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Old 02-14-2020, 07:31 AM   #41
Graphite Dave
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Default Re: General questions about alternator charging

Quote:
Originally Posted by Redridge View Post
you guys need a BIRD, this is standard practice in the motorhome ind. https://pdxrvwholesale.com/products/...d-00-00362-100

here is the relay that can charge both batteries at once when the chassis battery is fully charged (by the alternator) https://pdxrvwholesale.com/products/...y-00-00507-512
The problem with a relay is the house battery is not charged with a charge profile that matches the battery construction. Not charged with a 3 stage charge. Bulk, Absorb, Float.

If two batteries are charged together they should be the same size, brand, type and even same manufacture date.

ACL will work but battery life is reduced.
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Last edited by Graphite Dave; 02-14-2020 at 07:43 AM.
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Old 02-14-2020, 09:01 AM   #42
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Default Re: General questions about alternator charging

[QUOTE=sparkplug;842348]I'm going to answer this post even though I'm a lot less knowledgable than many on here when it comes to electrics. My reason for doing so is that I have a working solution in my van so am happy to share my personal experience.

1. Newer NCV3 alternators are 'smart' alternators and will sense the amount of load and adjust their output accordingly. In the real world I think that your 220A alternator is never going to struggle to charge your house batteries. Unless your vehicle battery is failing you should be OK. Yes, some of the power will be needed by the van but the extra load demanded by the house batteries will simply make your alternator generate the extra current required.

2. Yes. When I installed mine I didn't have very much knowledge and didn't really do as much research as I perhaps should have done. I have a Duritic Voltage Sensitive Relay (VSR) which is not as good as a DC-DC (aka Battery to Battery or B2B system) - however it still works absolutely fine for me as I have an older 'dumb' alternator. VSRs will NOT work with 'smart' alternators. I am not aware of any downsides to this approach. Renology seem to have a good reputation in the US. In the UK I hear of a lot of people using the Sterling B2B units. There's an article which I found quite helpful here

IThanks Spark plug, I also have a Durite VSR, which I find slightly problematical, I have a solar system & charger (Trimetric) & while the engine is running I see current going into my leisure batteries but as soon as I stop I see current coming back out. I presume that is because the batteries are different sizes, I have 2 6 volt Crown 260 amp hour leisure batteries wired in series, I have been told by the support at Trimetric that I could use their solar charger as a battery to battery charger if I installed a 35amp fuse & a3 way switch between alternator Solar panels & charger but I don't know if current draw from leisure batteries would still take place. Sorry if this is slightly off topic, cheers, Roodster,
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Old 02-14-2020, 01:02 PM   #43
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Default Re: General questions about alternator charging

All alternators are load sensing, otherwise they would output 50V when you turn your headlights off. The NCV3 with 4 cylinder engine has a energy saving alternator profile which appears to be aware of battery current from a crude shunt. This allows it to throttle back voltage to a lower level once the starting battery is fully charged, thus saving a bit of fuel. This alternator has a lower voltage, and does not do a good job of charging lead acid batteries directly.

The V6 NCV3 alternator control is a single voltage design. (around 13.7-14.0V?). It does a better job charging lead acid batteries. Its not going to get the batteries to 100% full on its own (in any reasonable time). Typically none of the standard alternators are suitable as the sole charge source for a lead acid battery. But they are a valuable contributor, and as part of a solar/shore system, they can be effective and inexpensive means to get additional AHs into the battery pack.
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Old 02-14-2020, 03:47 PM   #44
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Default Re: General questions about alternator charging

I think most of VR observe voltage and supply current to keep it.
It is always compromise. We have Mercedes and Ford truck in family for couple of decades.
When MB keeps voltage at 13.9-14V, Ford goes 14.5V.
So when batteries in Ford recharge faster, they usually die in 3-5 years, when we had Varta battery in MB lasting 13.
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Old 02-14-2020, 04:03 PM   #45
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Default Re: General questions about alternator charging

Quote:
Originally Posted by Graphite Dave View Post
The problem with a relay is the house battery is not charged with a charge profile that matches the battery construction. Not charged with a 3 stage charge. Bulk, Absorb, Float.

If two batteries are charged together they should be the same size, brand, type and even same manufacture date.

