Somewhat different V3 use

[Lever]

I am very glad to be able to sign up for the forum without being a product owner, yet.

I am working on a couple of setups for small, class b (van based) RVs, which are quickly moving toward big battery banks and very large alternators on the van engine. The trend is to eliminate the onboard generators in most cases. The alternators can be parallel to the existing setup, if the vehicle computer is OK with that (Sprinters are not), or as a standalone connected only to the coach batteries.

I am looking at doing our system first, which would be a combined setup with two alternators on the Chevy 6.0 gas engine. The V3 regulator looks to be our best option because we do all our battery charging control based on amps to the batteries to transition to float. We have 440ah of Lifeline GC2 batteries, and Lifeline recommends .5% of capacity to transition, so we go to float at 2 amps at absorption voltage. We have an ammeter on the dash that we can watch to see the transition point coming. The V3 can be held in absorption of a dash switch, so that is perfect for us, as we will just lock it in and then unlock it when we get to 2 amps to the batteries. It also has battery temp compensation, so that is good for us as we will be charging at high rates for rapid recovery of partial charges.

What is an issue, I think, is that there is no alternator temp sensors with the V3, as they appear to be designed to run with 100% duty cycle alternators, which makes a lot of sense. Unfortunately, we already have the dual mounts for two Chevy style alternators and one 250 amp Denso style (DC power) alternator (they are very good at idle and when hot) so getting two new alternators would put us out of budget by a long ways.

The current plan would be to get a second, identical, 250 amp alternator, with both setup for remote regulation with the V3, running parallel as the V3 is said to be able to run two fields. The alternator folks say we should be able to get at least 150 amps apiece out of the alternators without overheating, but don't recommend a setup without alternator temp sensing. I think we would be looking at setting up two current limit points on toggle switches. The first would be at something like 260 amps and would be used for getting a quick recovery of maybe 100 amp hours if sun is bad so the solar can't keep up. A 30 minute run could get us two days of power. The second limit would be for when we would have a longer drive to get the batteries back to full and would be in the 200 amp range. We may have to back off on either or both of these limits if the batteries get too hot, though.

Has anyone tried to run a manual system of this type? I couldn't find anything much like it in the other areas of the forum. I does seem that the RV stuff is different than the marine applications, at least when moving, as we would have access to manually control very easily as we drive.

I appreciate any guidance anyone may have.

[Coulomb]

Dual current limits are common small boats with small engines. If power for propulsion is needed then limit the current to a lower value and open it up otherwise.

The original hot rating was for alternators approved for use in ambulances where they had to be able to produce full output at 200F air temperature. Most applications will not reach that temperature, so sensing alternator temperature is only required for automotive alternators. For instance, one of our vehicles, on a very hot day is happy powering the A/C fan on high -- just don't turn on the headlights or the diodes will short.

Many large frame alternators, especially if used on trucks, will operate well in temperatures that the engine can operate in.

You have 440 Ah of batteries. We'd guess that about 40 of those were added after manufacturing as the batteries passed through the marketing department on the way to the shipping dock.

There is a rule of thumb called the Ampere Hour law that provides guidance about
battery acceptance rate. It's exponential but basically says that the acceptance
rate at the onset of charge is equal to the amp-hours depleted. For a 50%
discharge, that would be about 200 Amps, and that will decline rapidly.
Anything not absorbed by the battery is dissipated as heat in the battery.

The design considerations given in the Primer, http://www.amplepower.com/primer/consider/index.html, call for an alternator of 100 to 160A for the size bank you have.

[Lever]

Thanks for the quick reply, I appreciate it.

I think that our setup may be closer to an automotive than truck setup. It is is a full size Chevy Express van running just about at maximum weight of 9600#. The engine compartment if very tight on the vans compared to the pickups, and the vans will overheat much more easily on long climbs or towing. In a setup that is installed in a Sprinter as a standalone extra alternator for just the coach, I recently saw a charging current graph that showed the alternator going into thermal reduction and cycling in about 10 minutes and continuing the up and down for over an hour after that. The system was a DC Power 270XP alternator with a Balmar regulator doing the temp sensing on it. That system only netted about 160 amp hours the first hour due to the cycling. The DC Power alternators are used a lot in the RVs, probably because there are mounting kits available and they have very high output at idle compared to most other alternators. In many respects his 270 amp alternator is behaving like a 160 amp 100% duty cycle unit.

Interesting about the magical extra 40ah showing up. We haven't done a full drawdown test of ours, as it just can't be all that good for them to go that far down. I have taken them down to 20% state of charge (based on the 440ah and at 20hr rate) and the rested voltage did check a bit above what Lifeline said they should be at 20%. We use a shunt based monitor system on both our solar and shore chargers, so we have very accurate amp hour usage information.

