Generator Battery Poll 1

[itsmoked]

In your experience what's the mix on emergency generators and pumps for starting energy storage.

Battery voltage: 12 or 24V?
Battery type: Lead Acid or NiCd?
Any other relevant points?

If the batteries are 24V are their Amp-Hr ratings proportionally reduced from their 12V brethren?

Keith Cress
Flamin Systems, Inc.-

http://www.flaminsystems.com

 

[ScottyUK]

Most gennys I deal with are 24V. The batteries are usually about as big as you will get in a 12V block. Our fire pumps have redundant 24V banks on single cell Ni-Cads. 12V is uncommon except on really small portable sets in my experience.


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Sometimes I only open my mouth to swap feet...

 

[catserveng]

Most all the generators we service above 100 ekW are 24 VDC, and starting batteries are typically group 28, 4D or 8D's. On large units, 2-2.5 MW we use high capacity series paralleled groups of 4 8D's.

All of our UL listed fire pumps are 24 VDC, usually with two 4D batteries as standard.

On units below 60 ekW we typically use 12 VDC systems. Between 60 and 100 is a mix and depends on desired attachments.

Most are lead acid, occasionally we see NiCad's for starting service, but really don't seem to be worth the extra cost when we take service life, maintenance, and initial cost into account, at least based on our experience.

Hope that helps.

 

[ScottyUK]

Agree with CatServEng regarding lifetime costs of NiCads - we will be replacing them with lead-acid types soon: even if we have to replace the lead-acids every three years the lifetime cost will still be lower over 20 years. Just need to convince the insurers now...


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Sometimes I only open my mouth to swap feet...

 

[waross]

My customer base is generally not constrained by insurance issues and doesn't pay for NiCads. Other than that I agree with catserveng. I used to service a group of 5, (3 x 350 KW and 2 x 600 KW) sets that were on air start. There was a common receiver and a 10 or 15 Hp. electric compressor. The back-up was a hand-start, 2 cylinder diesel powered air compressor.
all but one 600 KW are now out of service. I haven't seen air start on anthing new.
respectfully

 

[dpc]

Nearly all are 24 V and Lead-Acid.

 

[waross]

Are you interested in a particular size of engine Keith?
Respectfully

 

[Hoxton]

Most high speed (1500 / 1800 rpm engines are dc start. A few are air start for mainly historical reasons.

Medium (1000 rpm) and slow speed (< 750 rpm) are air start, because of the energy required to get them up to firing speed. Batteries would be immense.

Strangely, here in UK we see some "continental" CHP gas engine sets with "mains starters" - these are basically transformer recifier units to give 24V dc from the mains. Us brits do not see the point, as my service manager said to me recently, "even YOU could go down the local garage, buy batteries and replace them.... why this useless technology..."

There you go!

Back to the point, lead acids are known technology and work in a variety of environments and are cost effective. Cannot see the point of NiCad - surely these have to be discharged regularly to maintain life?

Air start only on large engines - this gets you into pressure vessel regulations and all sorts of problems. It is so easy to make it complex....

By the way amp - hours is not a requisite for start batteries - it is the crank and inrush currents at minimum ambient teperature that defines the battery size. A-h is a constant slow discharge figure - no use on a genset start application.

 

[itsmoked]

Thanks for the info. As you guys may have noted elsewhere I am designing a charger for the starting batteries of emergency diesel engines, mostly pumps. The charger handles both 12V and 24V LA and optionally, in a future SW rev, NiCad.

The target is 10A into a 12V battery. I'm 'kind' of expecting that an equivalent 24V system would only need about 1/2 the current e.g. 5A for a similar system/performance. Size wise I imagine,(while not positive), under about 500HP. Perhaps someone,(catserveng), could suggest a typical fire pump size found in building protection.

Keith Cress
Flamin Systems, Inc.-

http://www.flaminsystems.com

 

[ScottyUK]

Keith,

Our fire pumps are about 700 HP each, although they are protecting a big industrial facility so you size estimate is reasonable. You could ask the guys who really know in forum184.


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Sometimes I only open my mouth to swap feet...

 

[catserveng]

As a "typical" standard,

Mechanical governed small units (usually below 100ekW) we use 12 VDC 6 Amp, on electroincally governed or electronically controlled we go up to 10 amps.

24 VDC units, 10 amp on mechanical engines, 20 on electronic engines.

Standard on the UL fire pump packages we sell is 24 VDC 10 amp.

Just a few notes if you're designing,
A cutoff during crank so the charger doesn't spike the engine electronics. This has been a real problem with some of the less expensive chargers used on new engines with electronic controllers.

As yet no one provides an output "clamp" so if a tech or maint person opens the battery circuit under charge the charger doesn't spike the electronics, you'd be surprised how often that happens, even with big signs and repeated failures.

Almost every charger we buy has a minimum of three alarm outputs on form C contacts, Summary alarm, Low DC volys, and AC fail, there are others possible but those are the ones we use the most.

