydrometer and can add water as needed.

Only trouble is where you can't get at the battery to do the work without taking the whole RV apart or hauling 70 pound batteries out from trays so you can see down the cells. AGMs are desired for that, but now you are back in the soup for how to look after them without an adjustable voltage charger and an ammeter.

http://lifelinebatteries.com/wp-content/uploads/2015/12/6-0101-Rev-E-Lifeline-Technical-Manual.pdf

Lifeline charging spec 14.4 volts, PD charging 14.4 volts.
How close does it need to be?

Conditioning only recommended if there seems to be lost capacity.

Your problem is that you're drawing down the batteries too much. Rule of thumb for any lead acid battery is to never discharge below 50%. Your fridges alone need 120 amp hours a day. I would imagine your actual use is closer to 200-220 amp hours per day. Realistically you need 400+ amp hours of battery capacity and at least 400 watts of solar to replenish that or to be able to run a generator 5+ hours a day.

I would install at least 4, and perhaps 6, GC2 style golf cart batteries. Four will get you 215x2= 430 amp hours which gets you at approximately 50% discharge per day. There are AGMs available if you desire, they cost more. I haven't had to put any water in my batteries at all in the last 5 months, but you do need to be able to check them. 400 watts of solar will replenish about 25 amp hours per hour of full sun (assuming 80% of the 400 watt capability), which will require 8-9 hours of sun per day to replenish your daily use. If you think you're going somewhere where you'll have cloudy days, consider more battery capacity.

You should plan to have enough capacity from your solar and batteries to cover your use. That way whatever the alternator or inverter gives is just a bonus.

Note that solar isn't the only way to accomplish this but ultimately, your problem is that your storage tanks (batteries) are too small for what you're trying to do. That is why they had short life and I bet pitiful performance. Honestly I'm surprised they lasted as long as they did.

BFL13 wrote:

...
The PD 14.4 or 14.8 fixed voltage will nearly always be wrong, and never right for the recommended "conditioning" charge of 15.5 as adjusted (could be 16v eg) when the battery is used for deep cycling.
...

Most converter/chargers, like PD and IOTA, that are so popular as replacements for the WFCO do not charge AGMs correctly. The WFCO is the worst because it NEVER reaches proper ABS Voltages.

Why is an adjustable, temperature compensating charger important?

HTH;
John

time2roll wrote:
Lifeline charging spec 14.4 volts, PD charging 14.4 volts.
How close does it need to be?

Conditioning only recommended if there seems to be lost capacity.

In the Lifeline specs (linked above) see table 5.1 where the spec Vabs 14.3v at 77F becomes 14.72 at 50F and 14.9 at 40F

Read para 5.5 farther along where they discuss "routine conditioning". This would be needed for many/most RVing scenarios. Every 2 to 4 weeks note. They have a temp comp table for that too adjusting from 15.5 at 77F--voltages higher when cooler.

Mex can say "how close does it need to be?" but LY has confirmed his AGM loses capacity if he does not follow these kind of instructions. Lifeline is quite serious about what they say there.

IMO the point is the Lifeline AGM especially, but other brands too are expensive compared with flooded batts. So if you can't meet the AGM charging specs, it is going to cost you money.

Most RVs are simply not equipped to meet proper battery charging specs, AGM or Flooded, and most RVers would not have the time or desire to bother with it all even if they had the equipment. Easier to keep buying new batteries.

Plenty of reports of Lifeline lasting 10+ years without all the charging drama.

Originally my point was to get the house battery charged and out of play while doing the day to day commute. I believe the repeated cycling and poor charging is the primary reason for short battery life.

Maybe OP could do a recondition cycle on the existing batteries and get another season out of them.

atp20 wrote:
Hello,

May I ask for advice regarding charging deep cycle batteries from the alternator? I have read older threads, and understand opinions vary.

The previous two 100Ah deep cycle AGM coach batteries each failed in well under two years of intermittent use in my 2003 Sprinter Class B.

Would non-AGM deep cycle batteries last longer? AGMs have been said to be sensitive to overcharging. Any battery recommendations? Maintenance-free would be preferred because of awkward battery access.

Do I need to look into some sort of smart charger, alternator-to-battery charger, or inverter/charger setup? I'd like to keep things simple.

Would installing a second coach battery affect the situation?

The RV is used as a daily driver and for long distance trips, boondocking mostly. When traveling, the principal load consists of two refrigerators, drawing 2.5A each when active, plus a high power blender that draws about 95A (12v) through a 2kw inverter for two minutes a day. The coach battery is located under the rear floor, about 20' from the alternator. Not sure of the connecting wire size, which runs through an isolator and 50A breaker. The 120A(?) alternator charges at 14.4 volts when the battery is full.

Thank you. Any advice would be appreciated.

Jerry S
2003 Freightliner Sprinter Class B
S Florida

Yes ... it is possible to properly, and for good long term service, keep charged RV coach batteries from the main engine's alternator. We have been doing it for 13 years with our Class C's Ford E450 stock 130 amp alternator. The Class C is now on only it's 2nd set of two 12 volt AGM deep cycle batteries. I replaced the first set of AGM coach batteries after about 8 years "just-in-case" - as they were still functioning well after the 8 years.

However, there are some things to be aware of, such as:

1. Is the wiring between the alternator and coach battery bank of large enough gauge size so as to minimize voltage drop along the wire's length while the charging is going on?

