Battery Charging Issues

[TJLee089]

Battery Charging Issues

Advice requested!

I have a 2013 Itasca Reyo which I bought new earlier this year. It has an Onan 3.6K generator and two Napa 8042 deep cycle batteries, reserve capacity 120 minutes, which I calculate to 50 amp-hr each (120/60 X 25 = 50). While on a 5 day "boondock," I find running the generator 1-2 hr/day is not enough. I do use the the 120v TV evenings, estimated at 90 watts (Xantrex xm1000 1000 watt inverter).

My battery "charger" is a Mity-Mite RVCDP55 power center, output: 13 vdc, 55 amps. Actual voltage while charging is 13.2-13.4 volts. The battery voltage after this charging scenario is usually about 12.1-12.3 volts, or 50-70% of capacity.

I have learned that my converter/charger at 13.2 volts is really a "float" charger (as with most motor homes) that realistically will never fully charge the batteries in a limited time.

Here are the options I am considering. Any advice is welcome.

1. Live with the situation. Fully charge the batteries at home with "shore" power.

2. Replace the Mity-Mite converter charger with a multistage charger unit. Since the Mity-Mite power center includes AC breakers and DC fuses, this option is not appealing.

3. Run the engine to "top off" the batteries. The engine produces 13.9 volts. I don't know how long this would take, but I am sure it would be fuel inefficient.

4. Replace the batteries with higher capacity ones. I will almost certainly do this at the end of their life but hesitate to do this now, not knowing how much I would actually gain.

5. Buy a separate multi-stage charger to run off the generator and charge the batteries faster and closer to full charge. I suspect such a device would be expensive.

6. Carry a small generator (500-1000 watts) to charge the batteries. I would need to also carry gasoline. Not an attractive option.

7. Install solar panels. I don't do enough boondocking to justify the cost.

I am leaning to either option 1, 3, or 5. Any advice would be appreciated.

 

[Graphite Dave]

Solar is a viable option. For around $500 plus your free labor you can install 200 watt panel with a Morningstar Sunsaver MPPT controller. That way you get correct charging with very little operator interface. No need to change the existing system. You do need to be sure you are in a climate that works for solar.

 

[jackfish]

If the converter/charger is 13.2 volts and the alternator is 13.9 volts, nothing you have will fully charge your batteries, even plugged into shore power or running the generator. It is unfortunate that RV manufacturers design and build systems that are not competent.
A Magnum MMS1012 with a ME-RC50 remote would replace both your inverter and converter and give you a three stage, temperature compensated, charger than can be set to your batteries' charging requirements, and a 1000 watt pure sine wave inverter in one unit. Both your generator and shore power would then appropriately charge your batteries through the MMS1012.
You will eventually replace those batteries, and true deep cycle batteries should be the only choice. Not any battery that has only a cranking/starting specification even though it is called deep cycle. If it doesn't have a 20 hour amp hour rating, forget it.

 

[Graphite Dave]

I have the Magnum MSS 1012 and the ME-RC Remote with the ME-BMK shunt and am very satisfied with that combination. You will then get correct 3 stage charging that is matched to your battery size and type.

 

[jackfish]

I forgot to add that you can probably bypass the Mity-Mite converter and connect right into the breaker/fuse panel. So the converter would be disconnected but the panel could still be used. Might have to install an 120 V AC subpanel as well.

 

[TJLee089]

"If the converter/charger is 13.2 volts and the alternator is 13.9 volts, nothing you have will fully charge your batteries, even plugged into shore power or running the generator."

I agree. This makes me lean toward a stand alone multi-stage charger.

Although the Magnum MMS1012 with a ME-RC50 remote option is tempting, I would probably not want to tackle this myself. Any independents that would do this? I doubt an Itasca dealer would touch this. Thanks in advance.

 

[rb3232]

Battery Charging Issues
snip>

3. Run the engine to "top off" the batteries. The engine produces 13.9 volts. " snip

The engine produces 13.9 volts... hmm where did you measure? I think the alternator voltage should be 14.2V, check for loss between alternator and battery.

