Charging Strategy, 1994 RoadTrek

[4gnomad]

Hi all, I've been diving back into how to upgrade my battery system in my class B and was hoping someone here could sanity check me. I have a small 100AH 12V coach battery and I'm upgrading to a pair of L16s (6V, 400AH). My RT has the old MagnaTek charger, which is rated at 32A, but the charging circuit to the batteries is fused at 15A.

The L16s accept up to .25C, so they'll take up to 100A for a few hours before the current drops. I'd like to hit that target to ensure a nice long life for these bad boys and prevent sulfation. Obviously that's not going to happen over a 15A circuit. So here's what I'm thinking:

1. Hook up a Powermax or some other quality 100A charger directly to the battery. I think I can just remove the trickle charger that's in there now (and which I've never used).
2. Pull the fuse on the existing charging circuit so that circuit isn't active when I'm hooked to shore power.
3. When I hook up to shore power hook up both the charger and the regular shore power connection to whatever is available (15/30 is all my rig can handle).
4. From another post I also need to protect the circuit coming off of the alternator so I don't overcharge the AGMs if something goes wonky up front and it starts putting out too much voltage.

My main question is with regard to #3 above - anyone see any problem with me charging the battery and running off of shore power at the same time as long as I've disconnected the original charging circuit?

Last, I eventually want to add a few solar panels so I can "top off" with solar at a lower amperage after running the gennie or hooking up for a few hours to recharge. If I'm reading and understanding the charging profile correctly this is a reasonable thing to do. If I do this do I have to always remember to turn off solar charging when I hook up to shore?

[JamesJudasPries]

Yes the bus bars are great because the ones I used blue sea systems ones that are high current and are nice copper and have stainless hardware and lock-rings, so there is neglegable voltage drop.

[4gnomad]

Thanks for the photos. I was unnecessarily concerned about voltage drop across bus bars like that, but it looks like they're in pretty common use and of course really convenient. I also noticed while I was working in my coach that more of the cables are accessible than I thought, so I might be able to do more upgrades than I originally expected.

I'm going to ask one more question in the general forum about how to effectively charge my batteries and also have shore power at the same time. I think I can just split the incoming AC and plug one receptacle into the charger, one receptacle into the "shore power" cable and I should be good. Then I can buy my inverter and charger separately (I'm running into space issues with everything but the AIMS.

[JamesJudasPries]

[JamesJudasPries]

Sounds like you have it figured out.

I have never used an inverter charger combo unit, I only use a discrete converter and a cigar lighter plug in inverter.

The advantage with those inverter charger units is their high charging current ability.

I'm not sure of the ventilation and clearance requirements for those but I'm sure it says in the data paper.

Good luck with the project, I'm interested to see how it goes!

Also, here are some images of my install. One shows the under the hood solenoid, and you can almost see the fuse block at the top hidden by the other wires.

The other pic is of my bus bar setup in the electrical compartment behind my ac/dc fuse panel. Having bus bars really makes adding high current devices or add ons easy, because that way there is not a million things attached to the battery terminals. There are only two cables connecting to my batteries, in a compartment to the left you cant see in the pic. 2 GC2 batteries. The silver box is my converter. I would also recommend adding a main battery terminal type fuse so that a fault before the fuse panel, or anywhere unexpected is not going to cause a fire.

[4gnomad]

I'll definitely look into replacing the solenoid, this rig only has 70k miles but it does have a lot of years on it. And that's good information to have about the computer regulating voltage.

Right, so one power source would be:

400 AH L16s -> inverter -> 120V to coach (when I turn it on)
Battery bank charged by plugging in to shore power/genset.

The other power source would be:

94AH wet cell -> 12V to coach
Single battery charged by alternator and also by plugging in to shore power / inverter pass-through -> converter -> existing stock charging circuit

It looks like there is a Magnum Energy 2000W inverter/100A charger that might fit in the space I have available. My reading suggests that's a very trustworthy brand, but also that they've started building in China. I did read some horror stories about AIMS, but I don't know if they're current. Most of the complaints to the BBB have been resolved. Argh.

[JamesJudasPries]

Yes that sounds reasonable to me.

