Alternator delete with lithium and lead acid battery
 

Brucepick has been working on an interesting alternator delete for a while now. He wanted to eliminate the load on the alternator, but didn’t like the idea of just replacing the starting battery with a deep cycle lead acid battery. The downside of doing this is that as the battery discharges the voltage sags lower [...]

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I had similar thoughts recently when I realized that, with a certain amount of effort, I could get my summer average to 40 MPG.

My idea is a two position alternator switch. Position 1 would be "normal". Position 2 would shut off the alternator. The truck would continue to run off the standard battery. A second deep cycle battery would charge the standard battery through a DC-DC converter with about 14 volt output. The second battery would be charged from a flexible solar panel mounted on my topper and charge controller. I would want the deep cycle battery to be sized for four hours at 20 amps into the standard battery. The solar panel should fully recharge the deep cycle battery in 8 to 12 hours.

I don't think I'll ever do it, but it's a great thought experiment.

So if I want to just drop in a deep cycle battery and remove the drive belt on my Metro, what's a reasonable guess for my safe range (miles per amp hour)before recharging? I'm guessing cranking power isn't an issue. Yes, I know there are some imponderables, I'm looking for a ballpark number. Also, what reasonably priced, readily available batteries have a decent amp-hour/pound ratio?

Most guys just replace their normal starting battery with a lead acid deep cycle battery. My group 24 (probably ~70Ah) battery in my Paseo would easily get me back and forth to work a little over 40 miles when I had that commute. It was fine even with my fan blasting in summer, and wipers/headlights going in rain.

I had the exact same idea recently, except that the charged auxiliary battery would also run a couple of small self-adhesive heater pads for engine sump and gearbox - to reduce warm-up times in winter, or in summer come to that.

I'm planning to start with the aux battery and variable input dc/dc converter to see how it works, then add a mains charger for the aux battery. If mpg gains are appreciable I will invest in a roof-mounted solar panel and charge regulator for the aux battery. I'm hoping that simply supplying a slightly higher voltage to the car's normal system (14.8v?) the alternator will 'decide' not to bother putting any amps out, and I will therefore not need an alternator kill switch.

But did you ever make the thing?

I might admit I'd be quite afraid to delete the alternator into any vehicle, unless it was either an old-school Diesel or some air-cooled Volkswagen (in such case I could still use a stator from some 4-cylinder motorcycle with distributorless ignition). Some other energy-saving measures such as all-around LED lighting might be also considered to decrease the electric load...

Ebay has, for $90, 30amp, 36v to 12v DC to DC converters, you would still want a $25 ridding lawn mower starting battery to turn the starter over, but 3 cheap deep cycle batteries would give you alternator-less driving for 100's of miles without dimmed lights.

Get a DC-DC converter for 13.8 volts and put in an alternator ON/OFF switch. Lead acid batteries like about 14.3 volts (varies slightly depending on temperature) to be fully charged, and about 13.8 volts for a sustain charge. Too much voltage is bad for the battery, it converts the water into hydrogen gas.

Turn the alternator on about once per week just to make sure it still works and to top off the battery.

It takes almost a full kilowatthour of power to put enough heat into an engine to do any good. That's enough to drain a good sized deep cycle battery.

Sounds good. Do you have any details of the dc/dc converters?

I was thinking of using a couple of 150w car laptop adapters from Maplins set to 15v regulated output. A similar price to achieve a similar output. (Well, 250 watts seems about right to cover the load during normal running conditions.) Laptop adapters tend to be fairly efficient these days. They take a nominal 12 volt input but I have been told they will accept anything between about 11 volts and 15 volts input. In other words, they are designed to run on lead acid batteries, even significantly discharged ones. Using two such adapters in parallel should work fine I think, especially if they are feeding a system which has a big capacitor attached, in the form of the regular starter battery.