 

[segler]

The absolutely first thing you should do is get a good battery monitor. Otherwise, you are flying blind. You didn't say anything in your OP about this.

So, I would recommend the Trimetric 2025. There are a couple other good ones out there, but I have had excellent luck with the Trimetric, as have many others.

The Trimetric, with its included shunt, displays current, voltage, and it calculates battery state of charge by means of current times time, rather than voltage.

 

[TJLee089]

The engine produces 13.9 volts... hmm where did you measure? I think the alternator voltage should be 14.2V, check for loss between alternator and battery.

Per the RV monitor panel. I assume the drop is due to line loss from the alternator to the panel.

 

[TJLee089]

The absolutely first thing you should do is get a good battery monitor. Otherwise, you are flying blind. You didn't say anything in your OP about this.

So, I would recommend the Trimetric 2025. There are a couple other good ones out there, but I have had excellent luck with the Trimetric, as have many others.

The Trimetric, with its included shunt, displays current, voltage, and it calculates battery state of charge by means of current times time, rather than voltage.

The Itasca Reyo includes the One Place Systems Center (see http://media.goitasca.com/models/gallery/jpg/wb_50456609_RE-OnePlace-13.jpg). I will look into the Trimetric, but regardless, it's clear that neither the converter/charger nor the engine alternator produce sufficient voltage to fully charge the batteries. The battery monitor doesn't address that.

 

[rb3232]

The Itasca Reyo includes the One Place Systems Center (see http://media.goitasca.com/models/gallery/jpg/wb_50456609_RE-OnePlace-13.jpg). I will look into the Trimetric, but regardless, it's clear that neither the converter/charger nor the engine alternator produce sufficient voltage to fully charge the batteries. The battery monitor doesn't address that.

I will only speak to the alternator issue:
Your alternator does or should produce sufficient voltage. You need to figure out if the full alternator output voltage (14.2V I think) is getting to the battery (measure at the battery) and if not why. Then correct the problem.

 

[TJLee089]

I will be driving for 4+ hours tomorrow and will see what the battery voltage is at the end of that time. I will also check at home with VOM with engine running. Still need to address charging via generator. Thanks.

 

[jackfish]

Using a multimeter with the probes at the battery terminals while the engine is running should give you an accurate reading of alternator voltage to the batteries. Should be about 14.2 volts reading at that location. Your One Place Systems Center may not be expected to give an accurate battery voltage reading. In addition, 14.2 volts from the alternator is not enough to do a bulk charge to fully charge most batteries, especially if they are substantially discharged.

 

[TJLee089]

Just returned home after driving 4+ hours. Disconnected DC main from house batteries (open circuit). Voltage 13.24 at each battery. One Place Systems Center (DC main closed) showed 13.1v. Later 13.08v (open circuit). 4+ hours later, 13.01v (open circuit). It is clear that the vehicle alternator CAN fully charge the house batteries. Now to further investigate why the genset cannot and what can be done. Probably it's simply the low output voltage from the converter/charger. Thanks to all.

 

[TJLee089]

Following the suggestion of Segler, I looked into battery monitors, comparing the Trimetric 2015, the Xantrex LinkLite, and the Victron BMV 600S. I went with the Victron, $158 on EBay. Why? Price includes modular UTP cable - no messing with preparing wires! The only thing I had to provide was the cable between the battery and the shunt. Installation is simple EXCEPT for snaking the UTP cable from the battery compartment to the mounted display. I had to drill one hole in the floor under a cabinet and learned a lot about removing panels, drawers, etc. The Victron manual can be a bit overwhelming but the only parameter you really need to set is the battery bank capacity. I have 2 (OEM) Napa 8240 batteries. The only info I can find on the NAPA site is reserve capacity at 120 minutes. Since reserve capacity is defined at 25 amps, this comes to 50 Ah each, 100 Ah total. This is probably conservative (low) since draw would normally be much less than 25 amps.

