Mex's 20% AGM Rule Sucks.

[BFL13]

Mex says deep cycle AGMs need to be recharged at a 20% of Bank AH rate even if they are not Lifelines (which do specify that).

My AGMs are not that brand, and no mention is made of a minimum charging rate in their specs, just a maximum (about 27%) at the charging voltage specified for "cycle use" (as opposed to "storage use" -might mean UPS duty)

So that's fine until you get into shallow cycling, where the batts don't get down to a low enough SOC to accept that many amps on a recharge. So now what? Are you supposed to run them down a bunch more before recharging them, so they will accept at least 20% charging rate?

EG, after four days off grid with my 450AH of AGMs, with solar and a general variety of draws on the batts from microwave, television, etc, all the usual daily ups and downs, when finally on shore power at home, and ready to get the batts to "true full", the bank starts off accepting 29 amps with the charger set to the spec 14.5v.

The story used to be that all you had to do was leave it there until amps tapered to 0.5a per 100AH of bank. That's easy, just watch the amps on the Trimetric come down and when the batts are full, crank the voltage down to 13.6ish,adjusted for temp.

BUT--29 amps on a 450AH bank is hardly 20%!!! So whatinheck are you supposed to do? (Actually, what do Lifeline owners even do????)

[landyacht318]

That specific Ctek product is a DC to DC converter which is supposed to take whatever voltage the vehicle is allowing, and transform it to 3 stage charging for house batteries, and also be a MPPT solar controller.

It is not simply a take whatever voltage supplied and provide 14.4v to house bank always converter.

I imagine a 14.4v always DC to DC converter could be done for much cheaper and a member here has done so on his 7 pin trailer harness.

Either way, absorption at absorption voltage takes considerable time, and more time as the batteries accumulate cycles.

So simply driving and supplying 14.4v is not the end all be all answer, as it might take 6 hours at absorption for amps to taper to 0.5% of capacity, and driving simply to supply 0.6 amps to a 99% charged AGM battery is insane.

Also note than unless equipped with the "$martpass" that Ctek is limited to 20 amps output so would only meet the 20% minimum, on a single 100Ah or less battery.

Beware of marketing, and the physics defying claims that marketers like to employ in their quest to separate you from your money.

The Ctek product might be OK in a small rig whose vehicle voltage cannot be manipulated for better battery charging, and whose house battery bank is small, but it is very pricey for what it is, and is by no means a solution to the AGM's 20%+ 'rule', or the fact that it requires a bunch of time to properly absorb a hard working daily deep cycled AGM.

If it holds a 85% charged battery at 14.4v rather than 13.7v, well that certainly is an improvement, but is it worth 300$?

A dedicated inverter on engine battery powering a grid powered charger, or a Megawatt or Meanwell power supply set to 14.4v, could easily be more effective for less$$, and the powersuppy can also be used on the grid when that is available for top charging.

I have a meanwell rsp-500-15 that I use as a converter, and bulk charger, and portable charger, and it is capable of 40 amps at any voltage from 13.12 to 19.2v. Rated for 500 watts It regularly outputs 600.

I've never run it from an Inverter though.

[MEXICOWANDERER]

An hour or two or three 14.4 per recharge cycle is OK. 14.4 for day after day long trips has me wondering. Couple long days with high ambient temperature and I would tend to raise my eyebrows at vehicle charging.

Control is Key
Effortless Control is paradise

[JimBollman]

Thanks for the additional info. I would have to check but I think my battery is connected with 10g wire currently. The 30 amps I mentioned was based on the charger/converter they have installed from the factory.

I have also considered biting the bullet and buying one of the CTEK 40-186 D250SA DC Battery Charger then I could charge at 14.4 volts going down the road. Very pricy.

The solar option got more complicated in that I don't have any flat places on the roof.

[NinerBikes]

MEXICOWANDERER wrote:
If you have to buy a



for fifty bucks on eBay

Set the pot for 14.4 volts then when you get home plug in the Megawatt for several hours. That'll make absolutely sure the batteries get topped off right then your converter can take over the float.

You do NOT need a converter change, and time spent at 14.4 volts at home is not that critical 3 hours, 5 hours then unplug the Megawatt. This will bypass the most common error in AGM management and can easily TRIPLE the longevity of an AGM. The best $50 you'll ever spend.

Hi guys, been gone a while with that Deka 155Ah surplus Telecom thick plate battery. Easy as pie to maintain. Put it on the Megawatt 350,s set the variable pot voltage to 14.4V with mega watt turned on, then turn it off, and connect the battery. Max amps I've ever seen that thick plate Telecom AGM battery take is 20 amps at 14.4V I'd say it's imperative to get it down to 40 or 50% SOC every year or two, and let it take 20 amps off the generator or the pedestal for maybe 4 hours. After that.... when I get back home, pull the battery, store it in the garage and as soon as I get home, put the Megawatt on it for 3 or 4 hours to let it taper charge down to anywhere to from .75 amp to .50 amp charge rate at 14.4V.

Battery just seems to keep on doing a really good job, I have to run it 2.5 to 3 days to get it down to 35 or 40% SOC, followed by 2 hours of generator time with the MegaWatt at 14.4V, then the rest of the day, the 150W 9 amp solar panel,again set at 14.4V gets to add another 40-50 amps, while camping. I try to do the generator and 20 amps is all she'll take thing a time or two on every camping trip. I always top off charge the AGM when I get back home.

