Converters vs Chargers - Opinions Needed!

[Andrew Herrick]

So, I know that Progressive Dynamics is kind of a cult around here. I like them too But ...

My understanding is that the PD ChargeWizard isn't truly optimized for A) charging AGM batteries, which are often best charged at up to 14.8 volts (PD CW is capped at 14.4 volts), and B) there's no temperature compensation to adjust voltages depending on the ambient temperatures, which, within a half's hour drive of my home in southern Utah, can vary from -20 degrees to 110 degrees depending on the season!

I've been researching other brands - Parallax and Samlex mainly - but I haven't found anything that really stood out from PD. Parallax does offer Temperature Compensation with some of its converter/chargers, but the algorithm doesn't sound ideal. Plus, they usually cost more, and for equivalent performance, I'd rather go with PD right now.

My thought process is that a better charger might pay for itself by extending battery life. No one likes spending $200+ on a decent AGM battery.

Problem is, like I said, I haven't found any RV converter/chargers that truly excel at both.

So a possibility is to split the functions. Get an AC-DC constant voltage power supply to run the 12-volt system, and then get a separate 12v charger. Personally, I like NOCO Genius chargers, but CTEK is good too. Plus, the CTEK 2500 even has a "12v" power supply mode, regulated at a constant 13.6 volts to mimic a full battery, that can put out up to 25 amps to power 12v functions. So it's kinda a converter/charger as well, only it seems to be a much better charger! But .. it can't do BOTH functions at the same time! Grr.

Anyways, I'd like to hear thoughts on this. Namely:

1. Am I blowing smoke? Do we think a better charger will extend the lifespan of an AGM battery long enough to justify its costs? Or is more of an "on-paper" difference?
2. I suspect the CTEK 2500 can't double duty as a converter/charger because it can't accomplish both functions simultaneously, but I'd love if someone can prove me wrong.
3. If I want the best, should I split functions by getting a good converter AND a separate charger?

Thanks in advance,

[lfhoward]

I went the route you describe. I have both 12VDC and 120VAC in my trailer, and I have a separate battery charger and inverter rather than a single power unit.



The charger is a smart charger that can fast charge at first and then provide float voltage to keep the batteries topped off. It has a 15 amp max charge rate, and a built in 3 amp converter on it that can run the interior DC lights without drawing from the battery when the trailer is plugged in.

(These days I don’t use the battery charger much because I installed a solar panel and charge controller, which keeps the batteries topped off pretty well by itself.)

The inverter is a 1000 watt pure sine wave unit that provides clean AC power when I’m off the grid. Usually everything I use while camping is DC but there are a few things that need AC like certain power tools.

I guess a single power unit would have saved space, but this way I can upgrade or replace different parts of the system individually if they ever malfunction.

[absolutsnwbrdr]

I don't know about the temperature compensation, but there's a jumper on the PD4135 that should be moved if charging gel cell batteries. I would imagine the 4045 is the same.

[Trebor English]

For the temperature compensation changing the ambient temperature doesn't matter much. The battery temperature won't change much in a half hour of driving. A half hour hour of 50 amp charging, 600 watts, will bring the temperature up substantially.

As I see it the main problem with a combined converter charger is that it can't see what's happening. Ideally the battery should charge at the constant absorption voltage until the charge current drops to 1% or some other small fraction of the battery capacity. At that point the battery is full and the constant voltage should change from the absorption level to the float level. However, the battery is connected to lights, phone chargers, laptop computers, fans, etc. How can the converter charger discriminate between current going to the battery and current going to loads?

Sometimes "smart" chargers are used as converter chargers and they do things like shut off and flash an error code when the water pump comes on. Suddenly the voltage drops, charge current increases, and the charger decides something is wrong. A battery shouldn't behave that way. The problem is that it is not just a battery.

Several years ago I looked for a charger that would deal with this. I found one that connected to the battery and all the loads connected to the charger. That would allow the charger to have a shunt resistor in the battery charge path to measure the battery current separate from the load current. I contacted the manufacturer to ask if that was the reason for connecting the loads to the charger. The response was inconclusive marketing double talk.

I was also looking for a charger that could connect to an external shunt resistor to monitor battery current to achieve the same function. I didn't see any.

Solar charging systems have similar issues. Battery charge monitoring systems have shunt resistors to measure battery current. Balmar Smartgauge does it with just looking at rising and falling voltage. Some charge controllers get rather fancy.

Another problem is that loads get exposed to extreme voltages particularly with AGM batteries. Some AGM batteries really like high charging voltage and it does really help maintain capacity and avoid sulfation. Equalizing flooded batteries is similar but it is occasional not every day, and manual so sensitive devices can be turned off.

