How do you size Alternator?

[GEOO]

I have a 78 amp hr Battery. Group 27 type.
How will my voltage change when I opperate the trim tabs? My concern is lowering the voltage to the fuel pump.

Electrical Items:
Fuel injection. 18 amps
Fuel pump. 15
MSD ignition 10
Water Injection pump. 12
GPS, Depth Finder, etc. 2
Blower 4
Bilge Pump #1 4
Bilge Pump #2 7
Two Trim Tab Pumps. (Rocker Plates) 20-50 each
Arneson Drive Trim Pump. 20-50
Lights?

[mphatc]

GEOO,

Need a bit more info . .

For each of these items which ones are running 100% of the time, and what percetage of the time you are running are the others in use?

Obviously your largest constant draw is the ignition, fuel pumps and fuel injection, and if you do a lot of night time running you ought to factor that in.

Also consider if your alternator is underdriven!

MPHATC

[GEOO]

At WOT I draw 50-60amps constant. Then when I adjust the Rocker Plates or Drive, I draw an additional 50-100amps; the fuel pump may have a voltage drop at this time and may take a few more seconds for the pump to see full voltage (13.4?).

Do you size an alternator for the draw (amps) while running or by the battery size? Does it hurt the alternator if you spin it too fast?

[oldLenny]

Geoo, that seems awefully high. The current you are drawing. Have you put on a "clamp style" ammeter over the positive lead between the battery and the starter while running and set it to peak and hold to arrive at this value?

That is a lot of juice and I haven't seen any windshield wipers, headlights or boom box anywhere on your boat. :D

I would think if an alternator saw a 150A draw (requirement) from your motor it would unbolt itself and leave.

[MOP]

You can run at night it must glow in the dark, take Lenny's advice and check it with a clamp meter. Do you have an dash ammeter that shows that much draw?

[GEOO]

I'm just adding up the amp usage for each item. Most of the figures are from the manuals of the accessory. ?

[BUIZILLA]

GEOO, you obviously have some fabrication talent. With that being said, I would run 2 Motorola or equiv marine alternators, of about 65A each.

J

[MOP]

Jim has a good idea, I have done that on several boats over the years. You have to split the systems so all your critical stuff is isolated and the alternators don't buck each other, the grounds are the only thing that stays common. Use one for the ships power (starting and ram pumps and bilge pumps) and one for electronics with a good filter which may be a good idea for you. you will have the added weight of the extra battery and some wiring to separate the system but it should cover your bases.

[oldLenny]

WOW...just got off the phone to Arneson...

Semms the trim pump for the drive, and the trim pump (individual) for the rocker plates each have a MAXIMUM draw of 50A, require a 20 amp capable switch, so we can assume a momentary hit of 3 times this amount (20)for a few milliseconds and then it will level out. Geoo, the only way to cut this gigantic demand would to be go to a 24 volt system (available) and cut current requirements in half but that would sewer your electrics in the rest of the boat and create a nightmare in way of batteries and charging.

That is a LOT of current.

As Jim said, you might be looking at another alternator for this package or massive reserves available through the batteries in parallel.

Sounds like you will be adding another 10 pounds aft of CoG.

I would again run the boat, with clamp meter, and have it planing and adjust drive, raise rocker plates and see what is the value. Both peak and hold and a "balance" (continuous).

[GEOO]

Lenny,

Most of the electric trim pumps are the same,( Bravo's, Arneson's, K-Planes, Rocker Plates). They all draw a lot of power. My concern was at WOT when the fuel pump needs the voltage to build enough presure and the ignition needs to stay HOT. The few second's of tab operation could cause the voltage to drop creating a low fuel pressure problems? or not enough spark to light the plugs.
I found a few companies that make alternator's of 100-150amps with remote regulators. One company told me this would not help. That the battery has to absorb the power before the power can go out to the accessory and that he group 27 battery can only absorb 50-60 amps??

[BUIZILLA]

Hmmmm, we're dealing with an 18' craft... cramped quarters...

Look into (2) Group 27 Optima batteries if they can handle marine abuse, prolly 850-900 CCA each, Run ONE HD battery switch with 2 gauge cable feeding each side of the switch and 6 gauge feeding the toys. Parallel the sourcing. Then (2) 65A alternators, each feeding one battery. If you stack the alternators, you can use one 7/16 HD ribbed belt, and one pulley. I've seen this done before. I'm NOT a marine electrician, but a lot of careful thought can solve this dilemna. The saving grace in this, is the load factor is really only a surge, non-continuous load. The strong battery's can absorb the surge, the 2 alternators can maintain the battery's. My last Ford powerstroke had (2) Group 27 battery's and (2) alternators, so I know this can be done. A pair of Group 31 battery's in an 18 is an overkill. I know you can use a single 225A marine/truck alternator as well. I think Leece-Neville makes what you need.

