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Old 01-14-2015, 05:39 PM   #1
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Join Date: Aug 2010
Location: Minnesota
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Default Top notch charging with basic equipment

Marko's excellent battery type summary inspired me to put one up about charging systems that I have been working on. It is the result of our years long testing of our, quite complicated, system, but uses very common parts, and would be easy to use. If I were building a single battery bank setup now, I would chose this over our system based on cost and simplicity, but being able to get comparable results.

Top notch charging with basic equipment.


This is a good question, and the answer IMO is "it all depends". Top notch charging requires some effort and some basic equipment. Benefits are achieved, but some folks may prefer to take the detriments of poor charging rather than do what is required for top notch charging. I don't have any issue with either method.


Increased usable battery capacity without adding batteries and longer battery life. Less water to add in wet cells.


Some manual input needed on a regular basis. Having the correct charging components to make it work.


If you use your batteries down to 50% SOC (the typical standard), and are only getting them charged to 80%, you will gain the difference between 80% and 100% SOC or 66% more usable capacity without adding any batteries. That is quite a lot for no added batteries. We noticed a huge difference in how soon our voltage started to drop when on batteries once we got totally full all the time.

The longer battery life is harder to quantify. Most would say it is somewhere in the 2X to 5X extra life by using top notch charging. If you are chronically overcharging AGMs, you will gain more, chronically undercharging either kind you will gain more. Overcharging wet cells, you will gain less. When a set of Lifeline AGMs can be $1000 2X or life gets to be a pretty big number.


From what we have learned in our several years adventure with chargers, controls, batteries, etc, it looks like you can get very good battery charging, without over or under charging, with some very common parts. It is also very likely that many folks already have the necessary items, as they are pretty common, and for them it would only be how they use their systems.

The whole idea is based on that the only (my opinion) practical way to tell if a battery is fully charged is to look at how many amps it is accepting at absorption voltage and normal temperatures (or temperature corrected).

The system we built and did all the testing on is much complicated than is necessary for getting good charging, as it has to handle multiple battery banks of mismatched batteries and is intended to be almost fully automatic. The system described here requires a bit of manual input, but if that input is not done, you don't wreck anything. You just are back to less than optimum charging, with no other penalty.

For a single battery bank setup with shore charger and no solar, you would need:

*Progressive Dynamics charger with Charge Wizard
*Trimetric, or other battery monitor that runs off a shunt

that's all

If you want to add charging off the vehicle alternator while driving add:

*Battery separator that can be shut off, or modified to shut off (the standard coil ones that come on most B's work well if modified a little)

If you want to add solar to all of above:

*Add a Blue Sky controller with Pro Remote
*Put an on/off switch on the solar panel wiring from the panels to the controller

If you do the Blue Sky, you can won't need the Trimetric meter as the Blue Sky has it built in

As an alternate to the Blue Sky, if you have the Trimetric already, it appears you would be able to use the new Trimetric solar controller added to the meter and gets most of the benefits, except it is not an MPPT controller. I haven't tested it.

There are probably other brands that would work well also, that I don't know about. If they function the same as this stuff, they would certainly be fine.

I think many folks already have much of this in place, and may only need minor programming and setup of it to be good to go.


As mentioned, this all is based on the battery being totally full, and not overcharged, when it first hits an input amp reading (at absorption voltage) that is as little as it will ever take at that voltage. Blue Sea calls it ending amps, and the battery will pretty much continue to take that much amperage until the overcharging kills it.

*The goal is to make sure that the battery gets to that amperage on a regular basis, and is not left at absorption voltage after it gets to that amperage.

That's all there is to worry about.

About the only real extra thing you need to do is determine what the ending amps of your battery, or batteries, is. You only have to do it once, but the number you use may change over time as the batteries age. You will see the change as you use the system, so it is not really more work.

To determine the ending amps using the PD charger. Plug it in and let it run. It will get to absorption voltage (usually 14.4v) after a while. When it gets there watch the Trimetric meter for amps going into the batteries. When the amps quit going down, you are at ending amps. If the charger goes into float (13.6v or so) before the amps quit getting lower, use the Charge Wizard to put it back into absorption. Repeat as often as necessary until the amps quit going down. You are now done and know the ending amps for your batteries, off your charger. It will usually be somewhere in the .5 to 3% of the battery capacity AH, per the manufacturers, but that is a quite large range. That is why it is better to determine your own.

