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05-07-2022, 07:51
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#16
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Nearly an old salt
Join Date: Jun 2009
Location: Lefkas Marina ,Greece
Boat: Bavaria 36
Posts: 22,801
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How to charge at a given C rate?
Take a typical 300AH Li battery , charging at 1C is extremely untypical , best might be 100A which is 0.3C
__________________
Interested in smart boat technology, networking and all things tech
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05-07-2022, 08:01
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#17
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Registered User
Join Date: Mar 2016
Location: San Francisco
Boat: Morgan 382
Posts: 2,871
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Re: How to charge at a given C rate?
Quote:
Originally Posted by Stu Jackson
I have a Balmar 612, not the newest, but Amp or Belt Manager is a feature of the regulator. RTFM???
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Unfortunately, the Balmar doesn't use a shunt. So, while you can limit the output, you can't specific or reliably limit it to a specific current. There would be some trial and error involved to determine what settings in the balmar equated to a specific c-rate.
No one has mentioned it yet, but if you want to limit current to a specific value, a DCDC charger might be the best option.
Usually charging systems in boats aren't capable of reaching higher c-rates. So, the goal isn't so much to limit, but get as much as possible in. Even limiting Alternator current via a Balmar is more about getting as much out of the alternator as you can without damaging it, vs. using a DCDC charger that will limit the current much lower than that.
__________________
-Warren
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05-07-2022, 08:24
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#18
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Registered User
Join Date: Aug 2008
Location: Sydney, Australia
Boat: Roberts 45
Posts: 1,034
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Re: How to charge at a given C rate?
Quote:
Originally Posted by goboatingnow
Take a typical 300AH Li battery , charging at 1C is extremely untypical , best might be 100A which is 0.3C
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Yes, only you're doing the math backwards, starting from the bank capacity. The OP wanted to deliberately limit the current.
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05-07-2022, 09:11
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#19
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Registered User
Join Date: Feb 2021
Location: Nomadic
Posts: 621
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Re: How to charge at a given C rate?
Yes, many quality cells can charge at 1.0C but that will shorten lifespan a fair bit.
Drop-in batteries are limited by their (usually inaccessible) internal circuitry, far lower than what the bare cells would tolerate.
Both regulators can do what you want. You need to adjust/calibrate the output as desired through actual measurement.
By default neither are "easy" to change on the fly.
Wakespeed will accept CAN signaling, so a tech person could create a micro-controlled gadget to send those commands from whatever interface you like, phone app, joystick, whatever.
Going from 0.3C to 0.5C is not going to change the impact on cell longevity that much, if that is your concern.
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05-07-2022, 09:26
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#20
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Registered User
Join Date: Nov 2019
Location: Vancouver
Boat: Ericson 27
Posts: 521
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Re: How to charge at a given C rate?
Quote:
Originally Posted by rgleason
For LFP being charged by an alternator with an external regulator, how would one adjust the alternator so that it does not exceed a certain C rate, say .25C or .3C.
For a balmar 618 or wakespeed ws500 with current sensing what would be involved in changing this setting? IE is it easy to do or a pain?
Which alternator regulator would be preferred?
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Fairly easy to pull this off with a Wakespeed. I added an extra toggle switch to my engine control panel to limit the alternator to half power, without sacrificing the alternator temperature like what happens with the balmar. (On the balmar, you signal half power by shorting out the temperature probe). It works by limiting the duty cycle.
That said, my BMS puts a cap on the charge current and communicates this via CAN BUS. The WS500 listens to this, and will limit the drive to achieve the requested value. In my case, the max charge rate for my battery is set at 120A while I only have an 85A alternator (10hp engine), so most of the time the alternator is running flat out. However, as the battery comes towards full, the BMS will command the alternator to lower its drive. Eventually, it will wind up in a state where essentially zero current is flowing into the battery and the alternator is just driving house loads.
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05-07-2022, 09:33
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#21
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Registered User
Join Date: Mar 2012
Location: Boston, MA
Boat: 1981 Bristol 32 Sloop
Posts: 17,527
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Re: How to charge at a given C rate?
Thank you Paul.
So my ocasional fast charge rate could be .5C
without much penalty in life cycles and my slower rate could be .25C
assuming the batteries and BMS are so rated.
There are indeed times when I would like to recharge at a fast rate while at the mooring, preferably at 1200 rpm or lower.
And yes the slow charge rate would be appropriate for longer motoring.
The point is that some regulator parameters need to be easily accessible.
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05-07-2022, 09:40
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#22
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Registered User
Join Date: Nov 2019
Location: Vancouver
Boat: Ericson 27
Posts: 521
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Re: How to charge at a given C rate?
Quote:
Originally Posted by rgleason
Thank you Paul.
So my ocasional fast charge rate could be .5C
without much penalty in life cycles and my slower rate could be .25C
assuming the batteries and BMS are so rated.
There are indeed times when I would like to recharge at a fast rate while at the mooring, preferably at 1200 rpm or lower.
And yes the slow charge rate would be appropriate for longer motoring.
The point is that some regulator parameters need to be easily accessible.
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So yes, this is fairly easy to do. On the balmar, you put in a toggle switch that will short out the alternator temperature probe. This will drop the field drive to 50%. Not perfect but May achieve what you want.
On the Wakespeed, you have a switch that will connect the feature-in wire to 12v or open circuit. This will limit the field to a programmable limit. I view it as the “power”/“more power” switch.