So I take it you will just use the new batteries with an inverter for the time being? Otherwise if you wanted to power your coach 12v system with the new batteries you will have to disconnect the existing wiring to the old coach battery and connect to the new ones, but that is likely not possible or practical till it is fully rewired/ re routed.

My camper van is a 1990 b350 dodge but not a road trek. Iv'e replaced my stock alternator with a new 120A mopar one. Its likely your replacement one is similar. This is kinda extra info, but dodge alternators are regulated by the computer which doesn't seem to run them very hard. Ultimately the computer likes to run them at 13.8 most of the time. I doubt an old 75 amp model vs a new 120 amp model would change that, but of course, the one with higher amp output would put out more current without the voltage sagging with a similar load.

My van It originally had a simple solenoid isolator, and yours likely does too.

I replaced the solenoid with a new one that is similar. They eventually rust out /burn out and fail (no longer plunge to connect/disconnect)

Luckily a Simple RV solenoid is only about 25 USD. Compare this with a BIRD which is like 200 USD. Either one will work reliably.

[4gnomad]

Thanks for the replies, I'm slowly gaining confidence in understanding the trade-offs.

1. I think the alternator on these conversions has been beefed up. That said, I haven't been able to figure out what I've got yet. It's a reman and their sticker covers the original info, so I'll need to peel that off.

2. I probably don't actually need 3000 watts. I was selecting the 3000 because it has a charger at 100A, and these 400AH L16s want C/4 in the first stage. Since I just spent $900 on these AGMs I want to make sure I don't undercharge and sulfate them.

3. That AIMS inverter gets 5 stars on Amazon. Are they known bad? If they are I'll probably go for something else. I'm glad to get this feedback because I was literally about to hit the "buy" button.

4. The whole idea is to boondock for 5-7 days at a time (in one or two locations), then pony up for full hookups at a site and recharge for 12 hours, then do it all over again. I know this is on the edge of the possible, but I'm a pretty lightweight user, and I have propane for most of my stuff if I need it (and a Honda 2000).

5. I'm thinking I'm not currently in a position to get the wiring done to upgrade the circuit coming off the alternator. And I'm not sure what kind of isolator I have at this point, but it's from 94, so it probably is the older type (I can see it, but can't quite make out a model number).

I'm planning on doing this upgrade next week, and I think I'm short on experience to do it myself (though I'm getting there, and would prefer to) and short on sufficient funds to pay someone to upgrade everything. Instead what I think I'll do for the interim (until I can upgrade the alternator/isolator and wiring) is just leave the existing 94AH house battery in place with the existing wiring and keep the inverter/charger solely connected to the 400AH bank in back. Then I can just run off the original coach battery for your basic overnights and switch to the inverter/400AH bank when I'm in one spot for several days (or need to run bigger items).

Does that sound like a reasonable solution/compromise? I know I'm giving up charging off the alternator on my big bank for the time being but it's pretty clear that this would require more extensive upgrades than I can do right now.

[JamesJudasPries]

I agree with Piano,

Its possible for the alternator to put out 120A but you must consider what the vehicle draws will be as well. Dodge charging systems of that era are lazy and indeed will likely shoot for only around 13.8 volts unless it is very cold outside. Also, I could probably guarantee that the existing charging wire is not adequate. Use #2 awg wire for your charge line. Connect it directly to the alternator positive post so that the original alternator wire lug is stacked on the lug with your new one. Attach a Fuse it as close as possible to alternator where you can access it. Fuse it at 100 amps. Do not connect the new wire on the engine battery, then you would be at the mercy of probably #6 awg OEM charging wire to the battery, which is far too small. Don't forget to add a nice big #2 wire for the L16 negative terminal to a shiny, thick spot on your frame somewhere.

I said to fuse it at 100 amps because you will likely use 105 degree C rated wire, but under the hood you will easily add even more heat. I doubt the alt will be able to blow that fuse even charging thirsty batteries with all other accessories running that are taking away some amps on the chassis side. Realistically, max charge current will probably be close to 90 amps with highway rpm and low coach batteries with the vehicle lights and fan off. Expect that figure to drop to about 40 amps or less at warm idle. With that alternator you WILL NEVER overcharge your batteries.

You would only have to worry about overcharging if you had a vehicle with a custom, high output alternator which could provide 14.5 volts at up to 150 amps or more, and you decided to go for an 8 hour drive after you had the batts fully charged with shore power over the last 2 nights.

