Fuel Economy, Hypermiling, EcoModding News and Forum - EcoModder.com - View Single Post - Test: Alternator vs. no alternator = 10% MPG gain @ 70 km/h

Crashy · 05-19-2018, 06:06 PM

I have managed to read the whole thread and would like to clear up some misconceptions. Then I will provide solutions to some of the issues raised.

1. Lead acid battery has a "safe dod of 50%"
False. The number of amp hours you can get from a lead battery is fixed. A cheap one will give around 5000. Average 10000. Really good one 20000. Let's use average 10000 as an example with 100Ah capacity. You can discharge 10ah 1000x, or 20ah 500x, or 50ah 200x, or 100ah 100x. In every instance the number of amp hours is 10,000. There is no magic line in the sand where one side is safe and the other side is risky. People seem to think that a 10% discharge and a 50% discharge will have the same effect on lifespan, but a 50% discharge is equal to 5 discharges of 10%

2. Alternator power is 5x more expensive than grid power
False. It is 20x more expensive depending on where you live and the car you drive

3. A smaller alternator is more efficient
False. Your loads are the same. If you undersize your alternator it will work hard, overheat and become very inefficient. If anything, you should oversize it for better fuel efficiency because it will run cooler

4. Deep cycle lead acid is a good suitable battery to use for this mod
False. It is terrible. The charge efficiency of a lead acid battery is 45% between 80 and 100% state of charge. Below 80% soc it is 90% efficient so if you must use lead batteries the ideal range is 60-80% but this may result in sulphation. The added weight of the batteries and poor input / output efficiency will cancel out any fuel savings. Unless they are grid charged

5. Supercapacitors are a good addition
False. They have high self discharge and adding losses to a system cannot possibly improve efficiency

6. Alternators don't waste much horsepower when unplugged
False. Bearing, belt and fan friction are still present and are significant. Self excitement of the rotor is still occurring unless you disconnect the main and rotor wires. Try spinning a removed alternator by hand for 2 minutes. Your arm will ache

05-19-2018, 06:06 PM	#369 (permalink)
Crashy EcoModding Lurker Join Date: May 2018 Location: New Zealand Posts: 30 Thanks: 14 Thanked 1 Time in 1 Post	Myths debunked I have managed to read the whole thread and would like to clear up some misconceptions. Then I will provide solutions to some of the issues raised. 1. Lead acid battery has a "safe dod of 50%" False. The number of amp hours you can get from a lead battery is fixed. A cheap one will give around 5000. Average 10000. Really good one 20000. Let's use average 10000 as an example with 100Ah capacity. You can discharge 10ah 1000x, or 20ah 500x, or 50ah 200x, or 100ah 100x. In every instance the number of amp hours is 10,000. There is no magic line in the sand where one side is safe and the other side is risky. People seem to think that a 10% discharge and a 50% discharge will have the same effect on lifespan, but a 50% discharge is equal to 5 discharges of 10% 2. Alternator power is 5x more expensive than grid power False. It is 20x more expensive depending on where you live and the car you drive 3. A smaller alternator is more efficient False. Your loads are the same. If you undersize your alternator it will work hard, overheat and become very inefficient. If anything, you should oversize it for better fuel efficiency because it will run cooler 4. Deep cycle lead acid is a good suitable battery to use for this mod False. It is terrible. The charge efficiency of a lead acid battery is 45% between 80 and 100% state of charge. Below 80% soc it is 90% efficient so if you must use lead batteries the ideal range is 60-80% but this may result in sulphation. The added weight of the batteries and poor input / output efficiency will cancel out any fuel savings. Unless they are grid charged 5. Supercapacitors are a good addition False. They have high self discharge and adding losses to a system cannot possibly improve efficiency 6. Alternators don't waste much horsepower when unplugged False. Bearing, belt and fan friction are still present and are significant. Self excitement of the rotor is still occurring unless you disconnect the main and rotor wires. Try spinning a removed alternator by hand for 2 minutes. Your arm will ache