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Old 11-01-2020, 02:29   #1
rom
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Alternator voltage sense

Hi, I am using the voltage sense wire of my 28SI alternators. It is a positive cable directly connected to the battery terminal, small section, fused 1A. Sounds good except it does not compensate for the negative circuit losses, only the positive side. Well, though the negative side usually accounts for a big half of the losses (due to additional switches & fuses on that side) I am only charging at about 14V instead of 14.5V. A little better when battery is almost full and amps decreases. It is my understanding that other VR like balmar also use a single positive sense wire. Victron OTOH seems to be using a positive AND a negative sense wires. Any thoughts ?
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Old 11-01-2020, 04:39   #2
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Re: Alternator voltage sense

http://www.delcoremy.com/documents/a...24si-28si.aspx


Why Remote Sense? | Delco Remy


Hello Rom, are you connecting sense to the battery terminal of the alternator or to the terminal of the battery? If looped back to the alternator, one is defeating the remote sensing function by monitoring the alternator instead of the battery. I do not see Delco Remy calling out a fuse on the sense line. It is also mentioned that the 28SI alternator can function without the sense or indicator or relay terminals being used.
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Old 11-01-2020, 07:03   #3
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Re: Alternator voltage sense

I think that the newer revisions of the Balmar regulator instructions say that the -12v wire from the regulator should be connected "as close to the -12v battery post as possible." I think that MaineSail also suggests this, too. Otherwise you just have to make sure that you’ve got a really low-loss battery charging system, because most of the other chargers won’t actually measure voltage at the battery. IMO, you should eliminate all the losses first and only then try to compensate for whatever losses are left.
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Old 11-01-2020, 07:37   #4
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Re: Alternator voltage sense

You are correct. For Balmar MC-614 Regulator sensing wires

  • Reg + direct to House battery
  • Reg - direct to House battery (or through shunt to battery, not preferred I believe)
  • Assuming the House battery is the bank being charged.
  • Assuming a remote sensing Regulator like the Balmar MC-614, (but the right wiring for ACRS Regulator is similar)
https://marinehowto.com/alternators-voltage-sensing/



Quote:
Originally Posted by Bycrick View Post
I think that the newer revisions of the Balmar regulator instructions say that the -12v wire from the regulator should be connected "as close to the -12v battery post as possible." I think that MaineSail also suggests this, too. Otherwise you just have to make sure that you’ve got a really low-loss battery charging system, because most of the other chargers won’t actually measure voltage at the battery. IMO, you should eliminate all the losses first and only then try to compensate for whatever losses are left.
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Old 11-01-2020, 07:57   #5
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Re: Alternator voltage sense

Sorry if I diluted the conversation with stock 28SI information if indeed Rom is running an externally regulated system.
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Old 11-01-2020, 08:48   #6
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Re: Alternator voltage sense

Quote:
Originally Posted by Spot View Post
Sorry if I diluted the conversation with stock 28SI information if indeed Rom is running an externally regulated system.

No worries, thank you for the effort. FWIW I am using the internal regulator, that I have modified to enable a remote start/stop of the alternator. I do not want the extra features and complexity (and cost) of external regs.


@Bycrick, you're right but there is not much I can do to lower the losses on the negtive side. It is a 70mm², I will not go bigger nor add another one. Connections & bus bar etc are super clean and oversized for 200A.



@rgleason, looking at page 3 of http://www.balmar.net/wp-content/upl...S-MC-614-H.pdf it seems there is only a positive Vsense to the battery and the rest is connected to the alternator. MS proposition to connect the MC614 direct to the battery makes sense. But it would mean a lot of cables for me (two engines about 6 meters away from the battery)


I guess the question in the end is whether my super idea of modifying the internal reg sucks because delco does not provide a true voltage sense anyway and I am stuck with a rather average charging profile, or if I am missing something ...
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Old 11-01-2020, 09:23   #7
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Re: Alternator voltage sense

Sorry for the TLDR post, hope you find it useful.

There are two options that I am aware of for internally regulated alternators with a separate voltage sense.

1. The elegant, but expensive option is the Nordkyn Design VR-200. You feed the voltage sense to the VR and then it “lies” to the voltage sense line of the alternator to get it to do what you want it to do. Essentially it is an external regulator that uses the voltage sense wire to control the internal regulator rather than controlling the field directly as do most other external units. Very nice unit with adjustable charge profiles, current limiting (with additional shunt), etc.$$$

2. You can install a voltage divider circuit in the sense line. This will add a fixed voltage drop to the sense line, how much depends on the resistor values you use. It will also add a few mA continuous load to the battery unless you have a switch to turn off the sense circuit. Design depends on how much current the voltage sense requires (should be very, very small). For example a 100Ohm-2700Ohm voltage divider will have a 5mA current at 14V and will have a voltage of 13.5V at the junction of the two resistors. The actual voltage will depend on the additional current required on the sense line. There is no compensation in this approach, but I have (do) use it on an internally regulated unit that is set for 13.8V. Very cheap.

