AGM charging: battery-to-battery, shore charger, struggling on best approach

[Vermonster]

Apologies as I know the whole AGM charging thing has been beat to death...I've been digging deep to find the proper way to charge my AGM second battery on the 4Runner. Given I only get 14.1-14.2 volts from the stock alternator I know I'd need some additional hardware or another creative approach to provide the ~14.7 volts the AGM wants (the starting battery is standard LA) .

Given driving patterns (most drives < 1 hour), I know a shore power option is needed that can supply the proper voltage and current.

So far I have identified several options.
#1. Ctek D250s dual. This will boost alternator voltage to 14.4v at 20amps..which is a lower voltage than desired so shore charging once in a while is a good idea. Lots of shore chargers examined but very few have sufficient voltage in bulk phase. Iota with IQ4 comes closest at 14.8 bulk 14.2 absorb.

#2. Sterling BBW1212 battery-to-battery charger. This will boost alternator voltage to 14.8 volts and supply 25 amps. No special shore charger needed as can attach standard 14.2 volt shore charger to starting battery and have Sterling unit boost for 2nd (house) battery only.

#3. Screw either of the two voltage boost options and make sure to attach shore power weekly with a charger like the Iota that will make 14.7v and 20+ amps.

I will probably run a parallel heavy cable with relay so batteries can be combined for self jump if starter battery dies.

Anyone have thoughts? A better (or cheaper) approach? I'm leaning toward the Sterling unit at $280.

Does anyone think 14.8 volts vs. 14.7 is an issue? (I think I would rather err on the side of high voltage given how many off-grid folks I see killing batteries with insufficient charge).

Can anyone suggest a better shore charger than the Iota + IQ4?

 

[kb1ejh]

So here is what I did, I haven't seen smoke yet and it has been working fine so far... I have a National Luna PPP as a secondary power source with an Optima AGM battery in it. The PPP is linked to the vehicle battery to charge when I am on the go and can be used to jump the vehicle if needed. To charge/maintain the PPP while it is parked at home I picked up a BatteryMINDer 128 that will charge, maintain, desulfate the battery(ies). It is connected to the vehicle battery via the PPP so both get charged, maintained, desulfated while parked at a 110v source. I also have the ARB fridge powered by the PPP when on the go. When at a 110v site I just run the shoreline to the truck and with a 3way 110v splitter the BatteryMINDer is powered and the ARB will run off 110v and keep things cool. I use a lighted 3way splitter so I know the power is going to the charger and ARB. The BatteryMINDer was about $150. I am sure there are a 100 other ways to do what you want but this works for my situation.

 

[pugslyyy]

I'm also looking very closely at the Sterling (the BBW1260)...

Defender has some of the best pricing I've found. If anyone can do better clue me in!

 

[DiploStrat]

Beat that Horse!

As one who has beaten this dead horse for years, may I suggest that you read a few of the articles on my website, linked in the signature.

Lead acid batteries are easy. You must bring the battery to the maximum voltage suggested by the manufacturer and hold it there for a L O N G time. This is done to assure a full recharge and to prevent sulfation. So, you need two numbers:

-- The absorb voltage specified by your battery manufacturer at 20C/70F. For modern open cell batteries, this is typically about 14.7v and for AGM (sealed) batteries, typically about 14.4v.

-- The maximum sustained voltage of your vehicle's charging system. For Chevrolet and, I suspect, Ford and RAM, this is around 14.4v. Some Mercedes Benz and Toyota products are reported to top off at about 13.9v.

Generally, means that the typical US pickup or van has no need for a secondary charging controller - just big wires and a long drive.

If your vehicle's voltage is below 14v, then you may want to raise it. There are several options.

-- The easiest, used by many Toyota owners, especially in Australia, is to simply raise the voltage to whatever you need. The easiest way to do this may be with something like this: http://www.mechman.com/accessories/...voltage-boost-module-for-square-4-pin-toyota/ (They make several other options, but nothing for MB.)

-- A more expensive option is a battery to battery charger, B2B. CETK makes a nice model, the D250S which can be combined with an integrated smart relay (SmartPass). This gets you high amps and high final voltage. As a bonus, it has a small MPPT solar controller. Sterling Power has a wide range of B2B units, up to 120A charge rates. ($$$$$)

Depending how long you will drive everyday, a solar charger and shore power may be a much better/cost effective option.

Only you can determine which approach will best meet your needs.

