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Old 02-28-2021, 12:04 PM   #1
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Charging house batteries while driving

I have an Interstate GT EXT. The Airstream tech told me that the engine doesn't charge the house batteries very well while driving. I saw on one thread that the engine generator sends 100amps to the house batteries. Does anyone know if this is true?

I have 4 120 amp hour lithium ion batteries for a total of 480 amp hours. If my house batteries are completely discharged, how long would it take for the engine generator to completely charge them if I am going 60mph?

Thanks in advance for your reply
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Old 02-28-2021, 01:02 PM   #2
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I have 3-160 amp hour lithium batteries. They were professionally installed in 2017. I have a 2013 Lounge Ext (should say ďmodifiedĒ with all the interior renovations done).
I am using the engine alternator in a manual mode. I have a disconnect switch between alternator and house batteries. I see up to 60amps going to the house batteries at the most. Iím not sure if it because I use it to top off the batteries, or the BMS is limiting the current. I have the stock alternator.
I canít find it, but there is a thread out here that goes more in depth into this and the impact it can have on the alternator.
If in doubt, snap on an ammeter and see what is flowing with engine charging. Granted, thatís a driveway test, not on the road.
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Old 02-28-2021, 04:39 PM   #3
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Charging house batteries while driving

We had a similar problem: 400Ah of Lithium batteries, a perfectly good alternator under the hood, and almost no current going to the coach batteries while the engine was running. Our upgrade contractors figured it out, and we now have the kind of current one should expect from the alternator to the coach batteries. What it boils down to, I'm afraid, is that Airstream apparently doesn't have the foggiest idea how to correctly do something even this basic. Our guys said they replaced the OEM battery isolator / combiner with a Victron Cyrix device, replaced a 150 amp DC fuse with a bigger one, ran some new wiring, and voila! I wish I could tell you exactly how they did it, but I paid them to do it instead of doing it myself, so I don't really know the details. Bottom line, Airstream is right about their lousy wiring job not enabling this, but it can be done correctly with excellent results.
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Old 02-28-2021, 04:58 PM   #4
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Quote:
Originally Posted by Muckinabout View Post
I have an Interstate GT EXT. The Airstream tech told me that the engine doesn't charge the house batteries very well while driving. I saw on one thread that the engine generator sends 100amps to the house batteries. Does anyone know if this is true?

I have 4 120 amp hour lithium ion batteries for a total of 480 amp hours. If my house batteries are completely discharged, how long would it take for the engine generator to completely charge them if I am going 60mph?

Thanks in advance for your reply
The generator may (if able to) charge at 100 amps but most are limited to about 70. Re how long that may take - assume most of the day as the charge rate drops off as battery voltage rises.

Collyn
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Old 02-28-2021, 06:11 PM   #5
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Originally Posted by Rocinante View Post
We had a similar problem: . . . What it boils down to, I'm afraid, is that Airstream apparently doesn't have the foggiest idea how to correctly do something even this basic. Our guys said they replaced the OEM battery isolator / combiner with a Victron Cyrix device, replaced a 150 amp DC fuse with a bigger one, ran some new wiring, and voila! I wish I could tell you exactly how they did it, but I paid them to do it instead of doing it myself, so I don't really know the details. Bottom line, Airstream is right about their lousy wiring job not enabling this, but it can be done correctly with excellent results.
Yes - the Airstream OEM battery isolator is useless if you have any solar. In daylight solar raises the house battery voltage and the isolator thinks they are charged because it only monitors voltage. I added a manual switch to mine so I can force a battery connection if needed. Works great and only involved changing the battery boost switch by the drivers LH knee to allow constant connection rather than the momentary switch installed by Airstream. Also added a current meter so I can monitor the energy flow to and from the batteries.
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Old 02-28-2021, 06:40 PM   #6
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Alternator voltages aren’t idea for lithium. I would recommend adding a sterling battery to battery charger or similar device.
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Old 02-28-2021, 08:56 PM   #7
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Alternator voltages arenít idea for lithium. I would recommend adding a sterling battery to battery charger or similar device.


