Charging AGM batteries with 50amp load

[ThanksForAllTheFish]

Hey all,

Details on (part) of planned setup:

Whenever I state a componets wattage, I am overstating it to account for inverter efficiency loss... So inverter is accounted for

Componets:
*aftermarket alternator to replace OEM alternator on 2001 ECONOLINE E150 4.6L - This aftermarket alternator will provide 100amp at idle with a max of 250amp (not sure what rpm to hit that, contacted mfg)
*200ah agm deep cycle battery
*3000W continous 6000W peak pure sin wave inverter (60hz)
*battery monitor with shunt resistor so I don't kill my battery
*130w mini fridge with estimated 33% duty cycle, so continous load of ~ 43w or ~12v @ 3.6a
*Window AC unit - 5000btu 600w with estimated startup wattage of 3000w. Assuming 100% duty cycle while vehicle is running... So 12v @ 50a
*battery charging - unknown

Planned usage:
Attach inverter to agm battery. Attach fridge to inverter and run fridge 24/7. Attach AC to inverter and run ONLY WHEN VEHICLE IS RUNNING.

Question:

I'm trying to figure out a good way to charge the AGM battery at a rate of atleast 40A on top of the 50A load from the AC. I have thought about just tieing the AGM battery directly to the alternator and sucking up my capacity loss... I have also thought about using an isolater, but that won't quite get me full either. I relaize I could get a massive 100a dc to dc charger but I really don't want to spend that much. I would rather take a battery capacity loss and/or shroter lifespan.

I have considered getting another inverter and running the AC off an inverter tied directly to alternator, but I am concerned it will be harmful to alternator/not work because of the AC startup wattage. I was also considering doing what I mentioned above but have another car battery between alternator and inverter.

Anyway, does anyone have any good ideas that I missed? Otherwise, does anyone here charge AGM batteries off of alternator?

Thanks,
-Sam

[avanti]

Hi and welcome.
Are you talking about a second engine alternator, or simply a larger replacement for the chassis alternator? If the latter, what kind of van/engine are we talking about?

[ThanksForAllTheFish]

Avanti,

I plan to replace oem chasis alternator with aftermarket alternator on a 2001 econoline e150 4.6L.

Thanks,
-Sam

[booster]

Originally Posted by ThanksForAllTheFish

Avanti,

I plan to replace oem chasis alternator with aftermarket alternator on a 2001 econoline e150 4.6L.

Thanks,
-Sam

A 250 amp internally regulated alternator will probable run at 180+ amps hot, which will be too hot for it to handle long term, so limiting is a good idea for it also.



We have found that the Lifeline AGMs we use can take about 40%C in amps, so 200ah would be about 80 amps before it would start to get too hot on a long charge. 40 amps is reasonable to recover them fine.


I would leave the big inverter off and get a small, low parasitic one for the frig off the switched coach power from the battery. That frig is going to use near half of your usable capacity every day.


What AC are you running that uses 50 amps? How much when compressor cycles?


It sounds like the problem would be if you limited the power to the coach, when the AC cycles the batteries might get more than they need or less than you like depending on where you limit.



You probably want to limit your alternator output to stay under about 100-110 amps as you mention. B to B would work, maybe a combination of the Victron split charge relays could be done.

[ThanksForAllTheFish]

Originally Posted by booster

1.
A 250 amp internally regulated alternator will probable run at 180+ amps hot, which will be too hot for it to handle long term, so limiting is a good idea for it also.


2.
We have found that the Lifeline AGMs we use can take about 40%C in amps, so 200ah would be about 80 amps before it would start to get too hot on a long charge. 40 amps is reasonable to recover them fine.

3.
I would leave the big inverter off and get a small, low parasitic one for the frig off the switched coach power from the battery. That frig is going to use near half of your usable capacity every day.

4.
What AC are you running that uses 50 amps? How much when compressor cycles?

5.
It sounds like the problem would be if you limited the power to the coach, when the AC cycles the batteries might get more than they need or less than you like depending on where you limit.


6.
You probably want to limit your alternator output to stay under about 100-110 amps as you mention. B to B would work, maybe a combination of the Victron split charge relays could be done.

I labeled your paragraphs above and responded to them one by one below:

1.

I am not all that familiar with charging batteries off alternator, are you saying I should get a componet to actively limit the current?

2.

So lets say I have a dead 150ah battery with a 150a alternator. For simpleness, lets say it truly outputs 150a and the car uses nothing. Will the battery charge at 150a (1C) thus overheating the battery? I guess what im getting at is if I keep giving this battery more power, it will just try and charge faster and faster correct?

3.

So from my understanding coach power is refering to the 200ah battery. You are saying I should power the fridge off the alternator (NOT THROUGH THE 200ah BATTERY) whenever the vehicle is running? Im abit confused on this.

EDIT:
I think what your saying is get a smaller inverter to use for the fridge running off of the coach (200ah) battery. Not sure what you mean by switched? Isnt the coach power always ON, and charging when car is on?

4.

600w window ac unit. In DC at 12v that is 50amps. 12*50=600

From googling around, it seems like the rule of thumb for compressor current on startup is 5-7x the wattage rating. So if its 5x, that puts us at 3000w. If I get an inverter that is 3000w continous and 6000w peak I hope I am OK.

5.

Yes that is my problem, I need a way to charge the COACH battery while also supplying 50amps through the 200ah battery for the window AC.... What if I run an isolator and dc dc charger in parallel?