Make the float adjust pot easy to get to, be amazed how many manufacturers make this a bear to get at and safely adjust.

Good luck.

Regards,

 

[itsmoked]

Thanks Scotty for the forum tip.

catserveng; Greatly appreciate that little walk through charger land!

Keith Cress
Flamin Systems, Inc.-

http://www.flaminsystems.com

 

[JBinCA]

24V Lead acid on almost every gen I see in. Mostly in California and Hawaii, in the 500 to 3000 kVA range.

Regards,

JB

 

[alehman]

Fire pumps range from 20 hp to 1000's. I agree probably 95% are 24V lead-acid. I've only seen a few nicad's in my 15 years and I don't recall any 12V systems.

For generators, NFPA 110 requires specific monitoring contacts. Also there are ETL listing requirements. Don't forget to provide auto-equalize and auto temperature compensation. Batteries and chargers are one of the most common causes of failure of diesel engines. Make it reliable!

 

[waross]

Hi Keith;
This paragraph concerns under 100 KVA machines.
All of the under 100KVA (200KVA?) machines that I see have an automotive style alternator to charge the battery. The alternator also serves to keep the fan belt tight and provide a point of adjustment for the fan belt. The alternator quickly replaces the starting energy to the battery.
Any electronics powered by the battery is able to withstand load dump voltages and I have never had a problem with battery disconnects when running. Some sets may not run with the battery disconnected but no permanent damage is done.
I believe that the load dump voltage of an automotive alternator may produce transients far in excess of the voltages of an open circuited battery charger and the set electronics are able to survive load dumps.
Still I spec battery chargers for these sets. The charger is usually rated at 1 A or 2 A. The purpose is to ensure that the battery does not self discharge between runs. The charger must be able to self limit its output so as not to fail if it is connected to a large battery in a poor state of charge. I have destroyed every small automotive charger that I have used. Trickle chargers, motorcycle chargers, boat trickle chargers. I have learned my lesson and no longer use small automotive battery chargers for permanent applications. Your charger should be able to withstand running for long periods at maximum output into low impedance loads.

The following comments are a "work in progress" or a discussion point.
What would I like to see in a battery charger?
How about monitoring cranking voltages and times? Once a benchmark has been set, extended cranking times and or lower cranking voltages may be an indication of reduced battery performance and a need for maintainance or replacement of the battery.
If we are monitoring anyway, let's monitor recharge times also. If the engine mounted alternator is taking longer than usual to replace the starting energy it may be an indication of battery problems or also an indication of slipping fan belts or one or more failed diodes in the alternator.
There are lots of suitable battery chargers available for diesel engines. How about a charger that anticipates and alarms for impending battery and alternator problems?
Comments and suggestions are welcome friends.
Respectfully

 

[itsmoked]

JBinCA; Thanks.

alehman; Thanks for those related heads-up too.

waross; Great points! I can easily include the crank voltage monitoring. It's a great idea. We had a battery test resistor but had to throw it out due to its nasty cost. Also the variety of batteries and machines made it less than perfect at divining capacity and charge state values. But, monitoring the results of actual starts is really the last word.

I agree a 2A charger is the perfect device, BUT! NAFTA requires the charger to "fully charge the battery within 24hrs". Never mind, they don't really state what battery. I suppose some engines might lack an alternator.

I'll give another check on the load-dump front of my charger.

Keith Cress
Flamin Systems, Inc.-

http://www.flaminsystems.com

 

[ruggedscot]

Why put an alternator on when you ave a pretty big un attached to the back of the diesel, just step the line down and rectify and you have a redily availiable charger to replenish the battery.

All the diesels Ive seen have been 24v some with double starters and some with single starters...

Rugged

 

[itsmoked]

ruggedscot; Double starters! I've personally never seen that and thought two batteries and one starter? Back to a single point failure.
Glad to hear they exist.

Often an E. generator may not have 120 or 240 to run a charger. Also if it is a fire pump...

Keith Cress
Flamin Systems, Inc.-

http://www.flaminsystems.com

 

[ScottyUK]

Keith,

Many big engines designed for stationary applications like fire pump and standby generation have the option of dual starters. There are two mounting points, one either side of the flywheel housing. Each motor usually has its own battery. One really big multi-MW sets maybe two are required due to the size of the engine - I've never really questioned it. I suppose sharing duty reduces stress on the starter pinion and ring gear too.


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Sometimes I only open my mouth to swap feet...

 

[bogeyman]

Dual starters are used to reduce wear and tear in frequent start systems employing larger engines the starters are electicaly connected to power up simultaneously.
A diversion,
How about the clock work spring starter for emergencies when the 24v goes flat, Its got a huge spring of belvile washers and a lead screw to turn the output shaft
there is a nice gearbox to ease winding up the thing which takes all the effort you can muster for a minute or two.
They are used in construction plant without electrical systems and on intrinsicaly safe installations.