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Discussion Starter #1
Hi all,

I've been reading posts via the search function and I still can't understand why its frowned upon to charge your house batteries via the Alternator.

Most newer PM's come with the 220A alternator and AGM battery from factory. If its designed to use and charge AGM batteries, then why would we need anything more than a fuse and cut off in-between the starting and house batteries?

220A seems like overkill for 1 95AH battery? I'm new to all this so forgive me if this seems like a stupid question.
 

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No stupid questions here. First, it is NOT frowned upon to charge house batteries with the alternator (via the starter battery). Most all commercial RVs do it, and nearly all of us here do, too !! Many of us have more than one charging source. Both alternator and solar is really common. Shore power and generators are also options.

Second, the standard for every gas engine PM ever made is a 180A alternator and a maintenance-free flooded (FLA) battery. Only diesels came with AGMs. The 220A alternator is an option, one that no one has proven to be advantageous in an RV conversion. I have one and I see the exact same 80A max going to the house bank as those that have the stock 180A alternator. It was a "why not" upgrade that I would not do again.

Why more than just a cut-off and fuse? Well, most "battery isolators" are just a cut-off of one type or another. Most are relays, Battery Doctor and Stinger, being common ones. And there are more expensive ones with some "smarts" that help manage the cut-off for you. There is also a new wave of units known as "battery-to-battery" (B2B) chargers. There are LOTS of options that all do the job. Do some research, check your pocketbook, and pick one.
 

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Discussion Starter #3
No stupid questions here. First, it is NOT frowned upon to charge house batteries with the alternator (via the starter battery). Most all commercial RVs do it, and nearly all of us here do, too !! Many of us have more than one charging source. Both alternator and solar is really common. Shore power and generators are also options.

Second, the standard for every gas engine PM ever made is a 180A alternator and a maintenance-free flooded (FLA) battery. Only diesels came with AGMs. The 220A alternator is an option, one that no one has proven to be advantageous in an RV conversion. I have one and I see the exact same 80A max going to the house bank as those that have the stock 180A alternator. It was a "why not" upgrade that I would not do again.

Why more than just a cut-off and fuse? Well, most "battery isolators" are just a cut-off of one type or another. Most are relays, Battery Doctor and Stinger, being common ones. And there are more expensive ones with some "smarts" that help manage the cut-off for you. There is also a new wave of units known as "battery-to-battery" (B2B) chargers. There are LOTS of options that all do the job. Do some research, check your pocketbook, and pick one.
Oh ok, I was under the impression that the batteries in the newer PM's were all AGM's and the alternators use AGM charging profiles.

It took some digging, but I found the window sticker for mine and it does confirm that I do have the 180A alternator. :(

For me it's just another charging source since I already have solar and a shore power hook up.
As much as I wanted to, I couldn't justify spending another $150-$300 on a DC 2 DC charger. I guess I will stick with the manual switch for now.

Thanks for the insight!
 

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My understanding (and others can and will correct me if I'm wrong) is that alternator charging is single-stage. It provides current to the battery at a single voltage (Bulk charge), regardless of the state of (dis)charge. Solar and AC battery chargers are all designed to provide multiple voltage levels depending on the level of the battery.

Before I understood this, I just had the alternator connected all the time and I'm convinced it dramatically shortened the life of my battery. I have a 240Ah Renogy AGM which I bought in 2017. After a year's use, never letting it discharge below 50%, the max voltage it holds is about 12.7 V, compared to 13.0 new.

It's possible it was just a defective battery or something else caused the damage but I'm not taking any chances anymore.

@SteveSS: I think maintenance-free lead acid is the same as AGM. I've never heard of a maintenance-free FLA. There are AGMs which are sealed lead acid (also referred to as "maintenance-free) and flooded lead acid which you need to add water. I'm pretty sure AGMs are standard on all PMs.
 