DO NOT use a crappy diode isolator! It will drop the voltage badly in all circumstances. There would be almost zero charging at idle, and probably 50% less charging current at higher rpm. Use either a smart solenoid (BIRD) or a continuous duty RV solenoid for your positive Connection. Grease everything with a bolted connection with spark plug grease or similar dielectric after the bolts are torqued to avoid corrosion.

Use glued heat shrink on all connections, and closed ended lugs if possible. Otherwise they will corrode. It goes without saying to Disconnect negative or both negative and positive cables of your chassis and L16 batteries when wiring to avoid nasty accidental welding and burning.

[pianotuna]

4gnomad,

You are partly right and partly wrong. The question is not straight forward at all.

120 amps is correct--but there is a duty cycle. Operating the alternator above 80 amps may push it too hard, and let out the magic blue smoke. Monitor voltage closely, if it drops below 12.3 shut down the inverter *right now*. That is unless you prefer smoked alternator with your eggs and toast.

In a modern vehicle probably 35 amps are consumed by the chassis--leaving 45 amps for other uses. At night there will be less as the headlights are often energy hogs. 45 amps may sustain a load of about 450 watts from an inverter after accounting for losses.

My MPPT charge controller plays well with the alternator.

The 130 amp alternator in my RV can sustain a 1200 watt load for about 15 to 20 minutes. Then I turn off the load for 30 minutes allow the system to recover and reduce the load on the alternator.

I'd prefer to see you "aim" a little higher in quality than the aims (which makes a bad door stop and is not repairable).

Is there some reason you MUST have 3000 watts?

To feed a 3000 watt inverter means having 6 to 7 thousand watts of battery bank (600 amp-hours). AGM 12 volt jars may be a better choice than 6 volt units, for such a large inverter.

[4gnomad]

I think I've got this pretty much figured out, but I have a question that is probably pretty straightforward for someone who isn't totally new to this stuff:

It looks like the stock alternator on the 1994 RT is 120A. The documentation from the battery manufacturer (Vision, chinese brand) says that initial charge current is also 120A. That's perfect, right?

It seems like the right solution is, like you guys said:

1. A charger inverter (thinking AIMS Power PICOGLF30W12V120VR 3000 Watt) and just run everything in the coach from the inverter
2. To run the alternator charge line directly to the battery (and not worry about overcharging because the set point for the voltage won't cause problems, especially after the drop through the isolator)
3. To run MPPT solar directly to the battery as well (since it will turn itself off when it sees the charger charging) should I want this in a future purchase

And it seems like I can switch between 120VAC and 12V systems just by turning my inverter on or off (turning it on will start inverting to 120VAC and the existing converter won't hit the batteries directly, turning it off will show no voltage from "shore power" so the batteries will be hit directly).

Unless I'm wrong, of course. 🙂

[4gnomad]

Okay, I think I have some more clarity on this. I was worried about multiple charging systems overcharging the battery (they're AGM and I'd prefer not to die in a fire), but if I get a 100A charger/inverter kit I should be good on getting enough current to the batteries for optimal charging, and if I get an MPPT solar controller it will be smart enough to see a high voltage already being applied to the batteries and turn itself off. I think I could literally connect the MPPT output to the output terminals of the charger and it would all play nicely.

Seems like the main thing to worry about is the draw on the alternator, looking into that now.

[4gnomad]

Thanks for the responses, really useful. Time to go do more research to figure this out, especially on the battery monitoring system - I really want the power systems to play nice with each other and to be idiot-proof. I hadn't considered the draw off the alternator as being a lot more substantial with the larger bank and was hoping to avoid rewiring (not something I'm comfortable doing myself).

My usage profile is more on the low daily AH usage, boondocking end. Just run a laptop, fantastic fan and some lights, so the idea is to get something like a week at a time, then go hook up somewhere overnight for a full charge. Since you're saying to get a full charge every 7-10 cycles, and I'm hoping to get a week per cycle (and I'm going to do this full time) I think that means I'll need a full charge every two months. That's totally manageable. Kind of perfect, actually.

I do think I'll leave the existing MagnaTek in there - I hate to get into it and need to rewire everything. If I just pull the fuse on the charging circuit I can't see how leaving it in would create any problems, right?