One "bug" I did find after setup was a 0.31 amp draw even with the DC main off. I finally found the section in the manual about "zeroing" the current reading with the negative cables disconnected from the shunt. This worked OK. This section in the manual is "hidden" within a section about using alternative shunts.

All in all, I 'm happy with the Victron thus far. At home, I keep my rig connected to AC with a timer on 1 hour per day. I need to keep the DC main on to charge during that one hour with my converter/charger. With the AC off and the DC on, draw is 0.85 amps. I don't think I can easily do much about that. This is about 20 Ah, or 20% of bank capacity, until the next 1 hour charge. Can I input 20 Ah on a 1 hour charge? I'll find out and let you know.

 

[TJLee089]

I'll cut to the chase. First of all, there is no way the Mity-Mite converter charger can replace 20Ah in one hour since the output voltage is only about 13.2.

I went ahead and replaced the OEM Xantrex Pro XM 1000 inverter with a Xantrex HF 1055 inverter/charger, a 3 stage charger. This was "almost" a drop-in installation since the AC, DC, and signal cables and monitor opening are the same for both. The HF 1055 is larger but it did fit in the same spot.

The charger does its thing whenever shore power is connected. If shore power is turned off, e.g. via timer, the inverter remains on drawing about 0.78A even with no AC load. The logic would be to continue AC power when shore power is lost, however it would be nice to have a mode where the inverter would be off when shore power is off to allow a timer to be used to keep the batteries charge when in storage.

The HF 1055 seems to meet my objective. Starting with a battery about 20% down at -16.5Ah (C20 estimated at 80Ah), I was able to get to to float (-3.9Ah) in about an hour. The bulk stage (~50A) lasted only a minute or so. In 2 minutes the current was 34A; in 8 min, 24A, in 20 min 11.2A.

One issue puzzles me a bit. Various sources indicate an FLA battery should not be charged at a current of more than 10-15% of the battery C20 rating (10-15A for a 100Ah battery). The HF 1055 has 4 selectable maximum current settings: 5, 15, 35, 55A.

I used the maximum 55A setting and got the charge current as indicated above. I frequently felt the battery cases and did not notice any warmth. Is this a mistake to allow the batteries to charge as fast as possible? If I were starting at 50% SOC, obviously the bulk stage would last much longer and generate more heat from a higher current.

I welcome your comments.

 

[calbiker]

I think charging at 55A is too high. You can tell the batteries don't like it as they accept 55A for only second. What does the battery spec say?

However, it could be the cable. How big is the charging cable. What length? You probably could use ott gauge.

Cal

 

[TJLee089]

I think charging at 55A is too high. You can tell the batteries don't like it as they accept 55A for only second. What does the battery spec say?

However, it could be the cable. How big is the charging cable. What length? You probably could use ott gauge.

Cal

Since the inverter is rated at 1000 watts (83 amps at 12 volts), I'm confident the cables are big enough. I suspect the bulk charge time was very short because the battery was already at about 80% charged. There is almost no useful info available for the (OEM) NAPA 8240 batteries. No idea what an ott gage is. "Rule of Thumb" I should only use the 15 amp charge rate. Am I correct that the main symptom of too high a charge current would be a warm/hot battery and liquid loss? My RV is now in winter storage, so no more experimenting for now. Thanks for the feedback.

 

[icarus]

What you really need is a proper deep cycle 4 stage charger. The Mighty mite is simply an automotive charger. Deep cycle batteries need a proper charge regimen including bulk, absorb, float and Eq charge capability.

I suggest you read the following links:http://www.batteryfaq.org/

http://www.solar-electric.com/deep-cycle-battery-faq.html

Icarus

 

[TJLee089]

What you really need is a proper deep cycle 4 stage charger. The Mighty mite is simply an automotive charger. Deep cycle batteries need a proper charge regimen including bulk, absorb, float and Eq charge capability.

I suggest you read the following links:http://www.batteryfaq.org/

http://www.solar-electric.com/deep-cycle-battery-faq.html

Icarus

You missed the point that I have a newly installed Xantrex HF 1055 inverter/charger (3 stage). The MityMite has nothing to do with this.