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05-07-2022, 10:06
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#23
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Registered User
Join Date: Aug 2008
Location: Sydney, Australia
Boat: Roberts 45
Posts: 1,034
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Re: How to charge at a given C rate?
Quote:
Originally Posted by hjohnson
So yes, this is fairly easy to do. On the balmar, you put in a toggle switch that will short out the alternator temperature probe. This will drop the field drive to 50%. Not perfect but May achieve what you want.
On the Wakespeed, you have a switch that will connect the feature-in wire to 12v or open circuit. This will limit the field to a programmable limit. I view it as the “power”/“more power” switch.
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Sounds like a very good solution!
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05-07-2022, 10:17
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#24
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Registered User
Join Date: Jan 2011
Location: Cowichan Bay, BC (Maple Bay Marina)
Posts: 9,704
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Re: How to charge at a given C rate?
Quote:
Originally Posted by hjohnson
So yes, this is fairly easy to do. On the balmar, you put in a toggle switch that will short out the alternator temperature probe. This will drop the field drive to 50%. Not perfect but May achieve what you want.
On the Wakespeed, you have a switch that will connect the feature-in wire to 12v or open circuit. This will limit the field to a programmable limit. I view it as the “power”/“more power” switch.
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On the Balmar, this is called Small Engine Mode (SEM). I have discussed this often on this and other boating forums.
__________________
Stu Jackson
Catalina 34 #224 (1986) C34IA Secretary
Cowichan Bay, BC, SR/FK, M25, Rocna 10 (22#) (NZ model)
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06-07-2022, 07:02
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#25
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Registered User
Join Date: Mar 2012
Location: Boston, MA
Boat: 1981 Bristol 32 Sloop
Posts: 17,527
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Re: How to charge at a given C rate?
Small Engine is a pretty rudimentary control, in my option. I had discounted it before this.
I view the Wakespeed programmable limit as much preferable. Thank you for explaining it.
Quote:
That said, my BMS puts a cap on the charge current and communicates this via CAN BUS. The WS500 listens to this, and will limit the drive to achieve the requested value. In my case, the max charge rate for my battery is set at 120A while I only have an 85A alternator (10hp engine), so most of the time the alternator is running flat out. However, as the battery comes towards full, the BMS will command the alternator to lower its drive. Eventually, it will wind up in a state where essentially zero current is flowing into the battery and the alternator is just driving house loads.
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This is just as I would expect and what I would like to do. The alternator I will use is SI28 DelcoRemy 160A brought down to 80-90A but the LFP will likely be a smaller bank.
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11-07-2022, 14:19
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#26
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Registered User
Join Date: Jun 2016
Posts: 71
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Re: How to charge at a given C rate?
Ummmmmm ......
Try installing a regulator designed to provide the desired c rate ......
Cheers!
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14-07-2022, 17:56
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#27
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Registered User
Join Date: Mar 2012
Location: Boston, MA
Boat: 1981 Bristol 32 Sloop
Posts: 17,527
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Re: How to charge at a given C rate?
I am surprised that none of you electrical gurus have come up with this answer, so I wonder if there is something wrong with it.
Put a variable DC-DC trimming converter on the field wire.
The output voltage will likely range between 13.2 and 14.3 approximately for LFP.
The External Regulator will set the upper limit of voltage and the trimming converter can be adjusted down appropriately.
So we need a Trimming DC-DC converter that will trim the voltage about 1.1-1.2 volts without too much change in the current.
Here is a calculator to determine the resistors needed.
Vicor Design Calculators
See Output voltage trimming
https://www.vicorpower.com/documents...00_Sect_05.pdf
https://www.vicorpower.com/dc-dc/iso...-dc-converters
https://nortonsafe.search.ask.com/we...doi=2021-10-19
Unfortunately these are too expensive.
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14-07-2022, 22:34
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#28
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Registered User
Join Date: Aug 2008
Location: Sydney, Australia
Boat: Roberts 45
Posts: 1,034
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Re: How to charge at a given C rate?
Quote:
Originally Posted by rgleason
I am surprised that none of you electrical gurus have come up with this answer, so I wonder if there is something wrong with it.
Put a variable DC-DC trimming converter on the field wire.
The output voltage will likely range between 13.2 and 14.3 approximately for LFP.
[...]
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The question was how to adjust the alternator to limit the output current. Not sure what sort of DC-DC converter you want to use to limit currents of around 100A or more?
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15-07-2022, 02:44
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#29
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Registered User
Join Date: Mar 2012
Location: Boston, MA
Boat: 1981 Bristol 32 Sloop
Posts: 17,527
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Re: How to charge at a given C rate?
Quote:
Originally Posted by hzcruiser
The question was how to adjust the alternator to limit the output current. Not sure what sort of DC-DC converter you want to use to limit currents of around 100A or more?
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Its the alternator field wire that is being adjusted, to change C.
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15-07-2022, 06:59
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#30
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Registered User
Join Date: Feb 2021
Location: Nomadic
Posts: 621
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Re: How to charge at a given C rate?
The load determines the current pulled
up to whatever the source makes available.
Current cannot be pushed given a fixed voltage.
Varying the voltage output will indirectly influence the current pulled, but that relationship will vary with SoC.
Usually the goal is to reach say 13.75V at the posts as quickly as possible, say in under a couple hours, and the issue with LFP charged by alternator is preventing the current from exceeding what is healthy.
That is, if YOU need to get to Full, the bank does not.
Lead never has that current problem, the bank DOES need to get to 100% Full, and you need at least a 5-hour charge cycle to get there, even if 2C is available the whole time.
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