The bottom line is that actually using the electrical system disturbs everything and ideal will never happen. Good enough or adequate need to be the goal rather than the perfection of the battery manufacturer's specifications. I have a 13.8 volt 20 amp power supply and a 100 watt solar panel. If I am near a power plug and plug in the extension cord the battery stays at 13.8 volts and doesn't ever discharge so no charging is needed. 13.8 volts is poop for charging but it is plenty high to not be needed to charge. If there is no plugging in then the dumb $15 solar controller is set (manually) to 14.4 volts in summer, 14.8 in winter. Charging happens until the sun goes down. The dumb charge controller has no current sensing and doesn't shut off prematurely. This works fine with my group size 24 75 amp hour flooded deep cycle $80 battery.

As to question number 3:
3. If I want the best, should I split functions by getting a good converter AND a separate charger?

Yes but only if you get a big switch so that all your loads connect to either the battery (when not plugged in) or connect to the converter.

[bdosborn]

Have you looked at Xantrex chargers? AGM settings, temperature compensation, PF correction as well as the ability to equalize the batteries. I like everything but the price.

Xantrex Linky

I just ditched my PD 9140 with a charge wizard in favor of an Iota DLS-45. I wasn't happy with the battery life I was getting with the PD (barely 3 years despite never going below 30% Depth Of Discharge). I'll let you know if it works any better in a couple of years. Have you thought about how you use your battery? A Bogart Engineering Trimetric TM-2030 RV battery meter will track amp-hours so you don't discharge your battery too much.

Trimetric Meter

Bruce

[Andrew Herrick]

Thanks to everyone who has responded!

LFHoward, looks like a nice system you have there. I agree: It's nice to have separate components so you can upgrade what you wish. I only have one tiff, and it's a minor one - but I wish the converter was capable of supplying more than three amps to 12v loads while charging the battery. That won't run much more than lights and maybe a fan on the low setting. Still, my interest is piqued. What charger is it?

It seems that separating components can easily lead to overkill redundancy? In theory, it might be optimal to have a smart converter, dedicated battery charger, and solar charge controller, but that's a lot of money for three components all trying to do the work of one. I need a "master" converter/charger that can do everything I want!

[Andrew Herrick]

Trebor, that's some valuable information. You've really helped clarify the situation. The only suggestion I'd make is to make the "big switch" a relay so that manual oversight isn't necessary. My campers go out to all sorts of customers, some of whom can't tell a volt from a potato , so I avoid "dumb" components where possible.

And just FYI, my comment about ambient temperature wasn't in reference to temperature changes over the length of an individual battery charge. What I meant is that, in southern Utah, extreme annual temperatures range from -20 to 115 or so, and a temperature-compensated charger will work best at those extremes - especially for AGM batteries. I believe that's correct? See this link for more info: popupbackpacker.com/state-of-charge-your-camperrv-may-be-killing-your-battery-bank/

[Andrew Herrick]

Bruce,

I'm certainly no expert on Xantrex, but yes, I've browsed their product lines. Pretty impressive! If I only I could convince all my customers to shell out $$$$ for an inverter/charger :p

*EDITED* I've been crash-coursing on the Xantrex TrueCharge2 charger. I had run across it before, but I'm refreshing my memory. Also, very impressive! A worthy competitor to NOCO or CTEK.

The one potential downside is that a dedicated battery charger forces system redundancies. I still have mixed feelings about separating the converter from the charger, because there's a big part of me that likes the simplicity of the combo, but ... it seems like that's the yellow brick road to higher performance.

If I was building for myself, them I'd have no problem using a good meter to monitor battery performance. But again, not all my customers know much about electrical systems, so I need things like flashing LEDs to communicate when an AGM deep-cycle battery has reached 50% DOD.

* * *

Again, thanks to all! While it sounds like an automated individualized system - dedicated converter, dedicated temperature-compensated battery charger, and relay system - would work the best ideally, it also sounds like it will certainly be more expensive. It might not be worth it to the weekend warrior, but certainly worth it to anyone who travels extensively or travels in extreme weather.

Here's a tangent: I suppose, if all I'm after is lower long-term costs, it might be most cost-effective to just install a low-voltage disconnect (with manual override) to cap DOD at 50-60%?

[Aguyfromohio]

Have you looked at the Aims Power Systems units?
We have purchased their 2000 watt inverter charger with transfer switch

https://www.aimscorp.net/2000-Watt-Pure ... arger.html

It seems to do everything you mention for about $600. Smart charging with temperature sensing on the battery, low frequency inverter with 300% surge, lots of adjustment for battery type and charging limits, low voltage cut-off...

Although we bought a pair we have not yet installed them or lived with them so I can’t make any recommendation...hope we haven’t made a mistake.

[John61CT]

A quality high-amp charger will do everything even the smartest "converter" can.

Don't integrate distribution / CP panel or automatic transfer switch is all, more DIY approach but IMO gives more flexibility / choice that way.

Inverter should def be kept separate IMO

[John61CT]

Xantrex products are great, but corporate attitude to service after warranty really sucks.

They consider units under $3000 to be throwaways, not worth fixing.

