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Old 03-03-2023, 16:19   #76
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Re: DC to DC charger - not needed for boats with proper alternators.

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Originally Posted by Fuss View Post
I'm thinking that these DC DC chargers are just there for boats with alternators that cannot handle running at full output.


Thats ok I guess, but for boats with high quality industrial large frame alternators then they don't need them and they can put their full charge into lithium without wasting their time and money on these compromise devices.


I see now that Battleborn has some funny shaped green device that they are promoting that gives your alternator a rest every 20 minutes.



Really, instead of this and these DC to DC chargers should we not be promoting decent high quality fit for purpose alternators first??
Here is my system westerbeke 10- two 75 amp stock alternator ( cost new $45 for it)
40 amp DC/DC . ( $130) 250ah lifepo4 600 watts solar mppt controller.

Alternator is actually the #3 backup charge source. Only used for about 45 minutes getting into or out of a marina or Anchorage.
Show me a fit for purpose alternator that can handle a full .75C output that costs less than stock and DC/DC . That will fit in my engine space on my 29 ft sailboat.

Every installation is different .
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Old 03-03-2023, 16:29   #77
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Re: DC to DC charger - not needed for boats with proper alternators.

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Originally Posted by newhaul View Post
Here is my system westerbeke 10- two 75 amp stock alternator ( cost new $45 for it)
40 amp DC/DC . ( $130) 250ah lifepo4 600 watts solar mppt controller.

Alternator is actually the #3 backup charge source. Only used for about 45 minutes getting into or out of a marina or Anchorage.
Show me a fit for purpose alternator that can handle a full .75C output that costs less than stock and DC/DC . That will fit in my engine space on my 29 ft sailboat.

Every installation is different .

what 40A dc2DC for 130$ do you use, renogy?
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Old 03-03-2023, 16:42   #78
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Re: DC to DC charger - not needed for boats with proper alternators.

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what 40A dc2DC for 130$ do you use, renogy?
Yes a renogy 40 via Amazon prime
https://www.amazon.com/Renogy-Batter...715066929&th=1

Just Google today's price I paid 120 on sale
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Old 20-06-2023, 13:38   #79
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Re: DC to DC charger - not needed for boats with proper alternators.

I still don't get this DC to DC charger saving the alt.

I am looking at fitting a 36si Delco Remy 105 amp @ 24v to our engine
At our 1150 cruise RPM there is 3800rpm at the pulley so we should be seeing 80amps.

Sterling 24v 35 amp DC to DC chargers X 2 is 70 amps pulling from the starts and alt.
Surely that'll still smoke the alternator if running for hour after hour after hour
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Old 20-06-2023, 14:17   #80
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Re: DC to DC charger - not needed for boats with proper alternators.

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Originally Posted by Simi 60 View Post
I still don't get this DC to DC charger saving the alt.

I am looking at fitting a 36si Delco Remy 105 amp @ 24v to our engine
At our 1150 cruise RPM there is 3800rpm at the pulley so we should be seeing 80amps.

Sterling 24v 35 amp DC to DC chargers X 2 is 70 amps pulling from the starts and alt.
Surely that'll still smoke the alternator if running for hour after hour after hour
People make this claim based on two reasons.

1. They’re typically only putting in, say, a 30A DC-DC charger, or otherwise sizing the converter so they aren’t stressing the alternator. So, maybe, they’ll limit themselves to 60A charging on a 120A alternator.

2. They haven’t designed their system properly to avoid a high voltage disconnect, and a DC-DC is much less sensitive to a battery disconnect compared to the alternator.

Neither of these are an issue when you have an integrated system with a smart regulator. If my alternator gets too hot, the regulator backs off the field current to let it cool down. If the BMS throws a warning or alarm, the regulator kills the field long before the disconnect might happen.
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Old 20-06-2023, 14:28   #81
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Re: DC to DC charger - not needed for boats with proper alternators.