My unit has Orion DC/DC Converter between alternator and coach batteries.
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Old 03-01-2021, 07:57 AM   #8
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Originally Posted by toskeysam View Post
My unit has Orion DC/DC Converter between alternator and coach batteries.
Orion is also a good choice. Our guys went with Cyrix because it can move more amperage between the systems.
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Old 03-01-2021, 09:14 AM   #9
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Everyone responding seem to have Lithium Ion batteries. Does this same issue apply to AGM batteries?
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Old 03-01-2021, 09:18 AM   #10
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Probably, though lead-acid batteries will take longer to charge due to their more asymptotic charging curve and their resultant need for an extended absorption phase to get them to 100%. We are much happier with lithium batteries for the coach and would never go back.
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Old 03-01-2021, 09:39 AM   #11
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The problem arises from the the fact that the vehicle and the house batteryís are not the same type. Flooded, agm and lithium ion batteryís all have different charge
Rates and float voltages. If they are truly using
An isolator then there is seven tenths of a volt loss
Thru the diode. I think you will end up finding out that you can get a partial charge with the engine alternator but the only to get 100 percent charge is to plug in and use the charger converter.
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Old 03-01-2021, 02:41 PM   #12
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What he said...

Quote:
Originally Posted by LB_3 View Post
Alternator voltages arenít idea for lithium. I would recommend adding a sterling battery to battery charger or similar device.
The problem you are describing is common to boats, motor homes and trailers (thatís me)... where the motor-driven charging system is for lead acid batteries but the house batteries are lithium.

I happen to use a Victron Orion Smart TR to charge my Battle Born lithiums in the trailer from the truck. Works great and is fast. Sterling makes similar products. They are generically known as ďDC to DC chargersĒ or ďDC to DC convertersĒ. They manage the voltage differences between the lower voltage lead acid and higher lithium. They can also draw the right amount of current from the motor/alternator side to avoid damage to the alternator from being asked to feed a much larger load (maintaining the house batteries) than just its own starting battery.

Upgraded wiring is probably needed, too.

You may want to look at (or find a competent RV shop to look at and install) a Victron Orion Smart TR 12/12/18. Thatís 12 volts in (but it runs on as little as 8), 12 volts out (but programmable up to 16 volts... my lithiumís want to be charged at 14.6) and 18 amps. They also make a 12/12/30 which is what I use. My alternator is 150 amps. You may not want to draw 30 amps continuously from a 100 amp alternator. Some knowledgeable Mercedes person can answer that better.

Anyway, there is a solution out there for what you are experiencing.
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Old 03-02-2021, 12:07 AM   #13
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Sorry, this got long....

The wiring does not need to be upgraded per say from the alternator. The problem arises from the function of the alternator and how much current can be drawn from it without burning in it out.

The issue is not in different battery technologies between the house battery and the chassis battery either. Don’t think that you need to go change out your chassis battery just to fix the problem.

It is not as much of an issue with conventional batteries and AGM batteries. I don’t want to say there is no issue at all, as that is technically not correct. But you won’t run into the issues with AGM batteries and conventional batteries because they fill or top off more easily, or as they talk in the video, has a higher internal resistance over Lithium. Lithium can take such a charge over and beyond an AGM battery or a conventional battery, it draws from an alternator above and beyond the other two types of batteries. The problem has to deal with overheating the alternator.

Victron has a video that explains the reason quite well. Around 5:37, they explain the difference between battery draws on the alternator. I suggest watching the entire video though, boring as it might be, to understand the situation as a whole.

https://video.search.yahoo.com/searc...d&action=click

I’m not fantastic at correctly talking about technical aspects, but the Precision Circuits LI-BIM turns on and off the current I believe at 15 minute increments. Therefore it allows the alternator to cool in between draw, effectively not allowing it to burn out.

I don’t understand or remember the details of DC-DC converters in depth just because I went with the Li-BiM. If I remember correctly, a DC-DC converter controls energy and regulates how and when the lesser of the two electric draws receive current.

I was told by Precision Circuits that their Li-BiM does have some way of deciding when the lithium battery needs current or not. Kind of obvious, but I wanted to confirm that as that seems to be one of the questions holding back some from using the Li-BiM.

Whether each of us has a DC-DC converter, the Li-BiM, or other options out there, there has to be some way for your lithium battery not to burn out the alternator. If you think about it, a lithium battery stores more energy and charges faster than any other technology out there. It’s the exact reason why the draw off the alternator needs to be regulated. Lithium batteries draw power in faster and at a larger capacity, in which if it is not regulated, will burn out an alternator. Like I said, the Victron video explains it much better.