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No AGM’s on diesels only. There are sealed flooded, I recently discovered. You can’t add water to them but they are vented- who woulda thought?
 

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No AGM’s on diesels only. There are sealed flooded, I recently discovered. You can’t add water to them but they are vented- who woulda thought?
Thanks for the correction. According to this site, they're called Valve Regulated Lead Acid Batteries (VRLA) and are a simpler version of AGMs (or a more advanced FLA, depending on how you look at it). I had no idea they existed.

When I swapped out my vehicle battery, I put in an AGM and now I'm wondering if that was a mistake since the charging voltages are slightly different and, presumably, the alternator is calibrated to these VRLAs.
 

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Hi,
The advantage of having an isolator is that it will prevent the starting battery on the van from being run down by loads in the RV -- it does this by only connecting the house battery to the van battery/alternator when the engine is running. If you have a manual disconnect and you are 100% certain that you can remember to turn it off overnight, then you don't need the isolator, but if you forget, you could end up with a dead starter battery in the morning.
An example - there are dozens of them out there: https://www.amazon.com/Stinger-SGP32-Battery-Relay-Isolator/dp/B001HBYXVS/ref=sr_1_13?dchild=1&keywords=rv+battery+isolator&qid=1597277073&sr=8-13

For your battery, the 220 amp alternator is no advantagel over the 180 -- you will never see charging rates to that fairly small battery that the 180 could not supply.
I have 220 amp-hr flooded lead acid batteries and I've never seen more that 38 amps charging current -- it may be a bit more than that right after you start the van and have a discharged house battery, but this will only last for a few seconds.

People buy the B2B chargers because they want the house battery to be charged via the best 3 stage charging process. The idea is that this will make the house battery last longer. I think this makes some sense if you are protecting your investment in a couple thousand dollars of Lithium batteries, but probably not to protect a couple hundred dollars worth of lead acid batteries -- there are literally millions of RVs running around without a B2B charger.

Gary
 

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Discussion Starter #8
Hi,
The advantage of having an isolator is that it will prevent the starting battery on the van from being run down by loads in the RV -- it does this by only connecting the house battery to the van battery/alternator when the engine is running. If you have a manual disconnect and you are 100% certain that you can remember to turn it off overnight, then you don't need the isolator, but if you forget, you could end up with a dead starter battery in the morning.
An example - there are dozens of them out there: https://www.amazon.com/Stinger-SGP32-Battery-Relay-Isolator/dp/B001HBYXVS/ref=sr_1_13?dchild=1&keywords=rv+battery+isolator&qid=1597277073&sr=8-13

For your battery, the 220 amp alternator is no advantagel over the 180 -- you will never see charging rates to that fairly small battery that the 180 could not supply.
I have 220 amp-hr flooded lead acid batteries and I've never seen more that 38 amps charging current -- it may be a bit more than that right after you start the van and have a discharged house battery, but this will only last for a few seconds.

People buy the B2B chargers because they want the house battery to be charged via the best 3 stage charging process. The idea is that this will make the house battery last longer. I think this makes some sense if you are protecting your investment in a couple thousand dollars of Lithium batteries, but probably not to protect a couple hundred dollars worth of lead acid batteries -- there are literally millions of RVs running around without a B2B charger.

Gary
My thoughts exactly, but Killing my starting battery isn't my concern, I just wanted to charge my 400AH AGM battery bank via the alternator when driving around or idling parked.

A B2B charger is super convenient and will be added down the line, but for right now, I will stick with the manual switch if needed in a pinch. Its always off and I haven't needed it since upping the solar array and battery bank.

All that being said, I did get the info I was looking for so thanks to all for stopping thru to set me straight!
 

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My thoughts exactly, but Killing my starting battery isn't my concern, I just wanted to charge my 400AH AGM battery bank via the alternator when driving around or idling parked.

A B2B charger is super convenient and will be added down the line, but for right now, I will stick with the manual switch if needed in a pinch. Its always off and I haven't needed it since upping the solar array and battery bank.