My hope is that by feeding in a sufficient current at a voltage just above the voltage at which the alternator regulates its output (14.4v?) the alternator will be 'fooled' into 'thinking' that the car's electrical load is zero watts and will therefore spin easily around without putting any power into the car. (15 volts is probably just about right, and happens to be a common laptop PSU voltage.) When peaks of current are demanded, the dc/dc converters (laptop adapters) will not be able to provide that much current, so the peak current will be provided by the starter battery, voltage will drop below 14.4v, and the alternator will respond by kicking out amps as normal, ...but for most of the time the alternator will be idle.

Someone, please, correct me if I'm wrong here but I think this would mean that no switches or alterations would be necessary at all, beyond feeding that regulated 15v output into the car's electrical system at some suitable point. When the auxiliary battery becomes exhausted and its voltage drops, the adapaters will no longer be able to maintain the 15v and the aux battery should stop discharging. The alternator will then take over.

Ideally the battery should be about 250Ah. Perhaps 2x 6v 250Ah batteries in series, so each battery can be moved around without lifting gear! But I'll start with one cheap 12v 65Ah leisure battery to test the concept. That will be light enough to carry indoors every evening to put on charge overnight.

15 volts is slightly higher than the normal voltage in my car but should not cause a problem, either for the battery, or the ECU, or for any other component in the car. Indeed, some alternators will output 15 volts anyway. 15.5v might be too high but 15 volts should be no problem.

Someone correct me if my logic is wrong here! What have I missed?

Hmm... Thanks JRMichler. That would work. And yes, I was thinking of 2x 50w pad heaters on both gearbox and engine sump, left switched on overnight. That does add up to about 1Kwhr. Yes, probably not a suitable use for a battery. But leaving the car 'plugged in' overnight could charge the aux battery and warm the engine.

Probably best then to use mains voltage pad heaters reather than 12v ones. It would be nice if a large solar panel could provide enough charge in the battery for the pad heaters but that's probably too much to expect, and in any case that would mean the battery is exhausted by morning, which is the opposite of what you want. But a plug-in overnight thing would work. Even in (the cool, British) summer there should be some gains from starting the day with a warmer engine and gearbox.

I like this idea. Main flaw I see is that your input voltage will have to be tightly regulated to avoid dumping a lot of charge current into the starting battery. The dc-dc converters I have used in my EV conversion swing pretty wildly according to load, and that's even with a 12V AGM battery for buffer. Even so, if the dc-dc is set for say, 14.5V, it won't pass many amps into the starting battery, and the alternator should kick in to level off the voltage any time you exceed the dc/dc capacity. Measurement of the energy removed from your supplemental battery will be much more precise and immediate than discerning the MPG effect.
I had hoped that simply replacing the SLI battery with Lithium Iron Phosphate would do, given the higher resting voltage of four lithium cells, but that would require detuning the alternator to not kick in until approx 13.8V or less.

Searching for such a product lead to several interesting sites, but mainly products designed to increase alternator load rather than the opposite. Here's one that might be fooled into doing what we want...

Advanced Alternator Regulator

Interesting. I hadn't come across these 'advanced' alternator regulators. Intelligent, multistage charging in cars seems a good idea.

(Car manufacturers are very conservative when it comes to changing tried-and-tested systems. One consequence of that conservatism is the vastly increased reliability of most modern cars compared to older cars, but another consequence is that cars still use very out-dated technology. One example I'm struggling with right now is the blower motor speed control mechanism. My car uses an array of resistors to slow down the motor, totally wasting about 50w of energy at all speeds except the maximum speed. I've just bought a Pulse Width Modulator speed controller which should save me at least 40 of those 50w and gain me one or two mpg in the process.)

But have you seen these...?

http://www.youtube.com/watch?v=GPJao1xLe7w

Using a capacitor array instead of a massive lead acid battery for starting would mean there is absolutely no problem with running a slightly higher voltage as there's no battery to overcharge. Your DC/DC converter could be set at 15v, effectively disabling the alternator. When the auxilliary battery is no long able (or no longer allowed) to power the DC/DC converter, the voltage will drop and the alternator will kick in and take over automatically. No change to the basic electrical system necessary: just plug in the auxilliary battery and DC/DC converter to a cigarette lighter socket or similar and away you go. Any brief current peaks will be easily handled by the capacitors so a steady 30A from the DC/DC converter should be adequate.