J

[MOP]

George as long as you split the systems IE isolate one from the other your engine electronics will have all the juice they need. Run your pumps off a separate dedicated battery and alternator, two 65's should work the Leece-Neville will do the job but it is very heavy and takes HP to drive it. It may be possible to run larger say 100 amp with an isolator to the separate batteries and run just the heavy stuff of that battery save some weight and keep it simpler. One of my best Buds runs L&L one of the largest electric shops I will pick his brain tomorrow and get back to you.

Phil

[Tidbart]

Just my $.02 worth.
Don't over engineer this situation.
My first question, is this a problem? I am referring to the voltage drop to the fuel pump or are you just asking if it could become a problem? Have you been experiencing a problem?

You asked how the voltage will change when you operate your tabs....The answer is it will drop the voltage some. How much depends on a number of things like wire size, wire length, actual load, and diversity to name a few. This is to be expected. The voltage may not drop below a point where your fuel pump will stop working.
Generally, a battery at rest will read 12.6 volts, 2.1 volts per cell. An alternator will put out about 13.2 to 14.6 or higher depending on the regulator and if it is working. What I am saying is that the pump may work down to 12 or 11 volts and may not see the dip. Momentary bursts are far different than continuous load and a good system should recover from them.

Going back to the diversity that I mentioned earlier. What are the chance that you will be operating all of these pumps at the same time? Not very likely. So you can leave off some of the pumps for calculating load, this is the actual versus the connected load.

You also asked, "Do you size an alternator for the draw (amps) while running or by the battery size? Does it hurt the alternator if you spin it too fast?"

You would size an alternator by the actual load. By this I mean by the actual draw of the equipment you have on and working. This goes back to putting an ammeter on the alternator as was previously suggested. You have to look at what is being drawn by the equipment or you can add up the nameplate data of the equipment. Just because some thing is being fed by a 20 amp breaker, doesn't mean that is draws 20 amps.

As for spinning the alternator too fast, yes it can damage it. To slow down or speed up the alternator you can change the pulley size. By changing the pulley size you change the ratios. The ratios depend on the range of rpms you run. I know you boat is fast but I have no idea what rpm you run.

I guess my point is this, there is a bit of homework that needs to be done before a decision is made. 2 alternators, 2 batterys, switches, wires, brackets, fabrication, time, and money are all factors. If I could do it with one battery, one alternator and existing wiring, I would.

If I was to guess, you could get away with a larger, alternator (100-125 amps) and maybe an optima style battery(850 CCA and smaller than a 24 series battery. I don't think they make a 27 series size, they don't have to. I said, if I was to guess, I would still do my homework and not guess at all.

Sorry for the looooong post. This is not as simple as someone might think.

After all that I would say to drop Bryant (Donzi Blackhawk) and email. He should be doing this type of thing everyday.

Bob

[GEOO]

Thanks Guys,
I was getting different info from suppliers. I finally called Balmar and they sell an 110 amp alt. which seams like a good idea. They said to size the alt for the load of accessories with excess for charging the battery. I think my 55 or 65 amp alt. is at it's limits.

The fuel pump rating is at 13 or 14 volts if the voltage drops the pump might not flow enough. (add the possibllity of a dirty filter etc..)
At WOT I run the Ignition System, Fuel Injection, Fuel pump, Water Injection pump. Then momentary blower, bilge pump & trim pumps.

If I keep the battery fully charged the brief draw of the trim pump should be fine.

It's not something easy to test. If there is a problem with voltage then the engine goes lean it's not a good thing!!

[mphatc]

GEOO,

You might need to size your alternator for max engine speed if you are running that mouse over 5000 . . . .

This may very well mean that it is underdriven and does not charge at low speeds or at start up until you rev the engine to excite the electronics.

I set many of the BMW race cars up this way because we run at 7000-8000 rpm for extended periods. :D :D

MPHATC
hoping to run 75% of GEOO's speed . . frown

[Rootsy]

5K? heck i think i got whiplash watching geoo's tach in a few of those videos... eek!

[GEOO]

I was worried about the rpm's too. However, the guy I spoke to at Balmar said their 712-110 model is rated for 12000 rpm's and tested to 18,000. Even with a 2:1 pulley ratio I should be fine and have power at 750 rpm's. Thanks.

[BUIZILLA]

I routinely run my factory 63A Delco alternator in Mighty Mouse to 7400, been as high as 8400, no problems yet. :D

J

[MOP]

You can't go wrong with the Balmars they are the one of the very best alternators, I was on the wrenches many years and only saw a few get noisey bearings but never saw one fail electricly.

15 minute break!

Just spoke to my electric shop guy, says go with the Balmar have the regulator set to 14.5-14.9 ans go boating. He said battery quality is important to. He said I worked on to many complicated cruising boats and was muddying the issue.
He did say you may also want to look into the link below.

http://www.powermastermotorsports.com/