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03-03-2023, 16:19
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#76
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Senior Cruiser
Join Date: Sep 2014
Location: puget sound washington
Boat: 1968 Islander bahama 24 hull 182, 1963 columbia 29 defender. hull # 60
Posts: 12,121
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Re: DC to DC charger - not needed for boats with proper alternators.
Quote:
Originally Posted by Fuss
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??
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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 .
__________________
Non illigitamus carborundum
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03-03-2023, 16:29
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#77
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Registered User
Join Date: Sep 2019
Location: Lifeaboard
Boat: FP Lavezzi 40
Posts: 2,839
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Re: DC to DC charger - not needed for boats with proper alternators.
Quote:
Originally Posted by newhaul
Here is my system westerbeke 10- two 75 amp stock alternator ( cost new $45 for it)
40 amp DC/DC . ( $130) 250ah lifepo4 600 watts solar mppt controller.
Alternator is actually the #3 backup charge source. Only used for about 45 minutes getting into or out of a marina or Anchorage.
Show me a fit for purpose alternator that can handle a full .75C output that costs less than stock and DC/DC . That will fit in my engine space on my 29 ft sailboat.
Every installation is different .
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what 40A dc2DC for 130$ do you use, renogy?
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03-03-2023, 16:42
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#78
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Senior Cruiser
Join Date: Sep 2014
Location: puget sound washington
Boat: 1968 Islander bahama 24 hull 182, 1963 columbia 29 defender. hull # 60
Posts: 12,121
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Re: DC to DC charger - not needed for boats with proper alternators.
Quote:
Originally Posted by CaptainRivet
what 40A dc2DC for 130$ do you use, renogy?
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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
__________________
Non illigitamus carborundum
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20-06-2023, 13:38
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#79
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Registered User
Join Date: Jun 2016
Location: Australia
Boat: Milkraft 60 ex trawler
Posts: 4,653
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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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20-06-2023, 14:17
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#80
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Registered User
Join Date: Nov 2019
Location: Vancouver
Boat: Ericson 27
Posts: 521
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Re: DC to DC charger - not needed for boats with proper alternators.
Quote:
Originally Posted by Simi 60
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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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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20-06-2023, 14:28
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#81
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Registered User
Join Date: Jun 2016
Location: Australia
Boat: Milkraft 60 ex trawler
Posts: 4,653
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Re: DC to DC charger - not needed for boats with proper alternators.
Quote:
Originally Posted by hjohnson
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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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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20-06-2023, 14:36
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#82
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Registered User
Join Date: Nov 2019
Location: Vancouver
Boat: Ericson 27
Posts: 521
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Re: DC to DC charger - not needed for boats with proper alternators.
Quote:
Originally Posted by Simi 60
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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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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20-06-2023, 14:39
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#83
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Senior Cruiser
Join Date: Sep 2014
Location: puget sound washington
Boat: 1968 Islander bahama 24 hull 182, 1963 columbia 29 defender. hull # 60
Posts: 12,121
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Re: DC to DC charger - not needed for boats with proper alternators.
Quote:
Originally Posted by Simi 60
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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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.
__________________
Non illigitamus carborundum
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20-06-2023, 14:51
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#84
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Registered User
Join Date: Jun 2016
Location: Australia
Boat: Milkraft 60 ex trawler
Posts: 4,653
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Re: DC to DC charger - not needed for boats with proper alternators.
Quote:
Originally Posted by newhaul
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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It's an 840ah @ 24v bank and we use around 25amps when underway so feasibly several hours at a time
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20-06-2023, 14:51
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#85
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Registered User
Join Date: Nov 2019
Location: Vancouver
Boat: Ericson 27
Posts: 521
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Re: DC to DC charger - not needed for boats with proper alternators.
Quote:
Originally Posted by newhaul
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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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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20-06-2023, 14:53
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#86
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Registered User
Join Date: Jun 2016
Location: Australia
Boat: Milkraft 60 ex trawler
Posts: 4,653
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Re: DC to DC charger - not needed for boats with proper alternators.
Quote:
Originally Posted by hjohnson
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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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.
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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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20-06-2023, 14:59
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#87
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Senior Cruiser
Join Date: Sep 2014
Location: puget sound washington
Boat: 1968 Islander bahama 24 hull 182, 1963 columbia 29 defender. hull # 60
Posts: 12,121
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Re: DC to DC charger - not needed for boats with proper alternators.
Quote:
Originally Posted by hjohnson
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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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
__________________
Non illigitamus carborundum
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20-06-2023, 15:03
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#88
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Registered User
Join Date: Nov 2019
Location: Vancouver
Boat: Ericson 27
Posts: 521
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Re: DC to DC charger - not needed for boats with proper alternators.
Quote:
Originally Posted by Simi 60
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)
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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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20-06-2023, 15:05
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#89
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Senior Cruiser
Join Date: Sep 2014
Location: puget sound washington
Boat: 1968 Islander bahama 24 hull 182, 1963 columbia 29 defender. hull # 60
Posts: 12,121
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Re: DC to DC charger - not needed for boats with proper alternators.
Quote:
Originally Posted by hjohnson
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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One question why no solar on a sailboat? My 200 watts charges me right up .
__________________
Non illigitamus carborundum
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20-06-2023, 15:06
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#90
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Registered User
Join Date: Sep 2019
Location: Lifeaboard
Boat: FP Lavezzi 40
Posts: 2,839
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Re: DC to DC charger - not needed for boats with proper alternators.
Quote:
Originally Posted by Simi 60
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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Correct either DC2DC or smart reg, both makes no sense.
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