If you are using the vehicle engine to charge also, it may run at a different voltage than the shore charger, so right after determining the ending amps off the charger, you can easily do the same for off the alternator, as you know the batteries are full. Take it off of shore power and run some load to take the surface charge off. Start the engine with the separator connected. Note the voltage, but it doesn't really matter much except for future reference, and let the engine charge the batteries until the amps into the batteries again quits dropping. You now know the ending amps at that voltage, off the alternator. The alternators will change voltage based on conditions so this ending amps will be less accurate, but for how you use this part of the process, it is more reference anyway.

If you have the Blue Sky, or other solar charge controller that is similar, you can program in the charge voltages and ending amps. Just match what you got for the PD charger, and set the minimum absorption time on the solar very short, like 15 minutes, and maximum time long.


On shore power, plug in and watch the battery meter amps. Use the Charge Wizard to switch to float when you get to ending amps, or if the PD times into float before you get to ending amps, use the Wizard to put it back into absorption until you get to ending amps, and then put into float. At that point the batteries are totally full and not overcharged, and you are in float so you don't hurt the batteries.

Off the alternator, just have the separator on so the batteries are charging and watch the battery meter. When you get to the ending amps that you know for that voltage, or if they just quit dropping, disconnect the separator. At this point the batteries are full, not overcharged, but also not getting replenished for what the coach is using (like the high output for a 3way frig on DC). There are ways around this that I won't get into here, and solar will also take care of it, in most cases, if you have it. The simplest way to handle it is to turn the separator back on ever once in a while to retop off the batteries, and shut it off again. If you can see the meter from the driving position, and have the separator switch there, it is very easy to do.

If you have solar like the Blue Sky, it will mostly take care of it's self, and go to float based on the amperage going to battery (which you set already). It is great when driving because you can turn on the high output from the alternator to get the battery full, shut of the separator, and the solar will carry the coach use at float voltage and not overcharge the batteries.

All of these interactions with the system are extremely non-critical, and not doing them basically puts you back to the normal type systems that are in most RVs out there. Missing the exact times by an hour in most cases really doesn't change much, from what we have seen, so obsessing is needed only if you like to obsess

We did the testing of charge and overcharge based on specific gravity in wet cells to determine if the batteries were full, and water use in the batteries to assess how much overcharge they were seeing. Neither of these tests are available if you have AGM batteries, so using the ending amps as a judge of charging is about all you can do easily, that is also accurate. Wet cells and AGMs should react very similarly in all of this, but the AGMs will get to fully charged faster, in most cases.

For reference, what we found in our, and other systems, that were in use.

People on shore power all the time with non PD chargers were chronically undercharged in most cases (as Handybob also noted in his articles)

With PD chargers on shore power, over or under charged mainly was determined by battery bank size and frequency of plugging in. There seemed to be less under charge with PD chargers unless the battery bank is big.

Solar chargers programmed like the Blue Sky would almost never overcharge anything, but could undercharge if the solar array is too small or it was cloudy.

Charging off the alternator is one area that almost never hits the right charge amount. If you have a lot of AH to recover and don't drive far, you won't get recovered (wet cells and AGMs take a couple of hours to get the final 5-10% of fill). If you have full batteries, when you start, or drive long days, you can easily put 10-12 hours per day of overcharge on the batteries, which is pretty harmful. We could use over 1/2 the water in our batteries in a week of driving at 14.4 volts. There are no charging controls on 99% of alternating charging systems for coach batteries in stock configuration.

Watching our wet cells would seem to confirm that you don't need to get to ending amps on every charge cycle. Getting fully to ending amps every 3-5 days gave no sign of battery deterioration, and there are numerous places that say once every week or two is OK. I think this is pretty reasonable, as long as you are not doing deep (over 50%)discharges all the time.

Comments, suggestions, information from all would be greatly appreciated as this is still a work in process.
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Old 01-14-2015, 08:08 PM   #2
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Default Re: Top notch charging with basic equipment

Great article - thanks for posting it.

Monitoring the ending amps seems like such an easy and foolproof way to know that your batteries are charged.
This type of monitoring should be standard equipment in today's high tech RV's.

Good point about forcing a PD charger back to 14.4v if it switched to 13.6v Normal mode.

In this video my PD charger is in Normal mode approx: 13.6v but in the upper right you can still see the "amps in" dropping rapidly.


I don't remember the specifics of what I was testing - probably just trying out the meter with various loads.

You could use a clamp on ammeter also.
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Old 01-14-2015, 08:41 PM   #3
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Default Re: Top notch charging with basic equipment

Yes, good point about being able to use any ammeter you have or get. The only requirement is that it has to go in the line to the batteries, not just off of the charging line from the battery charger. If you take it off the charger line, any loads from use in the van will make you get the wrong reading.
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