# 12v Regen System



## RIPPERTON (Jan 26, 2010)

Better than a DCDC converter is a system whereby a standard 12v alternator is belted to the main electric motor shaft and wired to the 12v battery via a relay that only closes when you are braking.
So basically a big relay that is triggered by the brake light circuit will connect the alternator to the 12v battery and apply load according to whatever current rating that alternator has.
This will appeal greatly to those with DC brushed motors.
I will be experimenting with this system on my Mira like it really needs more regen !!!! . but I would like some engineering input from others here to advise what kind of relay would be needed to close a circuit that will have current flowing in it. Kilovac Mosfet IGBT ??


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## Karter2 (Nov 17, 2011)

Presumably you will retain some form of voltage / charge regulator to prevent overcharge of the battery.
Lead or LifePo4 12 volt battery ?
What is the max continuous load on the 12v systems ?
What is the likely charge/discharge cycle rate likely to be on an EV with this system without a continuous alternator output to support the battery ?
Is the battery likely to see much deeper frequent discharge cycles which would affect its life ?


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## major (Apr 4, 2008)

RIPPERTON said:


> Better than a DCDC converter is a system whereby a standard 12v alternator is belted to the main electric motor shaft and wired to the 12v battery via a relay that only closes when you are braking.
> So basically a big relay that is triggered by the brake light circuit will connect the alternator to the 12v battery and apply load according to whatever current rating that alternator has.
> This will appeal greatly to those with DC brushed motors.
> I will be experimenting with this system on my Mira like it really needs more regen !!!! . but I would like some engineering input from others here to advise what kind of relay would be needed to close a circuit that will have current flowing in it. Kilovac Mosfet IGBT ??


Do not use a switch on the armature circuit. Just control the field of the alternator. Zero field current will mean zero armature current and a freewheeling alternator.


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## cpct (May 31, 2012)

The amount of energy that you will be able to recover with a tiny car alternator is negligable. It really needs to 'deliver' braking torque, which a small alternator can't.

For a large, higher voltage, motor, the amount of power that can be allowed to 'flow' back into the battery during braking is already a limiting factor.


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## RIPPERTON (Jan 26, 2010)

cpct said:


> It really needs to 'deliver' braking torque.


Not really. The scale of the 12v system is too small to be an effective brake but we can still harness such a system to do the job of a DCDC converter for increased range.
My 12v battery for example is a 4s3p 8Ah LifeTech that can handle 50A charge.
So 13.6v x 50A = 680w. 
We need up to 13kW to slow a car down.
The bottom line is an alternator regen system would be cheaper and more reliable than a DCDC converter.
You normally would keep the same alternator the car came with.
If you could buy a unit that varied the field as Major suggested.
So Major, how do you control the field in an alternator ?


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## rmay635703 (Oct 23, 2008)

RIPPERTON said:


> N
> So Major, how do you control the field in an alternator ?


Some alternators are 4 wire with 
2 being for current and 
2 being for sensing voltage

I have a 180amp alternator, if the 12v system can withstand 15v for a short period (FLA) you could maybe get around that amount out during a braking event.

3.8hp is nothing to sneeze at and would slow you down gradually.

If used in a real world system you would probably want a 210ahr 12v deepcycle array of some type, AGM being better for regen and lithium $$$ being best.

Cheers
Ryan


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## RIPPERTON (Jan 26, 2010)

We cant really expect to get real braking power out of such a system because 90% of the time the battery will be at 13+v and the alternator wont ever put out its maximum current when the battery is almost fully charged.
So still the only reason we would engineer such a system is because its cheaper and more reliable than a DCDC.
Even the energy that we will be harvesting is so little that we could even design 1 more cell into the main pack to cover 12v usage through the DCDC.
Plus to get braking effect from a 12v regen system you would need such a massive 12v battery and 2 or 3 160A alterntors that it gets counter productive


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## Tesseract (Sep 27, 2008)

RIPPERTON said:


> Not really. The scale of the 12v system is too small to be an effective brake but we can still harness such a system to do the job of a DCDC converter for increased range.


Using an alternator driven by the main traction motor to keep the 12V battery charged is a valid - and arguably more reliable - way of keeping the 12V battery charged compared to a dc/dc converter, but you are unlikely to see any meaningful increase in range. For one thing, alternators are very limited in power capability - 1kW max is common - so very little energy can be potentially recovered with one. Secondly, most people don't spend a large percentage of the time braking, thus the opportunity to collect energy will be limited. Thirdly, alternators almost always use claw-pole rotors which have an average efficiency of around 55%, further reducing the benefit to increasing vehicle range.

Don't get me wrong - if your motor has a tailshaft and you already want to drive the OEM power steering pump and/or A/C compressor then adding the alternator is, to me, a no-brainer, just don't expect it to miraculous increase your range, even if the field is only energized while braking (a la major's suggestion).



RIPPERTON said:


> My 12v battery for example is a 4s3p 8Ah LifeTech that can handle 50A charge.
> So 13.6v x 50A = 680w.
> We need up to 13kW to slow a car down.


'We need up to 13kW to slow a car down"?! The OEM brakes on most cars are capable of delivering 200kW+ of braking power; and many high performance sports cars have brakes capable of 1MW. The 1kW or so of an OEM alternator is but a fraction of necessary braking power unless you have the luxury of nearly coasting to a stop.