Parthian Shot: NONE of this applies to lithium.

 

[dwh]

Thoughts...

You can't run a DC to DC charger, such as the CTEK or the Sterling, at the same time as the split-charge relay (combiner solenoid). You would create a feedback loop. You could still rig the solenoid, but it would have to be manually controlled and disengaged while the charger is operating. Or just carry jumper cables for the once every 10 years when you need to self-jump.



The actual proper charging voltages for any lead-acid battery are temperature dependent. Warmer temp, lower voltage : colder temp higher voltage. Bulk voltage for your battery might be 14.7 if it's parked in the shade with the engine off (cool), and lower than that if the engine is running (hot).

The CTEK and Sterling both have remote battery temperature sensing (RTBS) and will adjust the voltage up and down depending on temperature.

The Optima Yellow Top charge specs list 14.7v for cyclic applications, but they also show that it can handle higher voltages:

https://www.optimabatteries.com/en-us/support/charging/charging-tips

So no, a .1v difference isn't going to matter in your situation.

 

[eviioiive]

I have a $20 inverter wired to a $15 low voltage disconnect. Noco G3500 was $50 and the AGM motorcycle battery was $40.

I leave it plugged in on trips and it has been working pretty well for the past couple years

 

[Vermonster]

BatteryMINDer 128. Thanks for bringing to my attention. Only delivers 8 amps, but will do 14.7 volts. Makes it slightly better on paper than the largest Ctek that does 14.7v. I wish a higher amp version was available.

Source for Sterling stuff in the US. Agree. Defender is Bay Marine. Low prices and flat $9 shipping. Better pricing than I can find anywhere else.

The Ctek D250S seems to only provide 14.4 volts even with the Smartpass. Maybe I am missing something?? The Ctek is only $70 difference in street price from Sterling. Seems like about the same money...although I do like the integrated MPPT solar controller of the Ctek (acknowledging it's voltage input limitations).

Regarding lithium. Here in the north (NH) you'd be crazy to put lithium in vehicle that sees winter action (not suggesting you were thinking it was a good idea). We've gone to lithium at our field research site (cabin) due to constant undercharging of FLA from Nov-Feb. Works well, but only with a heated battery box and automatic generator backup in case the heater burns through the power supplied by the solar array. Big $$$$. Understanding of limitations and very high quality battery management system is critical if you don't want to destroy your multi-thousand $$ investment. Our system requires constant tweaking to ensure power is there when it's needed.

Understand about not running DC to DC charger at same time as the split charge (combiner). I will isolate the Sterling unit using a Solenoid so it can be shut off if batteries need to be combined for self-jump. I wish I could get by with jumper cables for the self jump; unfortunately so many research staff I work with unload the vehicle that invariably the cables will be left behind just when they are needed. Anything mission critical needs to be permanently attached.

I wish I could get by with just a motorcycle battery and a smaller charger. Unfortunately need to run a fridge in summer and self-jump at 40F below in the winter means a larger battery is needed.

At this point my dream equipment is a fully customizable charger (like a top end Morningstar) but in a small enough package for a SUV/truck. I don't think anyone has yet produced such an item. The charger manufacturers seem more enamored with how many stages they can claim rather than meeting the battery scientists' specifications.

 

[DiploStrat]

Don't Make This Too Hard

Again, yer making this way too hard.

-- Which AGM are you using that requires 14.7v? Use a different battery, Lifeline, for example, that only specs 14.4v. Again, this is at 20C. Also, it doesn't matter which charger gets the battery to your desired voltage, so long as one of them does it. So even if your alternator does not achieve the final voltage, your solar or shore power charger may. If your typical drive is less than one hour, you aren't going to get any real charge from the alternator anyway.

-- You can certainly install a bypass around a B2B, either a manual switch or a relay. Just remember that when that circuit is closed, you will not see any boost. To quote Charlie Serling, Jr.

"The voltages on the input and output terminals of the BB simply reflect the input battery terminal and the output battery terminal's voltage.

Therefore, you can just put a simple bridge between in the input terminal and output terminal. If you put a switch in this bridge you can toggle between bypassing the BB altogether and utilizing it.

Therefore, when you are wanting current to flow back to the starter, close circuit the switch in the bridge. When you are driving along and you wish the BB to operate the open circuit the switch."
​

Which, of course, is what dwh just posted. The only difference is that Charlie actually makes B2B's.

