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Old 04-07-2022, 15:34   #1
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How to charge at a given C rate?

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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Old 04-07-2022, 15:38   #2
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Re: How to charge at a given C rate?

Both can be set to a maximum current ( tapered by temperature etc ) though usually unless you have a really big alternator or a small LFP bank , you’ll be limited by the alternator temperature , belt and or engine loading , the actual output from small case alternators is nothing like the plate suggests.

Hence say on a typical 70 A small case the best you might get is 40 A continuous , this is a very small “ C” for a typical 300+ AH LFP battery.
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Old 04-07-2022, 16:05   #3
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Re: How to charge at a given C rate?

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Originally Posted by rgleason View Post
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?

I have a Balmar 612, not the newest, but Amp or Belt Manager is a feature of the regulator. RTFM???
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Old 04-07-2022, 16:36   #4
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Re: How to charge at a given C rate?

Perhaps I. did not explain clearly or ask the right question.
Alternator modified Delco Remy SI28 large truck alternator with adequate serpentine pulley ratios to get the alt rpm up high enough for good cooling, plus exhaust fan directly above.
External regulation through belt manager will be adjusted down to approximate, what would be .3C for a 200ah or 300ah LFP bank, which is 60amp, or 90amps.

Is it just belt manager that would control the alternator current? No I don't think so, for the wakespeed, I think it could be controled by the sensed current in the shunt, as long as the LFP charge parameters are met.

I don' t know how these things are programmed yet or if it is difficult to change.

Most of the time I would like to charge at .25C and ocassionaly at .3C. It would be nice if that setting was easy to change.

Am I misunderstanding something about the ready acceptance of LFP and the knees at either end of the curve? Perhaps these batteries being made of individual cells that are somewhat different, might create an issue with these charge rates, but I think the BMS should handle that.
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Old 04-07-2022, 16:41   #5
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Re: How to charge at a given C rate?

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Originally Posted by rgleason View Post
Perhaps I. did not explain clearly or ask the right question.
Alternator modified Delco Remy SI28 large truck alternator with adequate serpentine pulley ratios to get the alt rpm up high enough for good cooling, plus exhaust fan directly above.
External regulation through belt manager will be adjusted down to approximate, what would be .3C for a 200ah or 300ah LFP bank, which is 60amp, or 90amps.

Is it just belt manager that would control the alternator current? No I don't think so, for the wakespeed, I think it could be controled by the sensed current in the shunt, as long as the LFP charge parameters are met.

I don' t know how these things are programmed yet or if it is difficult to change.

Most of the time I would like to charge at .25C and ocassionaly at .3C. It would be nice if that setting was easy to change.

Am I misunderstanding something about the ready acceptance of LFP and the knees at either end of the curve? Perhaps these batteries being made of individual cells that are somewhat different, might create an issue with these charge rates, but I think the BMS should handle that.
RTFM , both can do what you want in different ways the wakespeed is very configurable but the configuration tools are poor
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Old 04-07-2022, 17:03   #6
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Re: How to charge at a given C rate?

I have a Balmar 612, and reading the manual the 618 looks similar. The belt manager controls percent of full output, but that is not a fixed amp rating. I am pretty sure they are completely unaware of output current, and most certainly unaware of how much of that current goes to the battery.
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Old 04-07-2022, 17:25   #7
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Re: How to charge at a given C rate?

For Balmar, I believe the belt manager limits the maximum field current which is related to, but not the same as output current.

For wakespeed, goboat you are right rtfm.

For LFP, charging at say .3C could that be done (poorly) by targeting a certain voltage or should it be done by measuring current, I am talking about while the LFP are in bulk mode and not at the "high knee".

I dont think changing the charge rate will be easy for either regulator, but I need to read.
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Old 05-07-2022, 00:35   #8
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Re: How to charge at a given C rate?

on the balmar you use the belt manager. or now called the field manager on the 618

stick an inverter load on the battery bigger then the alt (ie 1500w heater) rev engine to 2000rpm. and measure alt with clamp meter. adjust belt manager down untill you see the alt amps you want. (start with it already down if you want then bring up)

that will set max alt current. there is no way to set max batt current. IE if you have big loads the alt will not increase to max battery amps. so set alt amps at battery amps wanted +avg load


I'm not sure why you want your c rate so low. I would just set to -10% for a bit less alt heat and let the batteries take it all. might as well just buy agm if only charging at .3c
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Old 05-07-2022, 01:07   #9
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Re: How to charge at a given C rate?

