charging rates

pianotuna wrote:
I thought that might be because I had a flooded marine battery (from 2005) for the starter. I finally replaced that in 2017 in the spring with a AGM. I still get almost no charging for the house bank.

Don, perhaps your motorhome's engine alternator/engine battery/coach batteries interconnection system is different than my Itasca's.

I have two voltmeters and an ammeter mounted on the cab dash. One voltmeter shows the voltage on the engine's 12 volt system, the other voltmeter shows the voltage on the coach's 12 volt outlets, and the ammeter has it's shunt mounted in the main coach batteries' negative cable connected to the chassis frame.

The two voltmeters read within about 1/10 volt of each other all the time whenever the engine is running -> if and only if the interconnect solenoid (that activates from the ignition key) is activated AND has contacts in good conditon ... such that there is no resistance voltage drop across it's contacts (I've had to change it twice in 11 years).

As I drive down the road, both of the voltmeters track each other and slowly drop in voltage reading as the coach batteries charge up while driving. The ammeter drops down to near zero within a few hours of driving after camping - thus indicating that the coach batteries are no longer accepting charge current at whatever voltage the meters indicate.

This behavior leads me to believe that Winnebago has the engine battery and coach batteries wired in parallel with each other someway. Since the engine battery is liquid acid and the coach batteries are AGM, they're all getting charged together at the same voltage from the alternator, as indicated by the voltmeters. However as the coach batteries run down when drycamping, of course the engine battery doesn't run down - so the three batteries aren't in "hardwire/direct" parallel with each other ... BUT there is not a diode drop difference in the readings on the two voltmeters, so the engine and coach batteries are not isolated by simple diodes. Maybe there is some computer control of the engine battery charging that is separate, even though my two voltmeters show near identical voltage readings from the systems (engine 12V system and RV 12V system).

Whatever is going on it all plays together perfectly, even with mixed battery technologies. However the coach/engine batteries interconnect solenoid must have good contact surfaces for my situation. I wonder how many of these solenoids in RVs everywhere are activating all right, but introduce a voltage drop across there contacts after a few years with the RV owners not even aware of it. What this does is cause the coach batteries to never get charged adequately between campsites. The coach batteries are getting some charge, but not enough because of the reduced charging voltage on their terminals due to the voltage drop from the alternator created by the drop across the interconnect solenoid's contacts.

pianotuna wrote:
If you MUST get an amp-hour counter use the Victron or the Smartgauge.

I have a Victron. I also have that backed up by a Simpson analog meter and a handheld Fluke that I use for calibration. All three meters measure within .05 VDC. The Victron is easy to install and takes up little space. A complete hardware mounting kit is included with the meter.

The OP's weak spot will be the small capacity of two BCI 27 series batteries. If two 6V GC2 can be installed in their place (typically, a two hour job), the OP would have twice the battery capacity and shouldn't have a worry after.

Phil,

My house bank charging path is twin #8 wires with manually controlled solenoids.

When I had flooded jars I got good charging. Once I moved to AGM telcom jars I found that after a day in the sun the house batteries would flow current to the engine and that I would only see charging when I put the system under a large load such as running the water heater on electric.

I thought that might be because I had a flooded marine battery (from 2005) for the starter. I finally replaced that in 2017 in the spring with a AGM. I still get almost no charging for the house bank.

I surmise the reason is because the telcom jars float at a higher number than the flooded units.

If you MUST get an amp-hour counter use the Victron or the Smartgauge.

To Phil's question, I have 14.5 v at D.C. Connection with engine running so charging system appears to be working. We have trip coming up soon so will probably not get a battery monitor installed but that is definitely on the schedule.

Thanks again to all of you who took the time to address my questions. The advice was great and I have learned a lot.

Countrykids. I stand by my 4-5 hour recharge time. But next time you need new batteries look at the GC-2 6 volt recommended by another poster.

YOur wire size is fine, everything is good, just go and enjoy. You do not have to run the generator while on the road to charge the batteries. I camp sans electric on the beach and in national forests extensively and it all works out fine.

countrykids wrote:
Main points learned are that alternator is likely to be quite slow and that it's OK to use the generator while traveling. I'll just experiment to see when I need the generator and when not.

In your 2004 Class C that probably is built on a Ford E350 or Ford E450 chassis, you should not need to run your generator while going down the road to charge your motorhome's batteries between campsites that are at least 3-4 hours driving time apart. If your chassis is a Ford E350 or E450, it probably has a 120 amp or 130 amp alternator in it. This size alternator is more than enough to take care of your motorhome's batteries between campities most of the time when underway.

For instance we have two Group 31 12 volt batteries in our 2005 Class C - and even when IDLING, the Ford alternator has supplied 70 amps into those two batteries to charge them. When traveling between campsites a few hours, the alternator has way more capacity than when idling and so can charge the batteries all the way up to where they are only taking 1 amp or less.

It's very important that you have a voltmeter plugged into a 12 volt socket back in your motorhome then check it quickly with the V10 engine running, before starting out down the road. If this voltmeter DOES NOT read 14 or more volts before you start out, then something is wrong with your charging circuit going from the alternator back to the motorhome's batteries. If so, this problem should be addressed - instead of having to run the generator all the time between campsites.

countrykids wrote:
Matt,

What do you have as a meter? I do the voltage thing now and as you pointed out it's pretty iffy.

There are two good ones that I know of, one is from Bogart engineering and the other from Victron Energy. If you google both of those, you will see what I mean. Both companies make very good products both require that you install a shunt to measure the DC current coming and going.

Study both, I would recommend, but I have not been following the market for some time. When you decide, shop around on the web as prices can vary and be sure the shunt is included.

When you get this, you will love it. It will keep you informed as the state of your house bank all the time.

Matt

Mr Wizard is one of the best folks to speak with about things electrical. But even Univac made mistakes. The difference is that he "owns up" to such errors instead of sweeping them under the rug. Take his advice--it is 99.9% correct.

"Depends on the size of the wire between the battery isolator and the batteries"

This IS the right answer from MrWizard and along with the tow vehicle/vehicle alternator's amperage output available. Can't get the needed amps to the batteries either unless the alternator produces them! Then the biggie, a wiring circuit's wires diameter determines how many amps it will or can carry thru it and the smallest diameter wire or connection at any point in the entire circiut is an acting CHOKE which controls how many amps get thru.

That is why I have #2 gauge fine strand copper welder cable going from my dual alternators all the way back to the battery bank in the 5th wheel with 80 amp marine slow blow fuses and a slide switch under the tow vehicle hood and a marine very HDbarrel switch on the 5th wheel. 12V DC has lots of line loss thru long length wires barely capable of the rated amps in just a foot long wire. Having 12V DC in a vehicle/RV battery system is why you need a much larger diameter wire to avoid so much loss all the way from the alternator final output connection all the way to the batteries.

Larger wires carry more amps/volts with considerably less resistance loss! Simple, you don't use a 13 amp 16 gauge extension cord in your home to run a 15 or more amp draw load unless you want a fire to extinguish. So why do it in your RV's 12 V DC charging system with wires that can't transport the electrons wanted? Also not smart to use 1/4" ID diameter hose to a rainbird sprinkler and expect it to bring enough water to make the rainbird do its job!