6.

If I run battery to battery, with no isolators or anything, how much capacity do you think I would loose? (Im fine running batteries to 30%, I just need the battery to last for a couple months of use)

Thanks a bunch,
-Sam

[markopolo]

Sam - what you first posted on the forum would work with the addition of something like this -> https://www.bluesea.com/products/cat...harging_Relays <- between the starting battery and the auxiliary batteries.

Booster mentioned possibly supplying to much to the auxiliary batteries but if it's short term as you later mentioned then maybe that's not a big problem.

I can confirm the approximate 50A draw of a 5000 BTU unit. The startup surge often causes a problem for the 1500W inverter I have in my van so your choice of a larger inverter should work.

[booster]

Answers in red

Originally Posted by ThanksForAllTheFish

I labeled your paragraphs above and responded to them one by one below:

1. Your battery probably will accept at least 120-140 amps and the alternator will do over that so, as Marko said, unless short periods, we see heat issues in about 20 minutes on the batteries at those kinds of rates, you probably would need to limit the current. The other question is how big your wiring is as we are talking quite large currents.

I am not all that familiar with charging batteries off alternator, are you saying I should get a componet to actively limit the current?

2. It may not get to 150 amps for more than a short flash, but as said above it will accept enough to overheat itself. We have found that point to be at about .4C amps, so 40 amps per 100ah of capacity.

So lets say I have a dead 150ah battery with a 150a alternator. For simpleness, lets say it truly outputs 150a and the car uses nothing. Will the battery charge at 150a (1C) thus overheating the battery? I guess what im getting at is if I keep giving this battery more power, it will just try and charge faster and faster correct?

3. If the battery on charge and getting current, nothing is running on the battery, as everything is just taking power from the charge source going to the battery. Nothing just goes through a battery as such, just in and out depending on if on charge or not. The frig would connect to the battery, probably through your 12v battery on switch like the rest of the van. So yes, the alternator will be running the frig and everything else. The small inverter is just so you could shut off the main big, less efficient inverter to save energy when on batteries.

So from my understanding coach power is refering to the 200ah battery. You are saying I should power the fridge off the alternator (NOT THROUGH THE 200ah BATTERY) whenever the vehicle is running? Im abit confused on this.

EDIT:
I think what your saying is get a smaller inverter to use for the fridge running off of the coach (200ah) battery. Not sure what you mean by switched? Isnt the coach power always ON, and charging when car is on?

4.

600w window ac unit. In DC at 12v that is 50amps. 12*50=600

From googling around, it seems like the rule of thumb for compressor current on startup is 5-7x the wattage rating. So if its 5x, that puts us at 3000w. If I get an inverter that is 3000w continous and 6000w peak I hope I am OK.

5. Those items would have to be in series or it would just run on one or the other, but both wouldn't normally be needed. A 100 amp B to B would do most all of what you want, but you mentioned too costly.

Yes that is my problem, I need a way to charge the COACH battery while also supplying 50amps through the 200ah battery for the window AC.... What if I run an isolator and dc dc charger in parallel?

6. You are only going to lose capacity if the batteries don't get charged full, and they can get full on a very wide range of charge rates as long as the voltage is correct to finish the charge. The only difference with more or less amps would be how long it takes to get full. If you run out of time to get full, the actual amount you are short would depend on how low they were at the start of charging and how long you charged at whatever average amps.

If I run battery to battery, with no isolators or anything, how much capacity do you think I would loose? (Im fine running batteries to 30%, I just need the battery to last for a couple months of use)

Thanks a bunch,
-Sam

[jakegw2]

You don't need a separate alternator to charge your AGM. AGM and lead-acid batteries are pretty tolerant of abuse as long as you do not drain them to empty. The lead-acid start battery and AGM batteries will coexist just fine, though perhaps with a very slightly shortened lifespan. I do recommend automatically separating them when they are not charging, but that is it.

Your inverter is probably oversized for the application. Inverters have a continuous rating and a peak rating. You need the peak rating to start the compressor and the continuous rating to run it. For your application an inverter that can do 2000W continuous and 3000W peak (a common spec) could almost certainly handle your AC.

You will be dealing with the peukert effect in your configuration. The draw on the battery will be around 25% of its capacity (0.25C in battery parlance). AGM gets unhappy over 20% (0.2C) and the resulting actual usable capacity drops. This is probably not to terrible at 0.25C, but if you could squeeze in 300Ah you could avoid the problem entirely.

Battery isolation doesn't need to be complicated. The simple way to do it is to add a solenoid that can handle 150A or so and connect the activator to the chassis ignition power. When the van is running the house and chassis batteries are connected. When it is off they are disconnected. The charging voltage delta between AGM and lead-acid is trivial, and since they are disconnected when not charging the resting voltage difference is irrelevant.

Summary - add a disconnect solenoid and an extra 100A to your system and you should be good to go. The extra 100A is optional. If you are only need them to last a few months then the solenoid is optional too.

[booster]

Not cheap but I think one of these would limit the current to the coach so you would good to your batteries and alternator and it should give adequate power to run coach AC, frig, and charge at a reasonable rate.


https://www.mastervolt.com/products/...e-mate-pro-90/


You likely will have the dash air on too, so the van is going to be using at least 40 amps, I think, so 130 continuous out of the alternator is probably a good place to be in hot weather.