2. Is the alternator large enough capacity such that it's not getting stressed too much when the coach batteries are down a bit when starting to charge?

3. Do you have a permanently mounted voltmeter that shows alternator output voltage at all times, and a permanently mounted voltmeter that shows the voltage on the coach batteries's terminals at all times?

4. Do you have a permanently mounted ammeter that shows the current flowing from the alternator into the coach batteries at all times?

5. Is the alternator mounted under the hood such that it gets pretty much a solid and direct blast of air continuously from the radiator fan?

6. Is the alternator connected to the coach battery bank with a heavy duty interconnect solenoid - with silver coated contacts - so that the interconnect solenoid's contacts don't corrode much, or at all ... and hence not reduce the actual voltage that is on the batteries's terminals versus what voltage the alternator is holding on it's terminals?

Our small Class C motorhome's setup meets the above criteria. Our coach battery bank consists of two Group 31 12 volt deep cycle AGM batteries of 115 amp hours each - hooked together in a balanced parallel configuration - for a total capacity of 230 amp hours. When we're camped without hookups and our battery bank is down around 50%, the Ford's V10 alternator can dump up to 70 amps at engine idle into the coach battery bank (according to the ammeter). I sometimes charge this way for about an hour before firing up one of the RV's generators to finish the charging ... or use only the alternator to partially charge the batteries in noise senstive camping situations due to the idling V10 being way quieter than any generator.

When we're traveling after camping and starting out with the coach batteries down around 50%, the alternator takes about 3 1/2 hours to charge the coach batteries up enough such that the ammeter reads about 1/2 amp going into the coach batteries - which means that the batteries are fully charged.

The reason for the dual voltmeters - one for alternator output and one for coach batteries's terminal voltage - is to keep a close watch on voltage drop between the alternator and the coach batteries. If these voltage readings aren't real close to equal whenever the alternator is charging the coach batteries, it most likely means that the interconnect solenoid's contacts have degraded and hence the solenoid must be replaced ... this has happened to me twice in 13 years and ~71,000 miles of camping travel.

The PD converter algorithm almost meets Lifeline specs precisely, at 77f battery temperature anyway. Seems no aftermarket converters bother with temp compensation, and convincing others to forgo automatic 'stages' for manual voltage adjustment is urinating into the wind in this smart phone 'look at meeeeee!' era.

The PD boost to 14.4v every 18 hours from float(13.2v) is unrequired though, for AGM anyway.

My Thin plate pure lead Northstar AGM loves a high amp recharge from a well depleted state, holding ABSV until amps taper to low levels. It was rated at 90Ah new, I have 65amps of plug in charging source available, and regularly feed it that much, and my alternator can provide even more amperage.

I've never done Lifeline's conditioning procedure.
I have Done Odyssey's once or twice, but not back to back.

https://www.odysseybattery.com/documents/ODYSSEY_Battery_Reconditioning_Charge_Procedure.pdf



I judge performance by voltage retention under load for X Ah removed from the battery, and lately, with ~1100 deep cycles over the last 5.5 years, I can also judge its health, by how low amps taper to. When newer they could taper to somewhere lower than 0.05a at 14.7v with the charging source left at 14.7v, but now after many low and slow solar only recharges it will stop tapering at 0.9a at 14.7v then start climbing again. When I notice this occurence, that night I might intentionally discharge to well below 50% then high amp recharge ( 40 amps minimum) and then amps will again taper to 0.4 or less at 14.7v in a reasonable amount of time.

I've not cycled any other AGM for 5+ years, so I can't say whether what I notice with this Northstar AGM is applicable to other brands.

I do use this Northstar for engine starting too. A volt meter on my dash reveals just how low voltage drops during engine cranking which is ~140 amps of load. A mini load test every engine start, is how I view it. Even well depleted at 1100 deep cycles at 5.5 years of age, it has no issues starting my 5.2 liter v8 in mild ambient temps. When it does I will consider replacement after Odyssey's reconditioning procedure does not seem to be effective anymore.

I will have no Issue forking out the top $$ for a new Northstar AGM once this one can no longer meet my needs. It has been an exceptional battery in deep cycle and dual purpose usage, despite its marketed 'thin plates'.

Its all about proper recharging, and I would not have achieved this lifespan with less than 20% charge rate available, and would not have achieved it had I not been able to hold absorption voltage as long as required for amps to taper to 0.5% of capacity. This requires I use a manual charging source that caters to my whim, not what some beancounter decided was acceptable in some cubicle somewhere.

I do not really adjust voltage for temperature much, but I am mostly in coastal southern California where temperature swings are a tiny fraction that of most every other location on the planet.

High amp recharging will heat the battery. I think this heat helps break up any sulfation which might have been hardening. When over 80f outside I will lower absorption voltage accordingly when high amp recharging from a well depleted state. I've never allowed the battery to get over 105f and that occurence is quite rare, requiring high ambient temps and high amps applied for a long time from a well delpeted state.

As far as I can tell, 'drying out' of AGMS is largely hogwash. I have left mine at 14.7v + cumulatively hundreds of hours after it was already fully charged over the last few years. I can't precisely weigh the battery, but as long as it still mees my needs, I will keep cycling the snot out of it, and regularly apply high amps until amps taper to 0.5% or less of capacity.