Going to research shunt based battery monitor systems now. Thanks for the tip(s), both of you.

[booster]

4gnomad wrote:
Hi all, I've been diving back into how to upgrade my battery system in my class B and was hoping someone here could sanity check me. I have a small 100AH 12V coach battery and I'm upgrading to a pair of L16s (6V, 400AH). My RT has the old MagnaTek charger, which is rated at 32A, but the charging circuit to the batteries is fused at 15A.

The L16s accept up to .25C, so they'll take up to 100A for a few hours before the current drops. I'd like to hit that target to ensure a nice long life for these bad boys and prevent sulfation. Obviously that's not going to happen over a 15A circuit. So here's what I'm thinking:

1. Hook up a Powermax or some other quality 100A charger directly to the battery. I think I can just remove the trickle charger that's in there now (and which I've never used).
2. Pull the fuse on the existing charging circuit so that circuit isn't active when I'm hooked to shore power.
3. When I hook up to shore power hook up both the charger and the regular shore power connection to whatever is available (15/30 is all my rig can handle).
4. From another post I also need to protect the circuit coming off of the alternator so I don't overcharge the AGMs if something goes wonky up front and it starts putting out too much voltage.

My main question is with regard to #3 above - anyone see any problem with me charging the battery and running off of shore power at the same time as long as I've disconnected the original charging circuit?

Last, I eventually want to add a few solar panels so I can "top off" with solar at a lower amperage after running the gennie or hooking up for a few hours to recharge. If I'm reading and understanding the charging profile correctly this is a reasonable thing to do. If I do this do I have to always remember to turn off solar charging when I hook up to shore?

Interesting project. We have 440ah of Lifeline GC2 six volt batteries in our 07 Roadtrek 190.

The first question would be if you are getting the big batteries because you want long time low load off grid capability, or because you want to run high load things through an inverter? If you are going to have a big inverter, the mentioned inverter/charger combination would probably be the best choice, as it will be less wiring and space, plus you get an internal transfer switch. You would also need another auto transfer switch upstream to switch between shore power and generator. If you already have a built in generator, that transfer switch would probably already be there.

I would get rid of the old stuff. Trying to run two chargers is going to be more trouble than it is worth. The original is old and probably dirty power besides.

Your alternator in a 1994 may only be running at 13.8 volts or so, which is very safe for charging, but slow. If you have an isolator, that will also drop you .7 volts. The Lifelines will like 14.3v for charging, but you would need to have a disconnect to prevent overcharging. You will also likely need to upgrade the wiring to the coach from the engine, as those batteries will accept way more amps than you current wiring will handle. You could also fry a stock style alternator, as they don't like to run at full output. Per Lifeline, our batteries will pull near 400 amps for the first 10 minutes and settle at near 300 amps until it starts to taper, so you need to have power sources that can run at full output without damage and they will give the current limiting. Remote regulators can be used on an alternator to limit it's output to make it survive, also.

Our Lifelines require over 8 hours of time to get totally full from an over 50% discharge (100 amp charger), so you may be underestimating the time it will take to recharge. The current will start to taper by 70% full and the last 5% can take nearly as much time as the entire rest of the cycle. To take good care of the batteries they need to get totally full every 7-10 charge cycles, and the only good way to know if you are full is with a shunt based battery monitor system. Some of the nicer inverter/chargers have a monitor option built into the remote, which is a clean way to go.

Solar is good way to help at the end of a charge cycle, once the acceptance amps go down far enough. Unfortunately, it does take a lot of time to get the batteries full, so the other sources would need to get you to the solar's capacity quickly, as you might need 6 or more hours of good sun to fully top the last bit of charge. The more solar you have, the sooner you can shut off the other sources like the generator or engine. We have 300 watts. If you get a decent solar controller, it can run off the same battery shunt as the battery monitor does. It should take care of itself without any intervention needed in relation to the other charging sources.

[pianotuna]

15 amp shore power with a power factor corrected charger will output up to 125 amps @ 12 volts (nominal).

If you have plans for using an inverter you could go to an inverter/charger and use that for high rate charging.

I simply unplugged the OEM converter from 120 volt supply and left it in place as a back up.