All that being said, I did get the info I was looking for so thanks to all for stopping thru to set me straight!
Oops -- I was thinking the 95 AH battery you mentioned was your house battery, but I guess you were talking about the starter battery.

Nothing wrong with eventually using a B2B, but I'm guessing you will find its not really necessary in your case.

Gary
 

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For your battery, the 220 amp alternator is no advantagel over the 180 -- you will never see charging rates to that fairly small battery that the 180 could not supply.
I have 220 amp-hr flooded lead acid batteries and I've never seen more that 38 amps charging current -- it may be a bit more than that right after you start the van and have a discharged house battery, but this will only last for a few seconds.
When designing my system, I assumed my 500Ah AGM bank could draw a ton of charging amps, which is why I got the 220A alternator and sized the charge cable for 150A. However, I've never seen it sustain more than an 80A charge rate (usually less). It sometimes spikes higher for a second or two but quickly drops below 80A. I have a feeling the van's own charge controller is the limiting factor. It makes me wonder what they offer a 220A alternator for. Some have suggested it may last longer, but we have no supporting data.

Like many of us, I only use alternator charging when solar is insufficient. When I do use the alternator, I try to limit it to bulk charging. I switch it off around 85% SOC and let solar finish it, because the solar controller is multi-stage. I also have the option of shore power multi-stage charging when both alternator and solar are insufficient. That happens when we don't drive enough, the sun is obscured (all winter here), and/or our battery use is exceptionally high. It's a juggling act I enjoy most of the time, but it would be impossible without a good battery monitor.
 

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My thoughts exactly, but Killing my starting battery isn't my concern, I just wanted to charge my 400AH AGM battery bank via the alternator when driving around or idling parked.

A B2B charger is super convenient and will be added down the line, but for right now, I will stick with the manual switch if needed in a pinch. Its always off and I haven't needed it since upping the solar array and battery bank.

All that being said, I did get the info I was looking for so thanks to all for stopping thru to set me straight!
I do 90% (or more) of my charging from my 180A PM alternator. I used the 70amp upfitter fuse to tie my 250ahr AGM house bank & a chassis ground.

I used a Victron smart switch & manual switch so I can turn it off manually. We do not have solar & so far this simple charging system has worked exceptionally well for us. With a SOC of approximately 80% to 85% I will see around 60 amps charge rate.

Here is a graph @ 88% SOC;
65611
 

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Another note I thought of this morning on this topic regarding the 220A alternator

We purchased our “white” van “off the lot” new & it came with a 180A. IIRC the upgrade option cost for the 220A if we factory ordered was a minimal cost $200 or $300 CAN. We could not wait the promised 6 months, but if we did I would definitely order the 220A for the cost.

The 220A in Canada is included in the “Ambulance Package” & there must be a reason. The computer software & the PM hardware is a bit of a mystery to me (at least I have never seen the specs or software to see how it is controls ”regulates” the alternator.

I believe my current measurement (shown above) is indicating only the charge being drawn by my house battery bank 250Ahr AGMs. It is not measuring the rest of the PM’s demands. With this Direct Charge (no B2B to limit), I believe this will provide the largest current the PM system will allow.

It seems my 180AMP works fine, but for a few bucks more I would upgrade to the 220Amp. If Budgets are tight there is nothing wrong with the 180amp either & 60amps is a pretty decent charge. Caveat, I have only tested my system with 250Ahr Rolls AGMs, & think the charge system would provide a different charge with different batteries & different SOCs.
 