You could also run a big negative cable from the engine block (where your battery negative is terminated) to the alternator case. This can help get rid of a fair amount of the negative losses as all the alternator negative flows through the mounting bolts and arms, to the engine block, through the block, and finally to your battery cable termination where it can get to copper. If you can safely do so, when the alternator is at high output measure the voltage from the case to the engine block “ground” terminal. If you get 0.1 to 0.2V you can get rid of most of that by installing a jumper from the block to the case. Make sure it is properly sized to carry full output current.
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Old 11-01-2020, 11:49   #8
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Re: Alternator voltage sense

Quote:
Originally Posted by Dsanduril;30537141. The elegant, but expensive option is the [URL="http://nordkyndesign.com/product/nordkyn-electronics-vrc-200-charge-reference-controller/"
Nordkyn Design VR-200[/URL]. You feed the voltage sense to the VR and then it “lies” to the voltage sense line of the alternator to get it to do what you want it to do. Essentially it is an external regulator that uses the voltage sense wire to control the internal regulator rather than controlling the field directly as do most other external units. Very nice unit with adjustable charge profiles, current limiting (with additional shunt), etc.$$$
very nice unit indeed, new to me, thanks for sharing. but doesn"t it sound crazy to buy such a unit, costing more than the 200A alternator itself, just because the alt is missing a proper negative sense wire ?

Quote:
2. You can install a voltage divider circuit in the sense line. This will add a fixed voltage drop to the sense line[...]
Yes but as I said the voltage drop varies (about .3V) depending on how much current the alt outputs. That means I would end up at too high a voltage when the battery is full.
Quote:
You could also run a big negative cable from the engine block (where your battery negative is terminated) to the alternator case[...]
The big black cable from the battery is already directly connected to the alt case, and from there to the engine block. However after recomputing the data, I should really not get such a high loss on the negative path. I think I will try to add a cable straight from the alt case to the battery neg (not going through the bus bar & shunt that is) see if the alt manages to reach the advertized 14.5V.
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Old 11-01-2020, 20:09   #9
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Re: Alternator voltage sense

Sorry, I guess Spot was right, Rom's is internally regulated.

Rom wrote:

"FWIW I am using the internal regulator, that I have modified to enable a remote start/stop of the alternator."

Rom I wonder what would happen if you bypass the remote disabling switch? That could be the source of your drop?

Too bad you couldn't put something like an adjustable rheostat (adjusts resistance to change current) but for voltage, well I guess that is an adjustable voltage regulator! They make these really inexpensive chips, something like this LM217 but I have no no idea many amps are needed in the alternator coil. Maybe someone who knows more could suggest one.

I have a question for you about the SI28 since you know the alternator. I am considering trying to install one on our Yanmar 3ym30 with a serpentine belt, but from some drawings of the alternator, it appears that the way I am mounting it the back end will be just 1/2" from the exchanger. Because I can swing the alternator out away a little, the exchanger will be in the way for less than 1/4" of the area of the back of the alternator. I have a drawing here.
Do you think I need to move the SI28 further forward somehow, to make more room at the back?
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Old 11-01-2020, 20:17   #10
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Re: Alternator voltage sense

Here is an adjustable voltage regulator for bosch alternators for $50, but it might not work on the SI28... They do exist though.
https://www.240turbo.com/AdjustableVoltage.html
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Old 11-01-2020, 20:43   #11
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Re: Alternator voltage sense

Sorry - I run a Delco 28Si but have modified it for external regulation. With the internal regulator even with the external voltage sense you run into various elements that drop the "realized" voltage.

The first that you identified is the voltage drop over the negative feed. Plus there is the temperature compensation to name the 2 big ones that I can think of.

Also, the actual voltage measured at the battery will greatly depend on the SOC of the battery. A 0%SOC battery will measure no where near the voltage set point and that may be "confusing" the issue.

Moving to external regulation was a great move for me. I was able to set the CC current that I wanted to de-rate the Alternator to 120 Amps from the sticker 200 amps as an example of the control that you can get.

Regards!
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Old 11-01-2020, 21:03   #12
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Re: Alternator voltage sense

An LM317 with a rheostat will adjust voltage down, but it will never go higher than the battery voltage, so that won't boost voltage to 14.5v like you want. Ebay sells them



There is a way to add two diodes with a switch to increase alternator output. That is diagrammed here nicely and explained by Smartgauge


SmartGauge Electronics - Increasing alternator charge voltages


See also http://www.soundsolutionsaudio.com/f...om-alternator/
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Old 11-01-2020, 21:15   #13
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Re: Alternator voltage sense

I wonder if the right Buck DC to DC converter would work?
https://www.ebay.com/sch/i.html?_nkw...&ul_noapp=true


They are not very expensive.
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Old 11-01-2020, 22:25   #14
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Re: Alternator voltage sense

Why do you have switches and fuses in the ground wire? Run a 2/0 wire from engine block to batt. Drop should be minimal.
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Old 11-01-2020, 23:37   #15
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Re: Alternator voltage sense

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Originally Posted by smac999 View Post
Why do you have switches and fuses in the ground wire? Run a 2/0 wire from engine block to batt. Drop should be minimal.

Congrats you read my first post carefully ;-) of course I made a typo, I meant "though the POSITIVE side usually accounts for a big half of the losses ..."


@rgleason, I have a custom made belt tensioner (and longer belt!) that allows me to set the 28SI further away from the engine. Not sure what you can do on yours but maybe you should just use and trust the internal regulator. Once again I don't want to use external VR or tricks, if possible, the internal regulator does a great job, except for voltage sense that is...


@evm, thanks but there again I do not see how downrating a heavy duty alternator from 200A to 120A with a 300 EUR external regulator is a great move.



So, I will try to rephrase the question: is delco (half) stupid to provide a single wire for voltage sensing where they really should have provided a positive & negative pair for that purpose, like victron does. Or is it accepted as good enough because "drop should be minimal" as smac says.
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