I believe Mex is right, if I continue, I should see 10 years out of this battery, with the way I operate. Do an occasional 50% discharge, and set the volts to 14.4V and let it take all the amps it will handle to a 80% SOC, and then don't worry about the taper amperage rate, keep the volts steady. I feel a deep discharge helps stir up the battery chemistry. I DON"T do a hard drain rate on me telecom, running heavy draw in amps from it. I keep it under a 10 amp draw max, at all times. My Deka telecom doesn't like fast discharge rates, or fast charge rates, due to few plates, and the plates are very, very thick. Price I paid.... $125 for a near new 150 AH Telecom... I knew what I was getting into... works great for off the grid dry camping. Works great with the solar panel, for about a week... then it needs the clean up cycle, or a drive with the alternator on the Touareg, which also has an AGM battery, to get it topped off, to a new campsite. Lucky for me the Touareg also has that AGM battery and a max voltage that I can see on the Scan Gauge as 14.4 to 14.5V. Not enough to worry about, it just works well. The electric drum brakes on the trailer on hard braking session, seems to pull a lot of amps out of that battery.

[MEXICOWANDERER]

I sure would make things easy to do. Meaning you need minimum size wire to the battery clips. 12 gauge would do fine. A sixteen gauge power wire is plenty this allows the cords to be wrapped around the box and stowed easily. Use a 3 wire power wire with a ground.

If you're on the road a week every day, wait. When charging becomes intermittent then once a week with the Megawatt is plenty. When floating at home once a month is plenty.

You can tweak the potentiometer to 14.7 and use this thing to faster charge wet batteries too. When a converter or charger wants to lean on a shovel hook the Megawatt up and reduce finish charge time by 90% This really helps when using a generator.

[pianotuna]

I agree, you don't need more converter. I'd take the megawatt along on trips--its not that large.

I am all in favor of some solar however.

[JimBollman]

So I would just use the MegaWatt as a specialty battery charger at home for AGM batteries.

So how long can I be on the road before the topping off would be necessary?

I drive my Class B as a second car so it would get some lower voltage charging a few times a week even when we are not on a road trip. Would I add some top off time from the MegaWatt every so often even if I haven't discharged the AGM batteries from use?

[MEXICOWANDERER]

If you have to buy a



for fifty bucks on eBay

Set the pot for 14.4 volts then when you get home plug in the Megawatt for several hours. That'll make absolutely sure the batteries get topped off right then your converter can take over the float.

You do NOT need a converter change, and time spent at 14.4 volts at home is not that critical 3 hours, 5 hours then unplug the Megawatt. This will bypass the most common error in AGM management and can easily TRIPLE the longevity of an AGM. The best $50 you'll ever spend.

[JimBollman]

MEXICOWANDERER wrote:
JimBollman, you'll do fine. This is like of bunch of old ladies trying to figure out how to get the whitest wash...

Thanks Mex, I was hoping that was the case.

[JimBollman]

pianotuna wrote:
JimBollman,

What is your camping style?

How much capacity were you intending to add?

30 amps charging would easily service 150 amp-hours of battery bank.

I got tired of laying in the snow to check my flooded. I'd NEVER switch back.

As the batteries charge they start to "push back" and limit the charge rate automatically.

On a flooded jar that happens at 85% state of charge--limiting the rate to 15 amps per 100 amp-hours of battery bank. On an AGM the number is higher--tapering of charging probably happens at 92% soc.

There is at least one member here who uses a 'stock' PD converter and it successfully charges his agm bank.

As for the rest of us battery nuts, we love to "dance on the needles".

The majority of our camping is single nights and then 4-8 hours of driving before we stop again. Most of the time we stop in campgrounds but not always and not always with electricity. Anytime we are camping for more than a day we are connected to power accept once a year in early October when we camp 4 days without power and generators are a no no. Our new rig has a compressor frig and my first thought was to have enough power to get us through but decided that was not reasonable and probably not worth the cost of solar for once a year so we will probably just go with an ice chest for that trip.

With computers to charge and normal camper needs I figured two batteries will get us through the 4 day without any problem, that is what our old rig had. For years we scraped by with one. I need to measure how big the existing box is and I figured I would get two AGM batteries of that physical size, I see no reason to go smaller than the space available. I'm not trying pinch pennies.

The frig draws about 3.5amps when running. Unless we have a really warm October, I'm guessing it would only have a 25-40% cycle rate. So the frig would need 85-135 amp-hours all by itself for 4 days, if we used it.

I have converted to LED lighting and we don't use much light while camping anyway.

[MEXICOWANDERER]

JimBollman, you'll do fine. This is like of bunch of old ladies trying to figure out how to get the whitest wash...

[pianotuna]

JimBollman,

What is your camping style?

How much capacity were you intending to add?

30 amps charging would easily service 150 amp-hours of battery bank.

I got tired of laying in the snow to check my flooded. I'd NEVER switch back.

As the batteries charge they start to "push back" and limit the charge rate automatically.

On a flooded jar that happens at 85% state of charge--limiting the rate to 15 amps per 100 amp-hours of battery bank. On an AGM the number is higher--tapering of charging probably happens at 92% soc.

There is at least one member here who uses a 'stock' PD converter and it successfully charges his agm bank.

As for the rest of us battery nuts, we love to "dance on the needles".

[JimBollman]

You guys are scaring me. Was thinking of switching to AGM batteries and figured I would have to change my onboard charging system. Since a lot of the charging will also take place on the road how do you control the current from the alternator? All my cabling is setup for 30 amp max charging and now I hear I may need to charge considerably above that.

How much loss of life do you get on AGM batteries if you break some of these rules? I'm mainly considering the change because my batteries are located underneath in a hard to access spot for normal maintenance.

[pianotuna]

A reflector system is not a concentration system. It is to correct for off axis exposure. In the far north panels are orientated to take advantage of the bounce off the snow. It makes a large improvement of the harvest.

Even an on axis installation is not going to approach the testing done in labs as to "number of suns".