Is the Ampere Hour Law for any particular battery style? It does seem to fit fairly closely to the information I got from Lifeline about our setup. At 350 amp hours down, they said to expect about 360 amps of acceptance, and when I look at the approximate amps over time they gave it is pretty close to the amount of amp hours left to return at that point. I think this will be very useful for us, thanks.

I have looked at the Primer, and saw the low-mid 100s of amps recommendation. I can't disagree with it at all from a practical point, and I am certain it would work well. Unfortunately, the small RV world is playing to a different set of requirements (desires?) Many are now trying to go all electric for the coach, usually with diesel used for heat and hot water. They also want to ditch the 110 volt 2800 watt generators that have been used in most of them in the past. With 2000 watt induction cooktops, 1500 watt toaster ovens, and huge Keurig coffee makers, they use a lot of power for cooking. There are also large TV/sound systems and such. They usually are using 3000 watt or larger inverters. It is not unusual for these units to use 100-300 amp hours per day, and that is without trying to run the air conditioning off the batteries for short periods, usually to prevent baking the pets while the owners are gone for a while.

Since RVs don't usually motor somewhere every day, they can quickly run out of power because of the above, so they want to have a very quick recovery method to get battery capacity back. That is where the desire for much larger than 160 amps of charging comes in, and nearly all of the latest systems are using the 270 amp alternators that give well over 100 amps at idle. If people are doing air conditioning, they may have to run the engine 4-5 times a day, and many have auto start to do that when the batteries go low. The AC takes about 100 amps, so they need to run about 50% of the time in most cases. I do think this is made worse because the alternators are thermal cycling and not putting out anywhere near the rated amps over time.

Personally, I don't think that trying to run air conditioning is a viable thing to do, and don't support even trying to design a system to do it. Having an RV that used 200ah per day can be done successfully if you drive a lot with a smaller alternator, but if you are in a location for an extended time it is tougher. By going about to the limits of the 4/0 cable that is commonly used of about 250 amps allows enough recovery from the occasional trip to a trailhead, store, or dump station can keep up fairly well.

All of this said, I don't like the current setups that are being used for a few reasons. I think they are running the systems too hard as they seem to be perpetually in thermal cycling, which is not a good thing. I also don't like the way do the charging control, which is almost always with a Balmar regulator. Our solar and shore chargers both do charge control based on the shunt measured amps to the batteries, so they get the batteries to totally full without overcharging. All of regulators I have seen use an algorithm (so do most shore chargers) to control the charging and will nearly always over or undercharge the batteries, but most commonly undercharge. I think the Ample Power unit will run off the amps is you have the System Controller(?). We don't need the engine charging to be automatically controlled, as whenever we are charging, we are driving anyway and can watch the ammeter, so the V3 with it's ability to be held in absorption or pushed to float can easily be done manually for us.

The dual alternator setup came from the desire to have a bit of redundancy. It seemed better to run two 250 amp units at low, less damaging, loads than to run one 250 amp unit hard, and carry a spare. Added to that the fact that we won't have thermal control on them makes it even more desirable to run them easier. We would use the two output reductions, I think, with one set fairly high for the short trips near a campsite, and a lower one (which would be close to what the Primer recommended) for the long driving days.

Does the V3 change charge stage immediately when you throw the switch, or does it do a gradual transition? Same question with the output limiting?

Hopefully, we will be able to make this work out well for us. Is there anything that we are assuming or want to accomplish that the V3 wouldn't be able to do?

[Coulomb]

It's a little strange to buy a high output alternator and then throttle it with temperature sensing that is not under their control.

As you have noted Balmar can turn a 270 Amp alternator into a 160 Amp unit.

An alternate solution would be to install a thermostat on the alternator that switches at a desirable setpoint and feed the output into a current limit input on the V3.

The V3 has a fairly short ramp time. Current limit is very quick to take effect.

[Lever]

It's a little strange to buy a high output alternator and then throttle it with temperature sensing that is not under their control.

As you have noted Balmar can turn a 270 Amp alternator into a 160 Amp unit.

An alternate solution would be to install a thermostat on the alternator that switches at a desirable setpoint and feed the output into a current limit input on the V3.

The V3 has a fairly short ramp time. Current limit is very quick to take effect.

I assume you are referring to some kind of temperature control switch to control the current limiting inputs? I actually have been looking for such products, but have not been successful to this point. Do you have a source or brand to get me in the right direction?

[Coulomb]

Close to 4000 to choose from here:

https://www.digikey.com/product-search/en/sensors-transducers/temperature-sensors-thermostats-mechanical/1966363?k=thermostat

[Lever]

Thanks, I was using the wrong search terms, didn't even think about thermostat.

I don't know if I would use them to control the limits or not at this point, but would certainly be nice to have a couple of temps to illuminate lamps. Maybe on set at maximum safe temp that we would like to run, and another a bit below the highest the alternator could take. They could be very valuable for setting the levels for the limits, I would think.