[John61CT]

LVDs are cheap at low amps. Best if setpoint is adjustable.

Grouping circuits by "how essential" lets you shut down entertainment first, then freezer, leave navigation / safety alarms going much longer.

[Aguyfromohio]

A quality high-amp charger will do everything even the smartest "converter" can....

That point has confused me for while.
If the system has a battery powering the 12VDC loads and has a charger capable of, say, 20 or 30 amps, it seems like the 12VDC power bus should be held up by the charger through the battery when shore power is available and the battery is low. Perhaps some folks prefer low amp chargers and need the converter, but otherwise I don't see the functionality of converting 120 VAC shore power to 12VDC.
Lots of smart people around here buy them, so I must be missing something.

[Aguyfromohio]

...They consider units under $3000 to be throwaways, not worth fixing.

That's the good news and the bad news of modern electronics. We get very capable products at ever lower prices, but all the circuitry now is surface-mount electronics which are not really repairable in any practical way, and the profit margins are pretty slim. For devices under a few thousand dollars it does not make anyone any money to try to fix them. Repairing electronics is only profitable for the real expensive stuff.

Even then the little piece parts become unavailable. I work with large industrial things like variable-frequency drives for 1,000 hp motors, and repair is always a headache. You can buy a $75,000 VFD from Siemens or Rockwell, and in 3 years when you need to fix it parts are not available. Some little tiny surface-mount chip the size of a match head has gone out of production and is no longer available world-wide. When the last batch of circuit boards is sold out, the mfg can't build you another one for any amount of money. Sorry for your bad luck, just pay $75,000 for an all-new unit. Here's a Rockwell Automation website where they let their industrial customers down easy, warning them of end-of life. Plant managers pay people to watch these site trying to guess how many spare parts to buy while they still can.

https://www.rockwellautomation.com/glob ... rview.page

[Trebor English]

Here's a tangent: I suppose, if all I'm after is lower long-term costs, it might be most cost-effective to just install a low-voltage disconnect (with manual override) to cap DOD at 50-60%?

Since the campers are for rent and not your own use everything is different. Something that is "best" on paper, like a power supply and a battery charger and an automatic transfer switch, is not good at all for what you want. It's too expensive with too many possible failure points.

Look at what golf courses do. They manage a fleet of golf carts. Cost is a paramount concern. They use flooded lead acid batteries. Since they have control over the maintenance the batteries never go dry. Paying 150% to 200% for AGM batteries is a non starter. Flooded batteries are more robust, more tolerant of abuse, and actually testable with a hydrometer. AGM batteries are best in the environment where watering is impossible. Otherwise, they are harder to charge, have all the lead acid deficiencies of poor performance with partial state of charge cycling and slow charging to finish the last 20% and early death due to sulfation. The "advantage" of being mountable sideways is of no value if a flooded battery can fit upright. The "advantage" of not leaking acid when the case is ruptured is of no value if a flooded battery can be mounted in a plastic box to contain the leak.

With rented campers the best charger is worthless if the customer doesn't bother to plug in the provided extension cord. The best MPPT monocrystaline solar is worthless when the customer parks it in the shade. A low cost adequate charger and a low cost adequate solar system will keep happy the customers who use it.

The low voltage disconnect that is located where the customer is unlikely to find it to bypass it can actually keep your battery cost down.

Look at a golf cart. All of the DC wiring is isolated from the chassis. If a wire chafes and wears through the insulation nothing happens. When the second wire connects to the chassis there is a problem. The regular maintenance includes using a volt meter and measure the voltage from chassis to each end of the battery. If you have any volts, some insulation has failed and must be repaired even though there is no functional problem. All those fat, finger sized battery wires have no fuses. I am not advocating fuseless campers, just making the point that what is "best" in one context might seem wrong in another context. Isolated wiring makes the first failure free but only if you do the maintenance, detect it, and fix it before the second failure. If the customer returns the camper with a blown fuse and a fan that didn't keep them cool they aren't happy. If the short was isolated, didn't blow the fuse and the fan continued to work you have a happy camper. You still have to find and correct the frayed wire.

If the camper has 120 volt wiring the green wire must connect to the chassis and the white wire must not. A ground fault circuit interruptor is a must have. Arc fault circuit interruptors will soon be must have items.

Electric trailer brakes can be isolated from the tow vehicle grounding, powered by the house battery, controller mounted in the trailer, activated by a brake light powered relay applying the brakes according to the inertia sensor in the controller. This is a defensive design for a rental camper. For your own camper you might want the controller at the dashboard.

For a rental camper there is no way an alternator connection can be counted on. Some renters might have 7 pin connectors with a perfect alternator connection. Nine out of ten won't.

Do you expect some customers to need to use a CPAP or have some other power requirement? Maybe you could have an optional higher performance system. Think of the Inergy Kodiak sort of box except it is added to your standard camper and is an affordable design.