ACL will work but battery life is reduced.
be realistic, thats not how life works. Chassis/House batteries will 95% be different in spec. The alternator is not meant to get you charged to 100% thats what the inverter/charger, charge controllers (with a charge profile) are for. Even generators can't charge you 100%... I mean it can but it can be expensive for topping off a battery. You need this isolation relay & BIRD if you want to charge both the chassis and house battery via alternator (with priority given to the chassis battery). Once both batteries are of equal voltage tolerance the relay disconnects. Also, with a pushbutton and relay, it is a good way to jump start the chassis batteries if its low (so you can start the van), jump start the house batteries if its low (so you can start the generator)... saved my butt in many cases... its just another way to expand charge redundancies and recovery to the batteries.
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Old 02-14-2020, 04:40 PM   #46
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Default Re: General questions about alternator charging

Quote:
Originally Posted by Redridge View Post
be realistic, thats not how life works. Chassis/House batteries will 95% be different in spec. The alternator is not meant to get you charged to 100% thats what the inverter/charger, charge controllers (with a charge profile) are for. Even generators can't charge you 100%... I mean it can but it can be expensive for topping off a battery. You need this isolation relay & BIRD if you want to charge both the chassis and house battery via alternator (with priority given to the chassis battery). Once both batteries are of equal voltage tolerance the relay disconnects. Also, with a pushbutton and relay, it is a good way to jump start the chassis batteries if its low (so you can start the van), jump start the house batteries if its low (so you can start the generator)... saved my butt in many cases... its just another way to expand charge redundancies and recovery to the batteries.
I prefer to always charge the house battery with a proper 3 stage charge profile. My primary charging method is a 300 watt solar panel with a MPPT solar controller. That provides a 3 stage charge. My backup method of charging is with a vehicle powered pure sine inverter that provides "120 volt AC shore power" to the shore power charger. The shore power charger also provides a proper 3 stage charge profile.

I never directly connect the house battery to the starting battery.

My design does not allow the house battery to be used to start the vehicle. The advantage to the vehicle powered inverter design is the availability of 120 volt AC power while driving without running the house inverter that uses up house battery capacity. I can use the vehicle powered inverter to charge & power the 120 volt AC receptacles or heat shower water or power a baseboard electric heater with engine running.

I am realistic and know how life works. Multiple methods are available for charging the house batteries. All have advantages and disadvantages.
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Last edited by Graphite Dave; 02-14-2020 at 04:42 PM.
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Old 02-14-2020, 05:11 PM   #47
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Default Re: General questions about alternator charging

Quote:
Originally Posted by Graphite Dave View Post
I prefer to always charge the house battery with a proper 3 stage charge profile. My primary charging method is a 300 watt solar panel with a MPPT solar controller. That provides a 3 stage charge. My backup method of charging is with a vehicle powered pure sine inverter that provides "120 volt AC shore power" to the shore power charger. The shore power charger also provides a proper 3 stage charge profile.

I never directly connect the house battery to the starting battery.

My design does not allow the house battery to be used to start the vehicle. The advantage to the vehicle powered inverter design is the availability of 120 volt AC power while driving without running the house inverter that uses up house battery capacity. I can use the vehicle powered inverter to charge & power the 120 volt AC receptacles or heat shower water or power a baseboard electric heater with engine running.

I am realistic and know how life works. Multiple methods are available for charging the house batteries. All have advantages and disadvantages.
Im aware of solar, inverter charger setup. My comments were not general but was adding specifically to the OP original thread title "General questions about alternator charging"... hence the BIRD, isolation relay circuit links I provided, again a standard in the high end RV, MH industry. Alternators are not meant to charge batteries 100", but bulk charging is what they do best. If your solar is down, and no shore power (boondocking)... you have a 3rd way to charge your batteries with the BIRD and relay... like I said, just another redundancy to charge the batteries.
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Old 02-14-2020, 06:57 PM   #48
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Default Re: General questions about alternator charging

Thank you for re-emphasizing the VSR option.

Considering the trade-offs again, I understand that a VSR approach appears to be cheaper. But I wonder if that trade off is actually correct.

I understood the financial selling point of LiFePO4 batteries to be that throughout a longer lifetimr they end up being cheaper than AGMs.

When using LiFePO4 batteries they are typically the most expensive component of the system. Saving money on other components at the (potential?) risk of reducing the batteries' lifetime might be "penny wise and pound foolish"

On the other hand if lowering overall cost is the highest priority trade-off then I can imagine that a VSR with cheaper batteries would be reasonable.

Please let me know if I've missed or misunderstood anything.
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Old 02-14-2020, 07:00 PM   #49
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Default Re: General questions about alternator charging

Your not going to hurt a LFP pack by charging at ~13.7-14.1V through a VSR. In fact compared to some of the (slightly abusive in my view) charge profiles the drop-in MFGs recommend, it may even improve battery life some.

If you drive 50k miles a year, you might be approaching the point where the LFP pack is being "float" charged by the alternator, but thats not a common problem.
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Old 02-14-2020, 11:36 PM   #50
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Default Re: General questions about alternator charging

As I've shown, the inverter/converter setup is woefully inefficient. A more elegant way to charge the house battery from alt is to use a B2B charger.

https://www.amazon.com/Renogy-Batter...a-728968810259

I've recently installed this unit and am impressed with the results charging a LiFePO4 battery.


Quote:
Originally Posted by Graphite Dave View Post
The problem with a relay is the house battery is not charged with a charge profile that matches the battery construction. Not charged with a 3 stage charge. Bulk, Absorb, Float.

If two batteries are charged together they should be the same size, brand, type and even same manufacture date.

ACL will work but battery life is reduced.
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