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Sorry for novice’s questions. I am just in the process of refreshing my knowledges of Ohm's law or better say studying it from squire one.
  1. How much Ah does PM use at maximum? Car battery+car AC+elctrical+other.
  2. What stops alternator from routing all current to house battery? Let’s say I have 400Ah lithium battery and it can take 0.5c i.e. 200Ah. If all the current goes to house battery then nothing left for car battery and car battery will be drained to 0.
As I can understand from GaryBis and SteveSS posts the PM system does not give more then 80Ah to house battery. Do we take it as a rule/PM electrical system setup and calculate that 100Ah ALWAYS go to PM system? I.e. ‘electrical brains’ take 180Ah from alternator and then distribute them by giving priority to 1) charging car battery, 2) brake/head/tail lights, dash board 3) AC, 4) any auxiliary equipment 5) charging house battery.

Thank you for the answers.
 

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Sorry for novice’s questions. I am just in the process of refreshing my knowledges of Ohm's law or better say studying it from squire one.
  1. How much Ah does PM use at maximum? Car battery+car AC+elctrical+other.
  2. What stops alternator from routing all current to house battery? Let’s say I have 400Ah lithium battery and it can take 0.5c i.e. 200Ah. If all the current goes to house battery then nothing left for car battery and car battery will be drained to 0.
As I can understand from GaryBis and SteveSS posts the PM system does not give more then 80Ah to house battery. Do we take it as a rule/PM electrical system setup and calculate that 100Ah ALWAYS go to PM system? I.e. ‘electrical brains’ take 180Ah from alternator and then distribute them by giving priority to 1) charging car battery, 2) brake/head/tail lights, dash board 3) AC, 4) any auxiliary equipment 5) charging house battery.

Thank you for the answers.
#2 is a good theoretical question. I dont have the answer except to say you'd need some super heavy duty equipment to get 200 AH to the house battery. Any wire/solenoids/isolators we vanbuilders are likely to use is going to deliver much less than 200ah. I would note that I occasionally get over 80ah to my AGM house battery from my 220a alternator.

I did read that AGM do better with very high c rates (.2-.4) so its possible that its hard/expensive to find a B2B with high enough amperage for your AGM battery bank:
 

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Thank you afox.

I am afraid that house battery can draw too much leaving nothing for car battery. I am OK with max 80Ah going to house battery:). My question is what stops house battery from drawing all 180Ah from the alternator. This is not a question for 95Ah AGM house battery as it draws only 9.5Ah at 0.1c. Even with 0.4c it will draw just 38A. My plan is to have 280Ah LiFePo battery and theoretically it may take 140A with 0.5c.
 

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Search and read up about Battery Isolators

"Battery isolators can ensure that the starting battery has enough power to restart the engine while also recharging itself. Their main function is to divide direct current (DC) into several divisions, which allows current to move in a single direction. This provides the user the ability to charge multiple batteries from a single source of power.
A battery isolator kit provides everything that is needed to isolate two batteries, so they can be charged independently through the alternator while isolating the starting battery from the second battery. In addition, the battery isolator switch override/reset button allows the user to change the batteries to parallel mode for jump starting."
 

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Thank you afox.

I am afraid that house battery can draw too much leaving nothing for car battery. I am OK with max 80Ah going to house battery:). My question is what stops house battery from drawing all 180Ah from the alternator. This is not a question for 95Ah AGM house battery as it draws only 9.5Ah at 0.1c. Even with 0.4c it will draw just 38A. My plan is to have 280Ah LiFePo battery and theoretically it may take 140A with 0.5c.
This is why I used a DC-DC charger. Not a problem right now with 1 LiFePO4 battery (charges at 0.5C = 50A), but when I upgrade to 3, then the potential 150A draw is going to be hard on my alternator, even though I ordered my van with the optional 220A one.
 

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I think that fancy isolators may have the capability to intelligently divvy up charging current between house and start battery, but dumb ones (most of them I think) are just relays that either connect or disconnect the house battery from the charging. The start battery is always connected to the charging.

That said, in 30+ years of using dumb isolators I've never had a case of not keeping the start battery charged up and I don't remember anyone here ever reporting such a problem?

Gary
 
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