Since the voltage coming off the alternator has to be regulated in some manner with lithium batteries, it will never be the most efficient manner for your batteries to recharge. They benefit from sources where they can pull a higher current at a faster rate. Just because it’s a slower charge rate though doesn’t mean that alternator charging is not part of the equation.

Here’s a little warning. There are some tricks to pull power off your alternator and let the voltage flow to your batteries, but you risk damage to your alternator. It might not happen immediately, but over time, which is an unknown, might be a week, year, don’t know, your alternator can overheat or that heat causes failure over time. It can damage your alternator and your only option will be to replace it. There will probably be people who tell you they fixed the problem for you as a consumer, and you would be unknowing to this problem unless you educate yourself into why this is bad.

Just to add a side-note, there’s talk about adding a alternator or changing it out for a bigger alternator, I also do not want to dive into the debate whether a good thing or not.

It’s best to realize that this is a limitation and constraint that lithium has and find your solution to regulate the power that is drawn off your alternator. It just is what it is.

Lithium allows for more storable power, but it also allows for a quicker method of charging above AGM and conventional lead-acid batteries. It also allows you to have more usable power above the other two, also. They are correct in telling you the alternator is not the best source of charging for Lithium, but best to understand why this is. I highly suggest watching the video to help understand why.
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Old 03-02-2021, 06:39 AM   #14
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Sorry, this got long....

The wiring does not need to be upgraded per say from the alternator. The problem arises from the function of the alternator and how much current can be drawn from it without burning in it out.

The issue is not in different battery technologies between the house battery and the chassis battery either. Donít think that you need to go change out your chassis battery just to fix the problem.

It is not as much of an issue with conventional batteries and AGM batteries. I donít want to say there is no issue at all, as that is technically not correct. But you wonít run into the issues with AGM batteries and conventional batteries because they fill or top off more easily, or as they talk in the video, has a higher internal resistance over Lithium. Lithium can take such a charge over and beyond an AGM battery or a conventional battery, it draws from an alternator above and beyond the other two types of batteries. The problem has to deal with overheating the alternator.

Victron has a video that explains the reason quite well. Around 5:37, they explain the difference between battery draws on the alternator. I suggest watching the entire video though, boring as it might be, to understand the situation as a whole.

https://video.search.yahoo.com/searc...d&action=click

Iím not fantastic at correctly talking about technical aspects, but the Precision Circuits LI-BIM turns on and off the current I believe at 15 minute increments. Therefore it allows the alternator to cool in between draw, effectively not allowing it to burn out.

I donít understand or remember the details of DC-DC converters in depth just because I went with the Li-BiM. If I remember correctly, a DC-DC converter controls energy and regulates how and when the lesser of the two electric draws receive current.

I was told by Precision Circuits that their Li-BiM does have some way of deciding when the lithium battery needs current or not. Kind of obvious, but I wanted to confirm that as that seems to be one of the questions holding back some from using the Li-BiM.

Whether each of us has a DC-DC converter, the Li-BiM, or other options out there, there has to be some way for your lithium battery not to burn out the alternator. If you think about it, a lithium battery stores more energy and charges faster than any other technology out there. Itís the exact reason why the draw off the alternator needs to be regulated. Lithium batteries draw power in faster and at a larger capacity, in which if it is not regulated, will burn out an alternator. Like I said, the Victron video explains it much better.

Since the voltage coming off the alternator has to be regulated in some manner with lithium batteries, it will never be the most efficient manner for your batteries to recharge. They benefit from sources where they can pull a higher current at a faster rate. Just because itís a slower charge rate though doesnít mean that alternator charging is not part of the equation.

Hereís a little warning. There are some tricks to pull power off your alternator and let the voltage flow to your batteries, but you risk damage to your alternator. It might not happen immediately, but over time, which is an unknown, might be a week, year, donít know, your alternator can overheat or that heat causes failure over time. It can damage your alternator and your only option will be to replace it. There will probably be people who tell you they fixed the problem for you as a consumer, and you would be unknowing to this problem unless you educate yourself into why this is bad.

