Do-it-yourself regenerative braking?

[zman]

So all the problems with energy storage after it is recovere by spinning the alternator got me thinking about producing hydrogen.

Istead of using H in a fuel cell I was thinking about introducing it to the fuel-airmixture by piping it to the intake manifold.

The alternator would spin when in regen brakeing mode and generate hydrogen. The selenoid operated valve would be shut to keep H out of the air manifold. When the light turns green open the valve and allow it to mix in with the fuel-air mixture for power.

All of this is done in low pressure enviroment so no danger of explosions.

I don't know how much energy would be recovered, but it would be relatively easy to set-up.

[Daox]

While that might be viable and would in fact work, the inefficiencies of all the energy conversions add up like crazy. First, you convert your motion to electricity, then electricity to hydrogen, then hydrogen to physical motion again. By the time you do all that, you only have a tiny fraction of the original energy you were trying to capture.

[zman]

I totally agree, the inefficiencies are huge, but the objective is to recover some energy in the easiest way possible otherwise we are releasing brake dust and heat into the atmosphere. This system would acomplish two things, slow you down without the use of brakes and give you little boost while taking off.

[Daox]

Quite true zman. Give it a shot and see what you can get out of it.

[Tesla]

I was doing a bit of digging on alternator mods and just thought I might add to this old thread.

I like some of the ideas, but there is always the complexity vs net gains issue.

I think there is merit in doing a type of "smart" alternator control to gain some regen advantages, but knowing the gains are going to be small means the system needs to be simple.

So we need to trick the alternators behaviour to suit our driving needs, I still need to get a better idea of how mine works, but from reading around it appears the sense/sensor wire is to report system voltage back to the regulator, it used to be connected to a high load point so where voltage is lower, but this would often cause engine to bog down or surge when fans etc were turned on and off, in most vehicles these days it will likely come from the ECU to allow a "soft" start so engine can adjust as alternator ramps up.

So if we can manipulate the voltage in the sense wire we can get the alternator to either ramp up or scale down, the only thing I'm not sure of is whether it is a straight voltage or a pwm signal.
In some it definately is just a straight voltage as I read about some hot rodders doing a boost mod where they intercepted the wire and put a 9v supply on it which kicked alternator in and gave a system voltage over 15V, gave them more power through the injectors etc., only for temp use though probably no good for the battery, anyway this got me thinking about how alternator works.

It's not just enough to ramp the voltage up, as I understand it, the alternator tries to maintain a set system voltage, the actual power generated will be governed by system load, so if your battery voltage is higher, well charged, when you try to regen brake, there won't really be much effect, but if your battery is nearly flat, then alternator current will be high and load will be much greater, so it's not enough to just switch alternator in and out, we need to also manipulate alternator load to get the best effect.

One way to manipulate load may be to run two batteries, one dedicated to engine and vehicle systems which is always kept fully charged and the other half charged and simply having a large solenoid to switch in the low battery when regen is required, it's low state of charge would pull the system voltage down and also provide a high load to draw current from the alternator, ideally some form of "soft" switching that can fully swap from high to low battery, but there is a case of how best to manage system to ensure batteries are not damaged and small gains lost in cost of batteries.

So I am trying to think of electrical loads that can be applied during regen to maximise alternator loading, but not just needless loading it needs to be things that would normally be required during the course of a trip or could be stored on a temporary basis and be used to aid acceleration etc.

[serialk11r]

That hydrogen idea is actually pretty clever and new (to me at least), but I guess the question is how much hydrogen can you actually generate? It's probably not much considering the poor conversion efficiency of electrolysis, but still it's cool to think that maybe 10% of the braking energy can be turned into fuel through an alternator bypass and water tank, pretty neat!

I think the main thing holding back having the alternator do meaningful regeneration is the fact that they are regulated to 14V, which is really low. At 50V you'd be able to pump 3.5 times as much electricity, and your engine only needs to be at maybe 2300rpm to do that. If the ratio of alternator drag to engine braking is high enough the alternator could be a very effective regenerative brake. They're talking about changing the 12V electrical standard, but that might not be necessary if start stop/mild hybrid systems with their own high voltage circuits become more commonplace.