Dual Battery Question
Posting Guru
Joined: Jul 2005
Posts: 1,006
Likes: 0
From: San Jose, CA
The two batteries in our trucks are directly wired in parallel so they can pump out current equal to the sum of both batteries.
In theory, if each one is rated at 600CCA, you get 1200CCA combined
Why 2 on diesels? They've got to supply enough juice to keep the 8 glow plugs running long enough to heat up and then still have enough juice left over to crank the engine at the same time.
If a typical glow plug draws 150W, that works out to about 12-15A each. Multiply by 8 cylinders equals over 100amps of current that's got to flow while the engine cranks. A single battery probably won't last very long trying to turn over a frozen engine.
Dual alternators are also wired in parallel. The output capacity is the sum of the two. It's probably more efficient to have 2 do the work of 1 huge alternator of equal capacity. There's also the economy of scale... Ford only needs to spec one standard alternator and use more of them instead of spec'ing two
different units
I seem to see some camper setups using isolators among several batteries...that's done to share the alternator and prevents draining the main battery(ies) used to start the engine.
Side note--I think our factory batteries are 600-something CCA's. Technically speaking, if a single Optima battery can supply the same CCA's as the 2 factory batteries, we'd only need to buy one of them and shave 50lbs off the truck. Put two of those guys in and you can turn over a 747 jet engine.
In theory, if each one is rated at 600CCA, you get 1200CCA combined
Why 2 on diesels? They've got to supply enough juice to keep the 8 glow plugs running long enough to heat up and then still have enough juice left over to crank the engine at the same time.
If a typical glow plug draws 150W, that works out to about 12-15A each. Multiply by 8 cylinders equals over 100amps of current that's got to flow while the engine cranks. A single battery probably won't last very long trying to turn over a frozen engine.
Dual alternators are also wired in parallel. The output capacity is the sum of the two. It's probably more efficient to have 2 do the work of 1 huge alternator of equal capacity. There's also the economy of scale... Ford only needs to spec one standard alternator and use more of them instead of spec'ing two
different units
I seem to see some camper setups using isolators among several batteries...that's done to share the alternator and prevents draining the main battery(ies) used to start the engine.
Side note--I think our factory batteries are 600-something CCA's. Technically speaking, if a single Optima battery can supply the same CCA's as the 2 factory batteries, we'd only need to buy one of them and shave 50lbs off the truck. Put two of those guys in and you can turn over a 747 jet engine.
Tuned
Joined: Jun 2004
Posts: 338
Likes: 2
From: Northern MA
Spot on there but I do wonder about the optima batteries. As you mentioned the diesel needs a lot lf power, more than 100 amps just for the glow plugs, plus pumps etc. Then to spin a big engine at greater than 400 rpm.
Optima batteries seem to be rated at 800 CCA from what I can find, I'd be interested to see how they do on a frozen engine.
Optima batteries seem to be rated at 800 CCA from what I can find, I'd be interested to see how they do on a frozen engine.
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