LITHIUM BATTERIES FOR DUMMIES!

[OceanPlanet]

Originally Posted by a64pilot

Likely less than 10 HP. Direct conversion of 3600W to HP is about 5 HP.
My 3.5 KW generator uses a 7 HP engine.
I’m assuming 12V and 300 amps, of course if voltage is higher, wattage is too, but I bet 10 HP guess is conservative.

Probably better to guess higher than lower. Note that alternators do vsry greatly in efficiency. 50% is considered quite good.

As noted above, at higher voltage, efficiency generally increases.

[newhaul]

Originally Posted by kmacdonald

The general rule of thumb for an alternator is 1 HP for 25 amp output. Google will confirm.

Google may say that but alten generators says 300 amps 12 volt with 9.9 horse hatz diesel engine.
https://www.altendc.com/diesel-batte...-dc-generators
Available Output:
12 volt / 300 amps / 3.6 kW
24 volt / 160 amps / 3.8 kW
48 volt / 100 amps / 4.8 kW

Fuel Consumption:
0.52 Gal/hr
2.00 L/hr
(@ 75% load)

Engine Model
Hatz Diesel 1B40

Engine Output
7.3 kW
9.9 HP

[kmacdonald]

Originally Posted by newhaul

Google may say that but alten generators says 300 amps 12 volt with 9.9 horse hatz diesel engine.
https://www.altendc.com/diesel-batte...-dc-generators
Available Output:
12 volt / 300 amps / 3.6 kW
24 volt / 160 amps / 3.8 kW
48 volt / 100 amps / 4.8 kW

Fuel Consumption:
0.52 Gal/hr
2.00 L/hr
(@ 75% load)

Engine Model
Hatz Diesel 1B40

Engine Output
7.3 kW
9.9 HP

That's about right for 12V. Alternators put out about 14.4V give or take. Correcting for that I get 11.88 HP for 300 amps @ 14.4V
The rule of thumb gives 12HP. Isn't that close enough?

[kmacdonald]

Originally Posted by a64pilot

Likely less than 10 HP. Direct conversion of 3600W to HP is about 5 HP.
My 3.5 KW generator uses a 7 HP engine.
I’m assuming 12V and 300 amps, of course if voltage is higher, wattage is too, but I bet 10 HP guess is conservative.

An AC generator and a DC alternator are two different animals. A DC alternator first produces AC and rectifies it to DC. There are losses in that process. The rectifiers are actually being moved external on some alternators to reduce heat buildup.

Is that a gas powered generator? That's only 500W per HP. A diesel generator can produce about 625 to 650 watts per HP.

[Pelagic]

That's a really interesting number to know for any alternator changes, (which I have just done).
Can you help me ballpark my Alternators HP load on my main engine, so I can better understand a change in top end rpm?
2 x 24v Alternators

1 x 140a (70a @ idle) Mark Grasser for House bank

1 x 70a Balmar for Start Batteries.

What is the HP load for both?

[john61ct]

My general deduced ballpark is more like 20A per HP.

Note with a proper VR derating is an option, and you can always cut field current when you want to put all available horses to propulsion

[newhaul]

Originally Posted by kmacdonald

That's about right for 12V. Alternators put out about 14.4V give or take. Correcting for that I get 11.88 HP for 300 amps @ 14.4V
The rule of thumb gives 12HP. Isn't that close enough?

A 12v alternator doesn't put out 12v it does actually put out 14.5 give or take correct but you still call it 12 volt I'm just posting what I know on the generators. I bet it actually puts out 14.5 volt with those 9.9 horses.

So it seems to be 30 amps per horse but 25 per would indeed be a good rule of thumb ( easier to mentally caculate)

[a64pilot]

Originally Posted by kmacdonald

An AC generator and a DC alternator are two different animals. A DC alternator first produces AC and rectifies it to DC. There are losses in that process. The rectifiers are actually being moved external on some alternators to reduce heat buildup.

Is that a gas powered generator? That's only 500W per HP. A diesel generator can produce about 625 to 650 watts per HP.

It’s Diesel, but gas or steam, a horsepower, is a horsepower.
And your correct on the Diodes, they do give of a large amount of heat, and heat requires a lot of power to generate.
However an AC generator also gives off heat, I wonder if it’s close, or is an alternator that much less efficient.
An alternator doesn’t make real DC either, but pulsed DC. I believe a DC generator does make “real” DC.

I have to chuckle a little on people thinking they need a DC generator to charge batteries, where AC generators are much more widely available and probably less expensive.
If you need DC, then how do you charge from Shorepower? With chargers of course, quite likely inverter / chargers.

I’m not saying don’t go to big alternators to forego the need for a generator, just don’t get hung up on thinking you need a DC one. Only advantage I see is a DC generator could be throttled for output to meet demand, where an AC machine normally has to run at X RPM regardless of demand or maintain frequency, but if your charging a Lithium bank, then the load stays high doesn’t it?

[newhaul]

With alternator putting out less than rates I suppose I can get away with a 120amp alternator for my md2 to charge my 200 ah lfp if needed as an oh crap deep winter
Installable unit and run it for an hour or so do i really need an external programable regulator if im trying to recharge 150 or ah of lfp and running for max an hour monitoring the whole time.