RIPPERTON said:


> The bottom line is an alternator regen system would be cheaper and more reliable than a DCDC converter.


No argument from me on both counts - alternators are generally more reliable and definitely cheaper if your motor has a tailshaft (mainly because you already have the OEM alternator from the car you are converting).



RIPPERTON said:


> So Major, how do you control the field in an alternator ?


On most (all?) modern alternators the field current is controlled by an internal "regulator module"; it will require quite a bit of hacking to access the field terminals to do as major suggested. Older alternators (mid 80's and earlier) had a separate field terminal and an external regulator so they would be much easier to adapt in the fashion you've proposed.


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## RIPPERTON (Jan 26, 2010)

ooh the gears are turning down here
it gets better
regen alternator WITH vacuum pump 
running off an Aircon compressor clutch that only engages when the throttle is off.

http://www.ebay.com.au/itm/NEW-MITS...=AU_Car_Parts_Accessories&hash=item2a34384e6d


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## Roy Von Rogers (Mar 21, 2009)

Just connect the alternator up, like in an ice vehicle. The regulator will keep the battery charged while driving, no different then a dc/dc would.

When the battery is full, the regulator will turn off, but since your always using 12v while driving, it will keep the battery up just like a dc/dc.

If your going to hook up a relay to the brake, use it to turn the field winding off, so when your sitting in traffic, your not energizing the field windings.


Roy


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## Karter2 (Nov 17, 2011)

Roy,
no point in using the alternator full time, thats just churning electrons and wasting energy. (using the main pack & drive to run the alternator)
You only want the alternator to charge during deceleration, so that is using kinetic energy not main pack energy,
Sure, you need controls to de-energise it when stationary too .
But unless you are careful, you may either drain your 12 volt battery on a long highway run or have to use a big 12 volt pack and a juicy (200A) alternator.
I guess you could always have auto charge control that energized the alternator if the 12v system dropped below a minimum level ?


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## bwjunkie (Jul 31, 2013)

Karter2 said:


> But unless you are careful, you may either drain your 12 volt battery on a long highway run ...


how is that possible? If an EV drives for 1 hour solid on the highway, you'd have to be drawing 50+ amps off your 12v system to drain a typical smaller battery? or am I doing some wrong math? 

My thoughts on this topic are to have a DC-DC that you only turn on when you are on shorter trips or parked and charging, or when your 12v gets low for whatever reason, because I admit it does seem to happen occasionally. 

josh


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## Karter2 (Nov 17, 2011)

Remember , a 50Ahr lead battery won't give you 50 amps for an hour.
Even at 25 amps drain you would be lucky to get an hour out of it .


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## Duncan (Dec 8, 2008)

Karter2 said:


> Remember , a 50Ahr lead battery won't give you 50 amps for an hour.
> Even at 25 amps drain you would be lucky to get an hour out of it .


It's actually worse than that - you might get your hour - but the battery would then be knackerred!

With a normal car battery you should never draw more than 10% - or it will quickly die


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## RIPPERTON (Jan 26, 2010)

bwjunkie said:


> My thoughts on this topic are to have a DC-DC that you only turn on when you are on shorter trips or parked and charging, or when your 12v gets low for whatever reason, because I admit it does seem to happen occasionally.


This is the next best solution and by far the easiest to engineer but you would need to switch and put a precharge resistor on the high side.
Having a DCDC running all the time is unnecessary.


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## Frank (Dec 6, 2008)

You could also fit a second alternator with big-ass resistor and make heat...


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## RIPPERTON (Jan 26, 2010)

$66 worth of Pregia diesel alternator and another $66 worth of Astra AC compressor should keep me busy for a couple of days.
Im going to cut out the mounting boss off the compressor and fit it to the front of the alt so its easy to refit the electric clutch. 
I have to remove the splined section from the pressure plate of the clutch and make something that will better fit the alt shaft.


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## RIPPERTON (Jan 26, 2010)

Clutch mounting stub is cut off the compressor housing and screwed to the front of the alternator housing with 12 M4 screws. Only problem is it doesn't quite fit in the Mira so does anyone want to buy it ? $200 AUD



done but the clutch draws 3A and it really should be on the motor so the belt doesn't turn all the time.


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## jk1981 (Nov 12, 2010)

Can't you just control the alternator field current so you're not switching high charging currents in a highly inductive circuit? Doing that your switching requirements would be quite modest (you'd have to check your particular alternator for exact figures).

The problem I see is unreliable braking load (varies with state of charge), abrupt load changes and possibly inadequate charging of the 12V system.

jk


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## major (Apr 4, 2008)

*Why a clutch?*



major said:


> Do not use a switch on the armature circuit. Just control the field of the alternator. Zero field current will mean zero armature current and a freewheeling alternator.


I don't understand the clutch at all. What sense does it make


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## RIPPERTON (Jan 26, 2010)

*Re: Why a clutch?*



major said:


> I don't understand the clutch at all. What sense does it make


The clutch is engaged only when the throttle is off so you get kinetic regeneration of the 12v system but the real logic is you get brake booster vacuum at the same time so you don't need an electric vacuum pump saving more energy. You probably would still use a one way valve and a vacuum tank to get the 4 assisted applications after stopping.
This unit would only make about 1kW of braking energy so it wouldn't slow the car down very much but it would be just like an engine brake in a petrol car.
Were just trying to get around the problem of DCDC converters being either insanely expensive or unreliable.


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