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Originally Posted by hjohnson View Post
People make this claim based on two reasons.

1. They’re typically only putting in, say, a 30A DC-DC charger, or otherwise sizing the converter so they aren’t stressing the alternator. So, maybe, they’ll limit themselves to 60A charging on a 120A alternator.

2. They haven’t designed their system properly to avoid a high voltage disconnect, and a DC-DC is much less sensitive to a battery disconnect compared to the alternator.

Neither of these are an issue when you have an integrated system with a smart regulator. If my alternator gets too hot, the regulator backs off the field current to let it cool down. If the BMS throws a warning or alarm, the regulator kills the field long before the disconnect might happen.

But if I have a smart regulator why would I need DC- DC chargers?

I thought the whole idea of smart regs like the Balmar or Wakespeed was so I could charge from alt direct to Lifepo4 bank?
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Old 20-06-2023, 14:36   #82
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Re: DC to DC charger - not needed for boats with proper alternators.

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But if I have a smart regulator why would I need DC- DC chargers?

I thought the whole idea of smart regs like the Balmar or Wakespeed was so I could charge from alt direct to Lifepo4 bank?
Exactly my point. The only reason to use a DC-DC is if you’re using an internally regulated alternator. If you have a smart regulator, plug that bastard straight into the LFP bank.

I’ve got a WS500, and it communicates over CANBus with my BMS and victron setup, and works a treat. I do have a DC-DC charger in my system, but it’s just a little 18A unit that keeps my starting battery happy.
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Old 20-06-2023, 14:39   #83
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Re: DC to DC charger - not needed for boats with proper alternators.

Quote:
Originally Posted by Simi 60 View Post
I still don't get this DC to DC charger saving the alt.

I am looking at fitting a 36si Delco Remy 105 amp @ 24v to our engine
At our 1150 cruise RPM there is 3800rpm at the pulley so we should be seeing 80amps.

Sterling 24v 35 amp DC to DC chargers X 2 is 70 amps pulling from the starts and alt.
Surely that'll still smoke the alternator if running for hour after hour after hour
Let's see 70 amps out of a 105 amp alternator is approx 68% of total possible . So you are derating the alternator by just over 30% which reduces the heat considerably. And at 3800rpm there is plenty of cooling air to keep the alternator from overheating.
Aside from how long do you actually think the 70amp output would really be needed.
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Old 20-06-2023, 14:51   #84
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Re: DC to DC charger - not needed for boats with proper alternators.

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Let's see 70 amps out of a 105 amp alternator is approx 68% of total possible . So you are derating the alternator by just over 30% which reduces the heat considerably. And at 3800rpm there is plenty of cooling air to keep the alternator from overheating.
Aside from how long do you actually think the 70amp output would really be needed.
It's an 840ah @ 24v bank and we use around 25amps when underway so feasibly several hours at a time
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Old 20-06-2023, 14:51   #85
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Re: DC to DC charger - not needed for boats with proper alternators.

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Originally Posted by newhaul View Post
Let's see 70 amps out of a 105 amp alternator is approx 68% of total possible . So you are derating the alternator by just over 30% which reduces the heat considerably. And at 3800rpm there is plenty of cooling air to keep the alternator from overheating.
Aside from how long do you actually think the 70amp output would really be needed.
Right, but you’re better off just letting an advanced regulator derate as needed to keep the alternator within acceptable temperature ranges. I can actually pull 70A out of my 85A hitachi alternator all day long, but mostly because it has excellent airflow (no heat exchanger/exhaust manifold on my 1GM10).

As far as how often I need that? Well, if I’ve been hanging out on the hook for three days and am 250Ah down, we’re looking at three and a half hours at 70A to replenish the battery.

Now that said, I usually run the alternator at half power so that I can actually make hull speed.
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Old 20-06-2023, 14:53   #86
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Re: DC to DC charger - not needed for boats with proper alternators.

