Battery Charger for a Standby Generator

[CuriousElectron]

Hello All,
Has anyone used a DC to DC converter in the past as battery charger to charge 12VDC battery on a genset? The project I'm working on doesn't have a reliable 120vac supply on site, but there is battery bank that can be used to maintain charge on the generator battery. Looking for 24VDC to 12VDC battery charger. Genset vendor is not able to source the DC battery charger.
Has anyone done something similar in the past? Looking for ideas & thoughts, as I understand we would have to spec out a suitable BC to match generator vendor provided battery.
Thanks!
EE

 

[waross]

Years ago I did a unique installation in the Jungle of the Moskito Coast or The Moskitia. (The spelling varies, The name derives from the indigenous Moskito inhabitants, not from the insect.)
This was a four bed hospital that was the primary access to health care for an estimated 10,000 persons spread throughout the jungle.
My project was to install a new diesel generator and to generally tune up the existing electrical system.
The existing system was a conglomeration of solar, wind and diesel power.
When the sun was shining, the solar panels supplied about 50 or 60 Amps to the battery bank.
There was an inverter to supply 120 Volts 60 Hz to the hospital complex.
When the generator was running, the inverter supplied about 50 or 60 Amps to the the battery bank.
The the new diesel generator originally had a 10 Amp battery charging alternator. I had that replaced with a 60 Amp alternator.
A wind charger supplied about 15 Amps to the battery bank.
An existing problem was chronic failures of the inverter.
When the inverter failed, it was sent to the manufacturer in the US for repair.
There were two inverters and one was almost always out for repair.
The problem was diagnosed as high voltage transients picked up by the wind charger down-leads whenever there was a lightning strike within several miles.
Looking at the system, with the generator running, there would be about 150 Amps to 180 Amps of charging current.
The wind charger added about 15 Amps.
I de-commissioned the wind charger and it was never missed.
Now taking the weave back to our problem, there generator starting battery was kept separate from the main battery bank.
With the alternator on the diesel connected to the main battery bank the starting battery needed to be charged.

A small 120 VAC to 12 VDC charger was connected to the 120 VAC output of the generator.
Whenever the generator was running, rather than a set mounted alternator charging the battery, the battery charger charged the battery.

Specific comments.
The battery on the diesel engine should hold a charge for months. If not, replace it.
Beware of charging the battery when the engine is not running.
If the engine is operated as is, with no external charger, the battery will eventually fail, the set will not start and the battery will have to be replaced.
If an external charger is used when the set is not running, eventually the battery will fail, but the continuous charge will allow it to still start the engine.
PS. After cleaning up the mess when more than one battery exploded, I went around to all of my standby generator customers and disconnected the internal battery charger supplied as part of the control panel. No more exploding batteries.
The battery will continue to deteriorate.
Eventually the battery will explode rather than start the set, the set won't start, you will have to clean up a lot of sulfuric acid from the generator room, and you will have to replace the battery.
Is it worth the trouble to get a couple of extra months of life from a failing battery?

Recommendations:
1. Leave the set as is with the included 12 volt alternator charging the battery.
2. If that is not possible, arrange a 120VAC/12VDC charger to charge only when the set is running.
3. If you really persist in a continuous charge to the battery, use a light bulb.
A 12 Volt incandescent lamp connected between the 24 Volt battery and the 12 Volt battery will trickle charge the battery and you will always have lights on in the generator room. (I have seen a number of commercial fishing and lobster boats with 32 Volt electrical systems use this technique to keep a 12 Volt battery charged for the electronics.)

 

[dpc]

This is pretty commonly done on marine applications these days with people going with Lithium house batteries but keeping a lead-acid starting battery. I'd check with marine electrical suppliers, even West Marine should have these. Victron is a common brand in this market. I see they have a 24 V to 12 V unit. I have no direct experience, but it is certainly possible, and you shouldn't need much amp output to keep the starting battery charged.

 

[EdStainless]

There are battery maintainers that will not cook a battery.
Check with a marine supplier if you want to go this route.

 

[3DDave]

Would it be more worthwhile to get a battery tester to check internal resistance and state of charge? If the goal is to not be surprised that the battery won't start the generator, knowing what the battery is capable of over time seems superior to splicing in a charging solution.

 

[TugboatEng]

You have a lot of options. You can convert the engine to 24V. Or, you can transform to 24V to 12V, there are tons of options available. If you have compressed air or natural gas on site you can use that for starting.

 

[waross]

Tens of thousands of standby generators are operating with the "As supplied" battery and engine mounted alternator.
What is special about your site that you cannot use the set as supplied, as everyone else does?
What charges the 24 Volt battery bank?
Read my lips:
"If you have a charger permanently connected to the battery of a standby set, there is a good chance that it will one day explode.
It is fortunate that there was never anyone near the set when the sets I serviced exploded. When the accumulated Brown Gas detonates in the battery, it typically removes the entire top of the battery case. It is quite violent.
I was nearby when a battery exploded in a car. The small plastic fragments that used to be part of the top of the battery case put small dents in the hood, from the inside out."

 

[LittleInch]

Does the battery bank consist of two 12V batteries in series?

If so just take a feed direct tot he engine from on of those batteries.

but you need a specific floating charge battery management system if you're going to avoid the exploding battery situation.

Or go solid state (LiFePO)

But 24V to 12V battery chagers appear to be commonplace, if a bit pricy. Also look into the RV world - many seem to be dual 24 / 12V systems.

Or just run it through an invertor and then back again to DC.

 

[waross]

but you need a specific floating charge battery management system if you're going to avoid the exploding battery situation.

That is a great solution for a healthy battery.
But when a battery fails to the point that one cell shorts out, the remaining cells are overcharged and generate Brown's gas, an explosive mixture of hydrogen and oxygen.
The next attempted start, BANG.
Been there, done that, cleaned up the mess and have the tee shirt.

 

[IRstuff]

A battery charger is not just a voltage supply, particularly if you do not want to damage the battery. You need a battery management system that figures out whether the battery is charged, and if so, decrease, or stop, the voltage to maintain proper charge levels. Additionally, it should be able to detect if the battery has damage or other issues.

 

[waross]

Manufacturers of standby sets typically include a good quality float charger in the control panel.
I have seen several batteries explode, but never when the charger was disconnected.