However, I've changed tack on my auxilliary battery idea and I'm going to go with a single, large AGM battery for the time being. I got the largest AGM battery I could cram into my existing, stock battery tray without cutting or extending anything. It's 90Ahr so not enormous, and it cost £90. Apparently AGM batteries are well suited to daily discharges of up to 50% as long as they are then recharged daily. The manufacturers claim this one will be good for 1000 50% discharge cycles and it comes with a 4 year warranty.

The reason I changed my mind and decided to see how I get on with just one battery is that I measured my car's actual current draw under a variety of conditions (various different equipment switched on) and was pleasantly surprised at how little current it takes just to run the engine. Other equipment, like the blower motor and windscreen wipers, used more than I expected, but for the ignition (well, it's a diesel) the CPU and the engine - the minimum necessary to drive the car in daylight - I only need 6.4A. I reckon I can mostly get away with using less than 20A, so that's a good 2 hour range on a 90Ahr battery without going below 50% SOC. For long journies I'm going to need the alternator anyway, and since there is no point running the battery down just to run it back up again with the alternator on the second half of a long run, the savings can only really be made on shorter trips. (Did that sentence make sense? It's been a long day!) But, the vast majority of my car use is for daily short journies from home, and is generally well under two hours, so I think I should get away with a single battery. At least I'm going to try that first. The 10A waterproof, temperature compensated, all singing automatic AGM battery charger arrived today and I'm testing it out before installing it in the car.

[Edit: With a second, auxilliary battery of course on long journies the same saving is possible as with shourter journies since the auxilliary batery can be used to save all the alternator induced fuel use up to the point where it becomes depleted. Still, most of my journies are short so that's where most of my fuel savings are to be found.]

I managed to identify and disconnect the field wire to the alternator (the 'ignition wire' that goes from the dashboard battery warning light) and that successfully prevents the alternator from starting up. An alternator ON/OFF switch on the dash will be easy to implement.

So my attention is turning at the moment to making the car electrical system less wasteful so as to maximise my alternator-free range and maximise mpg on longer trips. Hence looking at the blower speed controller. At the lowest speed the blower uses 25w but WASTES 50w in the resistor! At Speed 2/4, which I most often use, the blower uses 53w and the resistor wastes 53w. In winter especially I can't drive without the blower motor on and it makes me sick to think I'm wasting all those amps through those prehistoric resistors.

I also replaced all the light bulbs I could with LED's and got more efficient, low energy headlight bulbs. The lighting upgrades save me 52w in total when I'm using headlights, which is definitely worthwhile despite the cost of all the LED's and all the hassle of sourcing and fitting them, but the blower motor is on ALL the time and is wasting about the same amount (53w). The PWM to replace the resistor array is costing just £10.

(These wattages are at 12.4v without the alternator charging. At 14.4v they're all increased by 30%)

Doh- I have an ultracap pack on my 6.9l diesel truck as a starting booster and love it, intend to try it on the EV, but didn't put the two together for this idea!

What spec's (Farads, volts?) are those Maxwell capacitors?

Ultracap bank with higher V reserve battery
 

My ultracap bank is seven 2600 Farad Maxwells, put together with a balancer by EBay seller cusdn, had it 3 years now. Here's a current listing for an identical version.

Maxwell BCAP0010 7 Ultracapacitor Surge Booster Assembly | eBay

I put it inside a plastic box with an Anderson connector, so can easily swap it from vehicle-to-vehicle. It can crank the 6.9L International IDI diesel all by itself, but sure puts a load on the alternator right away, since ultracaps want those electrons back just as fast as they'll give 'em up!
I've yet to try it for a long drive in the EV conversion, but intend to.

Hadn't put two-and-two together yet for using it as part of an alternator shutoff/delete. Running off the ultracap only provides such a small buffer that it would pert' near immediately transfer all load to the alternator, but switching in a lithium house battery that can maintain 15V under load sounds like a great way to unload the alternator. Thanks!