Finally, how big a battery bank, and how big a drain and for how long? If the battery is 100Ah or less, just get a decent shore charger and use it once a week.

 

[rruff]

Again, yer making this way too hard.

In the interest of simplicity (and greater deep cycle capacity), is there a reason not to ditch the starting battery and have two identical deep cycle AGMs?

 

[Vermonster]

I agree. This seems overly complex and KISS is better.
Challenge: I have very limited space for 2nd battery; height over 8" will cause me to do major work under the hood. So I would prefer a single size 34M (68Ah). This limits me to Odyssey, Northstar, or the latter re-badged as X2. [Edited to add, Optima also has a 34M but due to prior bad experience I am avoiding.]

Regardless I think I will never get a decent charge from the alternator given my short drives, and so should keep it simple under the hood and buy a good shore charger to be used 1x per week.

Does anyone have a shore charger to recommend other than the Iota with IQ4 that will provide 25amps at 14.7 volts?

Edited to answer my own question. Another option (with a more portable form factor) is the Odyssey 20A charger: http://www.odysseybattery.com/documents/ODYSSEY_battery_charger_manual.PDF

 

[pugslyyy]

I recommend adding a charging/jump starting plug so that you don't have to raise the hood to connect to the battery. Anderson SB175 connectors work really well for this

 

[DiploStrat]

In the interest of simplicity (and greater deep cycle capacity), is there a reason not to ditch the starting battery and have two identical deep cycle AGMs?

None at all. This is a very valid approach for a smaller "jeep" style vehicle. Usual caveats:

-- With two batteries permanently in parallel, they need to be same model, age, etc.

-- Batteries must be compatible with vehicle charging system.

-- With no isolation, you must be aware of your consumption, so that you don't strand yourself. (Carry a jump pack for emergencies?)

All of that said, you can save a lot of money as you don't have the cost of an isolation system.

 

[DiploStrat]

… I have very limited space for 2nd battery; height over 8" will cause me to do major work under the hood. ...

At under 100Ah you are talking 50Ah maximum usable consumption, unless you choose to hammer the battery. Depending on your needs, you may be better off simply using an open lead acid battery and throwing it away after a year - no reason to spend for AGM.

In any case, if you only drive for one hour or less, just go with a key controlled relay (see the thread in this forum) and get a 20A or less shore charger.

Again, what are you trying to run and for how long? The answer to that question will determine the size of your needed battery bank. Get this right before you worry about the difference between 14.4v 14.7v.

 

[rruff]

None at all. This is a very valid approach for a smaller "jeep" style vehicle. Usual caveats:
-- With two batteries permanently in parallel, they need to be same model, age, etc.
-- Batteries must be compatible with vehicle charging system.
-- With no isolation, you must be aware of your consumption, so that you don't strand yourself. (Carry a jump pack for emergencies?)

I was thinking of two 225ah 6v AGM batteries in series, to serve "house" loads and starting both. Main charging will be solar (160W panel) with weekly driving (~3hrs). I will be monitoring the batteries and keep them above 50%. Now that I think about it maybe it would be better to use two 12v batteries in parallel so I could still run if one of them died for some reason.

I've been told that the batteries will not get to 100% charge without many hours on a charger (which in my case will never happen) and will sulfate and die rather quickly. I'm skeptical though, since the way I'd be using them is typical of an offgrid solar house. Thoughts?

 

[DiploStrat]

I was thinking of two 225ah 6v AGM batteries in series, to serve "house" loads and starting both. Main charging will be solar (160W panel) with weekly driving (~3hrs). I will be monitoring the batteries and keep them above 50%. Now that I think about it maybe it would be better to use two 12v batteries in parallel so I could still run if one of them died for some reason.

I've been told that the batteries will not get to 100% charge without many hours on a charger (which in my case will never happen) and will sulfate and die rather quickly. I'm skeptical though, since the way I'd be using them is typical of an offgrid solar house. Thoughts?

Two thoughts:

-- Probably easier to wire up with two 12v batteries in parallel. This would allow you the option to install an isolator should you wish. If you have two 12v in parallel it is unlikely that you would ever notice if one died; they would die together.

-- The need to achieve a 100% charge with lead acid is real and yes, it takes hours. That said, this is where solar excels. You can expect about 5A of charge from a 100w panel in good sun, call it six hours a day; call it 25 - 35Ah of charge. Assuming a good solar controller with the proper voltages, your batteries should be fine.

Remember: Alternator for bulk charge, solar for absorb charge.