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Originally Posted by hjohnson View Post
Exactly my point. The only reason to use a DC-DC is if you’re using an internally regulated alternator. If you have a smart regulator, plug that bastard straight into the LFP bank.

I’ve got a WS500, and it communicates over CANBus with my BMS and victron setup, and works a treat. I do have a DC-DC charger in my system, but it’s just a little 18A unit that keeps my starting battery happy.
Cool and as I suspected
Next part of the mystery is I see mention of modifying the alt so internal reg is no more.
Is that required or does the WS500 negate the need?

Quote:
. I do have a DC-DC charger in my system, but it’s just a little 18A unit that keeps my starting battery happy.
So it's not smart enough to do starts first then go to house?
What about if we have a Victron VSR installed? (We have one from a prior failed experiment)
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Old 20-06-2023, 14:59   #87
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Re: DC to DC charger - not needed for boats with proper alternators.

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Originally Posted by hjohnson View Post
Right, but you’re better off just letting an advanced regulator derate as needed to keep the alternator within acceptable temperature ranges. I can actually pull 70A out of my 85A hitachi alternator all day long, but mostly because it has excellent airflow (no heat exchanger/exhaust manifold on my 1GM10).

As far as how often I need that? Well, if I’ve been hanging out on the hook for three days and am 250Ah down, we’re looking at three and a half hours at 70A to replenish the battery.

Now that said, I usually run the alternator at half power so that I can actually make hull speed.
Sounds kind of like me I pull 40 apms out of my 75 amp 12v alternator all day on my 10-2 but have a kill switch in the sense wire so I can use the whole 12hp when needed .
Renogy 40amp b2b
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Old 20-06-2023, 15:03   #88
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Re: DC to DC charger - not needed for boats with proper alternators.

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Originally Posted by Simi 60 View Post
Cool and as I suspected
Next part of the mystery is I see mention of modifying the alt so internal reg is no more.
Is that required or does the WS500 negate the need?


So it's not smart enough to do starts first then go to house?
What about if we have a Victron VSR installed? (We have one from a prior failed experiment)
You’ll need to modify the alternator. The modification is fairly trivial, but it does involve opening it up and adding wires. Basically, you open it up, find where the internal regulator connects to the brushes and bring that out. For my alternator, I just took the whole unit to my local alternator shop and had them do the modification for me. They also replaced the bearings, upratef the rectifier, and generally rebuilt it, for something like $150. Money well spent imho.

I went with the 18A DC to DC mostly because the charge profiles are significantly different between lead acid and lfp. My Marine Start battery lives on the float voltage of 13.8V no matter what my house battery is doing. I often let the house drift down to 13.2V when not using the boat. But maintenance free Lead Acids love to live on the float. So it does.
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Old 20-06-2023, 15:05   #89
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Re: DC to DC charger - not needed for boats with proper alternators.

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Originally Posted by hjohnson View Post
Right, but you’re better off just letting an advanced regulator derate as needed to keep the alternator within acceptable temperature ranges. I can actually pull 70A out of my 85A hitachi alternator all day long, but mostly because it has excellent airflow (no heat exchanger/exhaust manifold on my 1GM10).

As far as how often I need that? Well, if I’ve been hanging out on the hook for three days and am 250Ah down, we’re looking at three and a half hours at 70A to replenish the battery.

Now that said, I usually run the alternator at half power so that I can actually make hull speed.
One question why no solar on a sailboat? My 200 watts charges me right up .
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Old 20-06-2023, 15:06   #90
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Re: DC to DC charger - not needed for boats with proper alternators.

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Originally Posted by Simi 60 View Post
But if I have a smart regulator why would I need DC- DC chargers?

I thought the whole idea of smart regs like the Balmar or Wakespeed was so I could charge from alt direct to Lifepo4 bank?
Correct either DC2DC or smart reg, both makes no sense.
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