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Old 12-10-2019, 20:24   #1
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Fast and safe LiFePO4 alternator charging

Hi,
I don't often post here, but I'm an appreciative visitor. Today I would like to share something. I know a lot has been said about the subject, but I'm curious what fellow cruisers think of this:
Not trying to sell anything, just interested in opinions.
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Old 13-10-2019, 22:51   #2
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Re: Fast and safe LiFePO4 alternator charging

Strange enough, if I tap the Youtube link I placed in my post above in the Cruisers Forum ap on my iPad, Youtube gives the message "Video not available" From the web view in the app it works fine, also from any browser on my PC.
Anyone any ideas why?
The link is:
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Old 14-10-2019, 05:25   #3
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Re: Fast and safe LiFePO4 alternator charging

Greetings and belated welcome aboard the CF, Walt.
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Old 15-10-2019, 09:49   #4
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Re: Fast and safe LiFePO4 alternator charging

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Originally Posted by waltdownunder View Post

Thats awesome

that enables everyone to run a small/midsized Lithium bank and charge it savely with your standard alternator.
2nd you can easly adapter current draw, so you always have the ability to safely max out of your alternator. An alternator has 50% efficeny means it creates 50% heat. So when you create 50Ax12V=1200W then the Alternator creates 1200W heat which can kills your coils if running on low RPM and cooling is missing.

With this unit if you are running on idle 1000RPM you can limit your standard 80A alternator to 25A and be safe, if you are motoring with 2000RPM you can turn it up to 40A or 50A (on a high quality one) and be safe too as the alternator can cool itself better.
Process to find your current draw limits:

Just get a cheap infrared thermometer for 10$ on aliexpress/ebay/amazon, run your alternator on different RPMs with rising current and you can easily find out how much amps your alternator can deliver at which RPM plus an overall amp limit where the alternator runs safely in all RPM ranges.

Your limit point is when the alternator temp starts not steady after running it for 2min and start to rise or above/close to the temp your isolation lacqur on the alternators coils start to melt. Eg Bosch or Delco have that data and will give it to you on request.

If they don't give you this data, crank your engine to 2800 RPM go to 60% of the rated alternators current and after 3min runtime measure the temp that is created, then lower the RPM to 2300 and measure the temp after 30 sek. runtime and then crank it immediatly up to 2800RPM again to cool it for min. 2 minutes. this 30sek time measurement is the safe max. temp point of your coils. If between that safe point and the previous measure at 2800RPM is less then 15 degrees celsius, then do the same procedure with 70% of the rated current again...your lucky and have a very good quality alternator.
Now you know your temp limit, go from idle to max. RPM in 100RPM steps and crank up the limiter till the current draw creats a steady temp 10 degrees celcius below the limit. Note all that down and you can maximise the output with given RPMs. The resulting current at idle is your overall save current draw limit and standard limit adjustment. I suggest to limit always to the current limit 300RPMs lower => when you adjust throttle the alternator never gets damaged. More RPMs never hurt, only lower.

And exactly what I was looking for my 24V big lithum bank project and the only thing that made me a headache till now=> a big balmore alternator with current limiter and temperature control cost a fortune and if breaks in remote area a lot special parts you cannot get.
With this unit I buy a cheap used big truck alternator 24V, overhaul it, do the procedure above of and it will run relaible/safe.
And a 2nd one as spare for in total for 1/3 the price of a balmore.
And if they break they can be repaired as super simple with everywhere avaliable parts. I just order 4 piece of each part I need to order for overhauling it, so I have 2 sets of spare parts if it breaks to repair myself.
Problem solved and cheap
To make the truck alternator fit adapt the ratio via the pulley of the alternator. That can be done by calculating it, so its RPM fit to the boat engines RPM. Original setup should be fare off as a truck engine is running on low rpms too. Then let a machine shop create a mounting adapter+according size pulley and ready to go.
A car alternator is insufficent, doesn't work or made to work properly. But truck works, lot boats have truck alternators as some boat engines are marinzed truck engines
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Old 16-10-2019, 01:19   #5
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Re: Fast and safe LiFePO4 alternator charging

Thank you for your reaction CaptainRivet.
You seem to know your stuff. The controller has a (software) mechanism for adjusting max Amps based on alternator RPM, but it would be better to make this a config parameter.
Rather than having a single display for setting max Amps as in the video, I will extend this to 3 displays: one for max Amps at 1000RPM, one for 2000RPM and one for 3000RPM
For other RPM values, interpolation will be used with steps of 5Amps.

The controller has its own alternator temperature sensor, with display on the LCD, so it's very easy to monitor what the temperature does at different Amps and RPMs without an extra temp meter.

Walt
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Old 16-10-2019, 03:22   #6
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Re: Fast and safe LiFePO4 alternator charging

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Originally Posted by waltdownunder View Post
Thank you for your reaction CaptainRivet.
You seem to know your stuff. The controller has a (software) mechanism for adjusting max Amps based on alternator RPM, but it would be better to make this a config parameter.
Rather than having a single display for setting max Amps as in the video, I will extend this to 3 displays: one for max Amps at 1000RPM, one for 2000RPM and one for 3000RPM
For other RPM values, interpolation will be used with steps of 5Amps.

The controller has its own alternator temperature sensor, with display on the LCD, so it's very easy to monitor what the temperature does at different Amps and RPMs without an extra temp meter.

Walt

Hi Walt,
you are welcome. Didn't realize you were the engineer behind it.
Could you make me one? And how much would it cost?
Can it run a 12V 270A or a 24V 150A alternator?

Regarding the RPM, max. setting and interpolation have a look at this diagram of a powerful heavy duty commercial 140A boat alternator (a "normal" one reaches max. 70% of its rating, this one done 95%): The vertical axle left is max current, right is % of total rated A and horizontal axle is RPM on the alternators pulley


The typical gearing ratio here would be 1:2 means the engine running 500RPM the alternator turns 1000RPM. So at 500RPM engine the 140 A alternator can deliver 20A, at 750 rpm already 80A and at 1000RPM 110A and at 1500RPM 125A and reaching its max at 2000RPM with 140A.
A 40A alternator will have a less steep curve but still exponentially. So I suggest to have 3 settings for 1000, 1500 and 2300 and adapt your steady interpolation here accordingly. Hardly any sailboater revs his engine for longer times past 2300RPM if he/she is not forced to. Would be good if the interpolation current is not fixed to 5A, better you make this configuable too. you will need different currents for the 3 steps anyhow. Fits a typical boat alternator curve much better then what you suggested.

Regarding the temp sensor: thats was one issue of the balmar units too. The sensor measuring the outside tempature at the case. Take the IR thermometer and measure the heat thats created at the spindle (there its the worst)=center of alternator. You will see especially in low RPM range a big gap between the temp your sensor measures and the spindle temprature. When the outside cast sensor shows critical temps your alternator is already permantely damaged as the inner coils lacquer reach a too high temp and started to melt. So I would implement here a offset parameter, eg. measure temp + configurable offset= core temp. Balmar corrected that and is exaclty doing that with a fixed factor, which is suboptimal as the real temp depends also on ventilation of engine room, surrounding temp of the alternator mount...
But yours is universal so it should be configuarble. THe exact offset you can measure easyly with the IR thermometer, so this take all factors into account in each individual installation.



IR-Thermometer should be on any boat, it helps you to dedect the source of overheating issues on the engine.
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