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Old 02-15-2020, 02:43 PM   #51
Graphite Dave
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Default Re: General questions about alternator charging

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Originally Posted by calbiker View Post
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.
You are correct that going from 12 volt DC to 120 volt AC and then back to 12 volt DC is not efficient. Do not know if I would call it woefully.

In my case the charging by the vehicle powered inverter is seldom used because the primary method of charging is the 300 watt solar panel in my climate. Vehicle powered inverter powering the shore power charging is the backup to the primary charging method. Efficiency is not important when system is not used very often. In addition do I really care how efficient the design is? Doubt very much I can measure the difference in fuel economy when the alternator has to run for a bit longer.

How does a B2B work? Does it convert the vehicle DC power to AC and then produce the proper DC output for charging? Is the design the same as a vehicle powered inverter powering a DC charger? Only difference is the vehicle powered inverter also provides access to the AC power when driving?

Wonder what the efficiency is for a B2B. Is it significantly different than the vehicle powered inverter powering a shore power charger?

Obviously the B2B is a viable solution that is better than an ACL because it provides a proper charge profile as does the vehicle powered inverter powering the shore power charger.

I do use the 120 volt AC power available with engine running regularly for other uses.
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Old 02-15-2020, 04:30 PM   #52
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Default Re: General questions about alternator charging

Efficiency is woeful when the alternator needs to supply 60A to the converter that charges at 30A. That's 50% efficient.

A B2B is about 85% efficient and a lot cheaper.
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Old 02-15-2020, 04:39 PM   #53
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Default Re: General questions about alternator charging

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Efficiency is woeful when the alternator needs to supply 60A to the converter that charges at 30A. That's 50% efficient.

A B2B is about 85% efficient and a lot cheaper.
How did you arrive at that percentage?

In the case of my build....the wire run from the Cyrix to the house batteries is about 18 feet. It is 2awg wire. If that run was 120v....there would be some efficiency gains there.
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Old 02-15-2020, 05:32 PM   #54
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Default Re: General questions about alternator charging

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Originally Posted by calbiker View Post
Efficiency is woeful when the alternator needs to supply 60A to the converter that charges at 30A. That's 50% efficient.

A B2B is about 85% efficient and a lot cheaper.
Doubt very much that you can lose 30 amps in the process. Sure would get warm in the van with that much power being dissipated as heat.

The vehicle powered inverter is about the same efficiency as the B2B. The added efficiency loss is in the shore power charger which I would guess is about 85% efficient. So maybe vehicle powered inverter powering a shore power charger is about 15% less efficient? As I said I doubt that I could measure the change in fuel usage attributed to the charger efficiency.

Cost of the two systems is about the same when you already have a shore power charger.
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Old 02-15-2020, 06:13 PM   #55
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Default Re: General questions about alternator charging

I use the alternator/Aux Batt/Inverter/Shore Charger set up and find it works great! Don't care about efficiency as I only use this while highway driving. I like it because it allows me to shore power charge when shore power is available. I also like that the Aux Battery buffers the alternator while at idle. I don't see a down side to this method of charging perhaps someone else will...
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Old 02-15-2020, 06:37 PM   #56
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Default Re: General questions about alternator charging

I provided data about my AC charger's efficiency above and the calbiker's 50% efficiency nunber is roughly correct. I have not found it affecting fuel economy yet for a v6 NCV3

For a 1000 watt renogy inverter the price I paid was the same as a 40 amp B2B charger from Renogy. (And perhaps a little less considering the negligible wire costs) I have the house charger set to charge at about 30 amps and it works well.