[kmacdonald]

Originally Posted by Pelagic

That's a really interesting number to know for any alternator changes, (which I have just done).
Can you help me ballpark my Alternators HP load on my main engine, so I can better understand a change in top end rpm?
2 x 24v Alternators

1 x 140a (70a @ idle) Mark Grasser for House bank

1 x 70a Balmar for Start Batteries.

What is the HP load for both?

At full output of 210 amps at say 28.8V: 15.59HP
I used the data of 160 amps @ 24V with 9.9HP posted above to come up with that figure. It's really close to reality.

If the Balmar is only charging the start batteries it's not putting out 70 amps. The start battery stays at a very high SOC and wont accept much current.


140 amps @ 28.8V=10.4HP

Idle: 70 amps @ 28.8V would be 5.2HP

[kmacdonald]

This doesn't have anything to do with the original question but it needs to be said. When you add external equipment to an engine there is an optimum belt length and pulley sizes to use to prevent some issues beyond the scope here. There are simplified tables to use to determine what is appropriate and what isn't. I suggest you look into it if you are doing this on your own. It's been a long time since I've had to do those types of designs so I'm a little rusty on the matter but if I find time I may find and post some links for more info on it. Just a FYI.

[john61ct]

Any charge source going into LFP should have user adjustability of the setpoints, and other than solar the ability to de-rate current.

[kmacdonald]

Originally Posted by a64pilot

It’s Diesel, but gas or steam, a horsepower, is a horsepower.

Sure it is BUT the torque curves are different. A diesel produces more torque at lower RPM's than a gas engine. The gas engine won't have the torque or HP at lower RPM's to get the generator up to speed without resorting to a higher HP engine. They both will put out the same HP to run the generator once started but a gas engine of that HP won't be able to get it up to speed, the diesel will.

[Q Xopa]

Originally Posted by newhaul

A 12v alternator doesn't put out 12v it does actually put out 14.5 give or take correct but you still call it 12 volt I'm just posting what I know on the generators. I bet it actually puts out 14.5 volt with those 9.9 horses.

So it seems to be 30 amps per horse but 25 per would indeed be a good rule of thumb ( easier to mentally caculate)

Not that it practically helps too much.

The actual formula is- HP=(Watts= Volts x Amps x Efficiency)/ 745.7

of course the trouble with that formula is we dont really ever know exact efficiency. No doubt it varies with heat etc.

Probably the best way would be with our engine on a dyno which of course is not practical.

It's not a particularly important number to know accurately anyway. As long as we understand the concept and have a ball park to make sure our drive belts are up to the task will put us way ahead of the crowd.

Id say the numbers being mentioned seem pretty reasonable.

Also totally agree with Bruces comment about the benefits of going 24V. I have recently done this on mine. The draw backs are that it does add some extra complexity with still having 12V starters and is not quite as common to source parts. 48V would have been even better but it is much rarer and harder to get parts for.

[Q Xopa]

Originally Posted by a64pilot

It’s Diesel, but gas or steam, a horsepower, is a horsepower.
And your correct on the Diodes, they do give of a large amount of heat, and heat requires a lot of power to generate.
However an AC generator also gives off heat, I wonder if it’s close, or is an alternator that much less efficient.
An alternator doesn’t make real DC either, but pulsed DC. I believe a DC generator does make “real” DC.

I have to chuckle a little on people thinking they need a DC generator to charge batteries, where AC generators are much more widely available and probably less expensive.
If you need DC, then how do you charge from Shorepower? With chargers of course, quite likely inverter / chargers.

I’m not saying don’t go to big alternators to forego the need for a generator, just don’t get hung up on thinking you need a DC one. Only advantage I see is a DC generator could be throttled for output to meet demand, where an AC machine normally has to run at X RPM regardless of demand or maintain frequency, but if your charging a Lithium bank, then the load stays high doesn’t it?

Drifting a bit here, but seeing it's mentioned. This does also apply to our main motor and Alternator installation.

Yes AC gens are way more popular, well sort of, used to be. It's getting a bit blurred now as the Honda 2000 inverter style gens I would actually call a DC gen, with an inverted AC output. I know this is actually what is being referred to, which would be a diesel DC gen. But they use the same technology to vary eng rpm according to load which is the main advantage of a 'DC' gen. It seems silly to me to have our AC genset still turning at full (its only) speed even when not loaded.

This is also not very efficient. A diesel, actually any motor likes to operate at max torque rpm and typically 75% of max loading. Here it uses in the order of half the amount of diesel than it does at idle speeds per power unit produced, ie more Amps into our batts for comparatively less, possibly significantly less, diesel burned.

Because most people used them to run their AC power tools or common house hold AC loads.

Any Battery charging will have to obviously need to be DC.

So our choices are-
AC gen- common so cheaper and easier to get parts for, not so efficient, need to convert to DC to charge our batts

DC gen- less common, more efficient, can be smaller for same application, is still changing from AC to DC to charge our batts. This is essentially also our main motor and alternator.

AC Inverter Gens (AKA Honda 2000i etc)- now very common and cheap, fuel, all be it gas efficient, however to charge our batts needs a few AC-DC-AC-DC conversions all with some losses.