If you have CanBUS from your BMS then the Wakespeed allows more control as you can simply set a maximum charge current. Otherwise, as described above either regulatorís belt manager is a rougher but effective way to throttle output.
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Old 05-07-2022, 01:24   #10
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Re: How to charge at a given C rate?

The balmar unit can be set to limit the field current, this in turn will limit the output current. ( this is in belt manager). This is a fairly crude but effective way to limit output. To relate this to charge current would require you to measure the resulting charge current and adjust to suit.
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Old 05-07-2022, 01:29   #11
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Re: How to charge at a given C rate?

Quote:
Originally Posted by rgleason View Post
Perhaps I. did not explain clearly or ask the right question.
Alternator modified Delco Remy SI28 large truck alternator with adequate serpentine pulley ratios to get the alt rpm up high enough for good cooling, plus exhaust fan directly above.
External regulation through belt manager will be adjusted down to approximate, what would be .3C for a 200ah or 300ah LFP bank, which is 60amp, or 90amps.

Is it just belt manager that would control the alternator current? No I don't think so, for the wakespeed, I think it could be controled by the sensed current in the shunt, as long as the LFP charge parameters are met.

I don' t know how these things are programmed yet or if it is difficult to change.

Most of the time I would like to charge at .25C and ocassionaly at .3C. It would be nice if that setting was easy to change.

Am I misunderstanding something about the ready acceptance of LFP and the knees at either end of the curve? Perhaps these batteries being made of individual cells that are somewhat different, might create an issue with these charge rates, but I think the BMS should handle that.


The wavespeed has a current sensor so it can be adjusted fairly accurately

The balmar has no direct current sensing , so you have to use the field adjust setting to limit output. If you use a suitable current meter you can tweak the field percentage to roughly deliver the required maximum current.

Once you stay within the C limits specified for the battery and obey the upper voltage limits etc you can charge the Li at any intervening C. Lower fractional c is better then higher in general recharge little and often is best for lithium
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Old 05-07-2022, 04:59   #12
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Re: How to charge at a given C rate?

Yes, that is a good point, there is the advanced program parameter for field current for Balmar. I expect wakespeed has something similar.

So the max charge current can be set for both regulators, to an approximate value for Balmar and a more precise value for Wakespeed.

I was hoping to be able to change this value easily, from some faster C rate to a slower C rate, depending on needs and conditions. Neither regulator makes this very easy, because they assume set and forget.

Using a magnet into advanced mode is somewhat clunky. Uploading batch files to the wakespeed with pc attached.


PS thanks for all the good points.

I hesitate to ask what charging rates are reasinable, but some real world examples would be useful. With battery manfacturer and BMS used, please.
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Old 05-07-2022, 05:10   #13
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Re: How to charge at a given C rate?

Most LifePO can be charged at 1C so I don't see the problem ?
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Old 05-07-2022, 05:37   #14
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Re: How to charge at a given C rate?

The Balmar 618 is very easy to adjust and set the various parameters, if you get a smart shunt and the Blue Tooth connection. There is an app that can be used to set the parameters and give real time data on the Alternator's temperature and output.
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Old 05-07-2022, 07:28   #15
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Re: How to charge at a given C rate?

yes, 0.3C is a relatively low rate, but as you said, ideally you want a smart alternator that you can tell "I want to focus on charging the batts quickly" or "go easy mate, as we'll have to motor for a long time today"

Then again, keeping the charge rate at around 1C or a bit lower seems to be the sweet spot even if you would waste some energy on long motoring days.

Even a "smart alternator" cannot predict how long you're going to run the engine, right?

Then again, you could think of this: if the engine is just above idle, I just want to charge the batts, if the engine is revving much higher, I'm motoring. Then the smart alternator could pick up on that.

Or the alternator could pick up on whether the engine is in neutral or not?
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