Just to add a side-note, thereís talk about adding a alternator or changing it out for a bigger alternator, I also do not want to dive into the debate whether a good thing or not.

Itís best to realize that this is a limitation and constraint that lithium has and find your solution to regulate the power that is drawn off your alternator. It just is what it is.

Lithium allows for more storable power, but it also allows for a quicker method of charging above AGM and conventional lead-acid batteries. It also allows you to have more usable power above the other two, also. They are correct in telling you the alternator is not the best source of charging for Lithium, but best to understand why this is. I highly suggest watching the video to help understand why.


Frankly, not too long of a posting. You succinctly related all the information contained in very long and multiple postings in other threads. What you presented here is precisely why we treat our alternator-charging mode as a manual switch on/off capability and use only when needed. We didnít want to rely on an automatic setup...and didnít want to experience ďvan-death-by-alternatorĒ on the road. Thank you!
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Old 03-10-2021, 09:18 AM   #15
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Boy, I have an Interstate 24 GT coming in 2 months and I wish I understand any of these replies. It has solar and lithium batteries. Apparently, my brain is not wired to understand electricity at all. Simply over my head. I read these to try and get educated but it doesn’t seem to work. Would someone wanna bottom line these conversations for a complete idiot to understand?

Thank you.
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Old 03-10-2021, 10:16 AM   #16
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Charging while driving

We have a significantly modified 2013 AI and use the Li-BiM to get about 60 amps off and on while driving.
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Old 03-10-2021, 05:16 PM   #17
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[QUOTE=LB_3;2466576]Alternator voltages arenít idea for lithium. I would recommend adding a sterling battery to battery charger or similar device.[/QUOTE

I went with the Sterling. I like that it draws off the chassis batteries and ďliftísĒ the charge if needed. It just seems the smart way to preserve the alternator. SCHMITTE went with a Charge Master Pro which is another superior product. He also tied it to the battery bms if I recall correctly.
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Old 03-10-2021, 09:30 PM   #18
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When driving we are getting about 12-14 amps at 14.4 V into a LiFePO4 battery bank. Stock F 250 alternator.

We use a DC/DC converter.

If the sun is out add several amps to that.

This is an important charging/energy source for us.
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Old 03-10-2021, 09:37 PM   #19
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Quote:
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Boy, I have an Interstate 24 GT coming in 2 months and I wish I understand any of these replies. It has solar and lithium batteries. Apparently, my brain is not wired to understand electricity at all. Simply over my head. I read these to try and get educated but it doesnít seem to work. Would someone wanna bottom line these conversations for a complete idiot to understand?

Thank you.
It is not over your head.
It is just new information for your head.

Spend some time and look up voltage and current on the internet.
And stop bashing your brain.
Your brain has no problem. Just help it out.

Look up current.
Look up voltage.
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Old 03-10-2021, 10:21 PM   #20
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That victron video was carefully staged to prove a point which might apply in very limited circumstances and unfortunately has been morphed into a genuine urban myth and then into hard fact.

The truth is, for a TT or Fiver where power is supplied from the alternator via the standard trailer plug and socket and a 15 amp fuse and 40 feet of skinny wiring to a battery, there is absolutely no chance of burning out a standard alternator at any engine revs. In practice, you will be lucky to get 15 amps flowing and probably less if your lithium batteries are more than half full.

However, do this in a motorhome with short runs and larger batteries that are close to depleted and then you ARE in a situation where the victron scare MIGHT be relevant.

The other myth is that a B2B charger will solve the problem. Keep it modest - 20 to 40 amps maximum and you might be right, but if you are the bigger is naturally better type and go for a 70 amp sterling unit, it can be that it will faithfully deliver 70 amps until the generator gives up trying to supply that plus the lights plus the aircon and burns out.

And there are alternators and alternators and some are very capable of protecting themselves and the vehicle system from attempts at getting more power than they want to give.

Recently read a post on a specialist RV Solar group where someone did a comparison between standard split charging and charging via a B2B unit and he found that provided the split charger was contactor driven rather than by diode, the split charger did better over a 4 hour driver than the B2B. of course it was valid under his test conditions and not necessarily a universal truth.

I recall similar assertions years and years ago by an Australian expert in his field, so obviously the laws dictating things electrical haven't changed even with new battery types
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