battery charging question

[JohnEd]

Hope Sean is listening/... and others.

Is there any reason I can't run off of my batteries WHILE the charger is charging?  After they are fully charged?  I want to bypass my converter.

Thanks.

John

[Lin]

John,

Do I have this right?  Instead of using a converter, you want the battery charger to be continually on while you are plugged in.  The idea being that as you use 12volt loads, the charger will keep the batteries up.  If that is what you want, it can be done with the proper charger.  That is exactly what inverter/chargers do so one would not need a converter at all.  As far as I understand though, you would need a multi-stage charger that would not attempt to overcharge the bank.  I do that with my Trace inverter.  There is a converter in the bus too which I will wire around an remove eventually, but I leave it unplugged for now and have disabled the charger in it anyway.

[redbus]

John

I know people that have used a small battery charger for years in place of a converter. Basically all a converter does is run as a filtered charger so you might get some electrical interference but it will work.

[TomC]

I use my Trace inverter/charger as my only plugged in charger.  My bus is plugged in all the time.  I do notice that my Fantastic vents make a high pitched whine when on the charger, but that's the only thing I have noticed.  Good Luck, TomC

[Lin]

The type of batteries you have is important in relation to the capabilities of the charger too.  I ruined a whole bank of AGM batteries by being plugged in long term to a 3-stage charger that did not go low enough.  My Trace inverter/charger now is adjustable so I can set it to the battery manufacturer's specs.

[Sean]

Hope Sean is listening ...

Yes  

Is there any reason I can't run off of my batteries WHILE the charger is charging?  After they are fully charged?  I want to bypass my converter.

Well, like Tom, we have no converter, only the high-quality charger built into our Xantrex SW402.  So, yes, it can be done.

That said, you should be aware that, like everything, there are pros and cons.

A converter has a battery charger built into it, as well as a 12vdc power supply (more on this in a moment).  Usually, the battery charger is very low quality, probably single-stage or at most two stages, and not adjustable.  So they are not very friendly to batteries, and I dislike them for this reason.  Beside that, if you already have another charger anyway, the converter's charger is redundant, or worse, could be interfering with a different higher-quality charger's ability to do the job.

A high-quality charger, OTOH, will have at least three charging "stages," known as Bulk, Absorption, and Float, and will often be user-adjustable, meaning you get to set the voltage and/or current parameters for each stage.

The problem with running your DC lights and appliances when such a charger is connected has to do with voltage.  Typical maximum Bulk stage voltage settings are 14.4v for 12-volt (nominal) systems, and 28.8v for 24-volt systems.  The voltage will start out much lower than this, but will rise to this value as the Bulk stage nears completion, then remain at this value for the duration of the Absorption stage.  When the Absorption stage is finished (usually, this is a user-settable time period, typically 1-2 hours), only then will the voltage drop to the "Float" setting, typically 13.3v or so for 12-volt systems, or 26.6 or so for 24-volt systems.

Most light bulbs designed for 12-v nominal systems are made to handle voltages up to 14.5-15 volts, and the same is even more true for other 12-v appliances.  The same reasoning applies to 24-v systems, where components are typically tested at 28-29 volts.  But a lamp will have a longer lifespan on 12-13 volts then it will on 14.5 volts, so running your 12- or 24-volt nominal devices on charger current may shorten their lifespan.

Now having said that, I will tell you that we have lived on our bus full-time for six years, and in all that time we have replaced a total of two (24-volt) light bulbs.  Our bulk voltage setting is 28.8 and our float setting is 26.8.  We even have an equalize setting of 29.8v (and it used to be 30 volts) with an equalize period of one hour, and even that has not damaged any lamps or appliances.  Our Vanner equalizer divides this number exactly in half at all times, and that's what is fed to our handful of 12-volt appliances, such as fans, LP detector, the litter box, the wireless router, etc., and none of those has had any issues up to 15 volts.

Keeping use of lights in particular, and anything you think might be sensitive to high voltage, to a minimum during the Bulk and Absorption stages can minimize the risk and any long-term effects on equipment longevity.

Long-winded answer, I know.

... Basically all a converter does is run as a filtered charger ...

This is not entirely correct.

The principal distinguishing feature of a converter (versus a regular charger, filtered or not) is that it has a heavy-duty disconnect solenoid between the batteries and the loads.  The solenoid is "normally closed," meaning the loads are normally connected to the batteries when the converter is not energized.

As soon as the converter begins receiving 120 vac at its input, it energizes a 12 vdc power supply, and the loads are switched to this power supply, then disconnected from the batteries.  Usually this is accomplished with a double-throw relay, with the load on the common pole, the batteries on the N/C pole, and the power supply on the N/O pole.

Once this is done, the battery charger is brought on line and connected to the batteries.  What this does is allow the battery charger to charge at, say, 14 volts, while the loads are powered at a regulated 12 or 12.5 volts (or whatever that particular converter's setting is).

"High quality" converters (which, IMO, is almost an oxymoron) will actually have a separate charger and power supply, so that the state of charge of the batteries and how hard the charger has to work will have no impact on the voltage provided to the loads by the power supply.  Lower quality converters may combine some of the AC/DC conversion hardware between the charger and supply, and the loads may experience ripple effects from the charger cycling on and off or providing more or less current.  The cheapest units use the same DC supply for the charger and the loads, with the latter receiving a fixed percentage of the voltage of the former; these units have single-stage, single-voltage chargers, well-known for cooking batteries if left on too long.

Because of the separation of loads from the batteries during converter operation, a converter can work to power your DC loads even when the batteries are removed from the coach.  By contrast, a regular charger should never be operated with the batteries disconnected (you could damage the charger, the loads, or both) and so you will have no DC power available when the batteries are out.  High quality inverter/chargers such as the Xantrex SW series will not even come on line unless they first detect battery voltage present on the DC input.

HTH,

-Sean
http://OurOdyssey.BlogSpot.com

[JohnEd]

The converter charger in my S&S has a charger built into it.  Not much but a card that puts out 10 amps and I don't know if it is three stage.  The way the thing works is that it connects the bats to the dc bus when there is no AC.  When I hit the AC breaker, the DC path from the bat is interupted and the dc bus is switched over to the converter output.  The converter simultaniosly connects the bats to the charger.  They spent a lot of money making sure the thing worked in a complicated manner.  One benefit of their way is that the DC from the converter is about 16 volts and all my stuff, from lights to motors runs at quick time.  It is connected like yours cause it is patched and I think I will keep it that way as replacing that converter will cost big time.

I have screwed up so many bats it isn't even fit data to share.  Thank God for those really extended warranties that I paid extra for.

Thanks all,

John

[JohnEd]

And thanks to Sean I will now repair that 30 amp converter.  At one time I had a three stage bat charger wired through the converter and hooked to the built in crummy charger so it worked like it was designed but used my charger.  I didn't arrive at this design through careful analysis and design but rather as a work around a 7 amp charger failure that was going to cost me $80 to repair and I installed a 20 amp charger for $25.  I know I look smart but that ain't really the case in this case.

I have a NIB 30 amp converter bought from Dick Wright that I will sell for 75%.....hopefully.  You like?

John

[pvcces]

Sean, you bring a lot of clarity to these issues. Thanks.

Tom Caffrey