There is one othrrt trade off that I was unaware of before and will keep in mind for the future:

With a Renogy inverter/charger combo, one cannot invert and charge at the same time. So I cannot use the house inverter when the vehicle is charging the house batteries. The house inverter charger combo would either a) invert but not charge until the battery voltage is low to switch functions b) transfer the AC loads to the vehicle AC source (as if it's unlimited shore power )

Had I been conscious of this limitation, I might have purchased two separate inverter and charger devices for the house side... Or a B2B charger for alternator charging. You live and you try stuff and you learn

Last edited by SeattleNewbie; 02-15-2020 at 06:40 PM.
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Old 02-15-2020, 07:48 PM   #57
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Default Re: General questions about alternator charging

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Originally Posted by SeattleNewbie View Post
I provided data about my AC charger's efficiency above and the calbiker's 50% efficiency nunber is roughly correct. I have not found it affecting fuel economy yet for a v6 NCV3

For a 1000 watt renogy inverter the price I paid was the same as a 40 amp B2B charger from Renogy. (And perhaps a little less considering the negligible wire costs) I have the house charger set to charge at about 30 amps and it works well.

There is one othrrt trade off that I was unaware of before and will keep in mind for the future:

With a Renogy inverter/charger combo, one cannot invert and charge at the same time. So I cannot use the house inverter when the vehicle is charging the house batteries. The house inverter charger combo would either a) invert but not charge until the battery voltage is low to switch functions b) transfer the AC loads to the vehicle AC source (as if it's unlimited shore power )

Had I been conscious of this limitation, I might have purchased two separate inverter and charger devices for the house side... Or a B2B charger for alternator charging. You live and you try stuff and you learn
When I have the vehicle powered inverter supplying power to the house Magnum inverter/charger/transfer switch the 120 volt AC duplex plugs in the van are powered. Unit charges at the same time recepticals are powered. The Magnum, when on, powers the same recepticals when Magnum is powered by the house battery. No need to run the Magnum when power is supplied by the vehicle powered inverter.
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Old 02-15-2020, 08:04 PM   #58
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Default Re: General questions about alternator charging

You need to understand power factor. Here's an excellent video. The first few minutes of viewing is good enough. A circuit with a PF=1 has a sinusoidal current waveform. This is not the case with a peak charge circuit (a diode rectifier charging a capacitor). AC current only flows when capacitor voltage is less than the AC voltage. The resulting current waveform looks like spikes. That's what you'll see with converters. They typically have a PF = 0.7 if not PF corrected.



Let's give an example. There's a 3-stage converter rated for 30A at 14.7V with 80% efficiency. The inverter has 90% efficiency and the alternator voltage is 13.7V. What's the system efficiency?

Alt output current = 30A * (14.7V/13.7V) / (0.7 * 0.8 * 0.9) = 64.4A

Alt power = 13.7V * 64.4A = 882W
Converter output power = 14.7V * 30A = 441W

System efficiency = 441W/882W = 50%

Quote:
Originally Posted by Graphite Dave View Post
Doubt very much that you can lose 30 amps in the process. Sure would get warm in the van with that much power being dissipated as heat.

The vehicle powered inverter is about the same efficiency as the B2B. The added efficiency loss is in the shore power charger which I would guess is about 85% efficient. So maybe vehicle powered inverter powering a shore power charger is about 15% less efficient? As I said I doubt that I could measure the change in fuel usage attributed to the charger efficiency.

Cost of the two systems is about the same when you already have a shore power charger.
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Old 02-15-2020, 08:10 PM   #59
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Default Re: General questions about alternator charging

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Originally Posted by Graphite Dave View Post
When I have the vehicle powered inverter supplying power to the house Magnum inverter/charger/transfer switch the 120 volt AC duplex plugs in the van are powered. Unit charges at the same time recepticals are powered. The Magnum, when on, powers the same recepticals when Magnum is powered by the house battery. No need to run the Magnum when power is supplied by the vehicle powered inverter.
I understand. That is how mine works too: When charging from the alternator, the 1000 watt vehicle inverter supplies power to all AC loads.

My need to use the 2000 watt house inverter is due to a poor earlier experimental decision of installing a 1440 watt water heater. that water heater needs to be replaced with a more long term solution.
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