How to get high charging rates from a generator

[sailingharry]

A friend has a new to him Lagoon 45. It has a generator and 800 amp hours of AGM deep cycle batteries. The only way to charge the batteries is through a 40 amp charger. This is clearly inadequate!

I have seen over 70 amps into my 200 amp hour golf cart batteries. This would lead me to believe that he can support easily 300 amps (maybe even 400) when his batteries are down. The problem is, how?

100 amp battery chargers are the upper end for marine service. It seems to me that to effectively use his generator to charge his batteries from a low state of charge, we need something different. Right now, he is running his generator several hours a day to replenish his batteries.

He has no inverter on the boat, and I am trying to convince him the merits of a 2 KW inverter/charger which will go a long way to improve his charging (they typically have 100 amp or higher chargers) -- but even then, he will be only charging half as much as he could.

I know that automobile chargers are considered death for marine batteries, because they are not designed for extended float. However, a 300 amp industrial automobile battery charger appears to be 2 to $300. Would it be crazy to suggest installing one of these as well, with the understanding that it would only be used when the batteries are well down and high charge rates are desirable. He could turn it on until battery voltage gets to 14 or so, and then turn it off and let the inverter continue the smart charging.

The only other approach I can see is another two or three marine chargers in parallel, which seems somewhat silly.

How do other people effectively charge high amp hour batteries from a generator? It would seem that a need to support 2 to 400 amps of charging rate is not terribly unusual. This could become even more relevant in an era of LiFePo batteries with nearly unlimited acceptance rates.

Harry

[Paul L]

You can tie multiple Victron chargers together.

[john61ct]

800AH AGM bank longevity best served by 150-300A

Sterling, Magnum, ProMariner, Victron, Mastervolt, Samlex, Outback

Adjustable custom setpoints voltage is critical for future chemistries.

All can be "stacked" in parallel, some designed to be but not important IMO.

I prefer stand-alone chargers, not Combi style integrated with inverter. But Victron PowerAssist is nice if you do go that way.

Key question, how big a charger load will the generator support?

[sailingharry]

Originally Posted by john61ct

800AH AGM bank longevity best served by 150-300A

Sterling, Magnum, ProMariner, Victron, Mastervolt, Samlex, Outback

Adjustable custom setpoints voltage is critical for future chemistries.

All can be "stacked" in parallel, some designed to be but not important IMO.

I prefer stand-alone chargers, not Combi style integrated with inverter. But Victron PowerAssist is nice if you do go that way.

Key question, how big a charger load will the generator support?

John,


The charge rate is a classic cruiser dilemma. The lower the charge rate, the longer the batteries last. But at the same time, the lower the load on the engine and the longer it runs. But, even at your suggested 300A, we have a challenge.


I pulled up one credible name, Mastervolt, their largest charger is 50 Amps. I also tried Magnum, no chargers from what I can tell.


I agree with you regarding the benefit of "stacking." Pure parallel works fine, and when something falls off, it's because it isn't needed. Unless you get some sort of harmonic fluctuation going, it doesn't matter. But regardless, 300 Amps is 6 of these 50A chargers in parallel! Is that what people do?


I understand the philosophical objection to combo units, but I've seen them in full time cruise use lasting 20+ years.


I do not know the exact limit or specs of the generator, but it is sized to support the A/C load of a 45 catamaran, so I'm sure it is around 10KW. 300A DC charge is around 4KW AC, give or take some rounding.


So, my question remains -- how do people cram large amps into a battery from a generator? Many people put 150-200A alternators on a main engine, and he's currently limited to 40A on shore power!


Harry

[john61ct]

Sterling goes to 60A. At the high $ end of the market, most unfortunately do go the Combi way.

I suspect most of those looking for hundreds of charging amps do look to native-DC generators / alternators.

Originally Posted by sailingharry

I do not know the exact limit or specs of the generator

Well that would help guide you as to how many to stack.

Or just buy say two to start and test?


> The lower the charge rate, the longer the batteries last

Wut? Categorically false, the opposite is true, especially for quality AGM.

What reason besides longevity would you have for wanting a high (potential) charge rate?

It does not significantly reduce runtime, unless you go to LFP.

You still need solar for the long tail, unless running the genny 6-7 hours is part of the daily routine anyway.

[a64pilot]

Originally Posted by Paul L

You can tie multiple Victron chargers together.

Originally Posted by sailingharry

John,


The charge rate is a classic cruiser dilemma. The lower the charge rate, the longer the batteries last. But at the same time, the lower the load on the engine and the longer it runs. But, even at your suggested 300A, we have a challenge.

First, you can “stack” anybody’s chargers together, I have Balmar, Outback, Sterling and Magnum all charging at once, and they all play together and have no connection to each other.


Second your statement of lower charge rate meaning longer life is incorrect, especially for AGM, but flooded benefits from high charge rates as it stirs the electrolyte.
In fact I think Lifeline wants a min of 200 amps charging for an 800 AH bank and allows an insane 5C which would be 4,000 amps.

I get 185 amps from my Sterling at 60 and my Magnum inverter at 125 for my 660 AH bank. I think there are bigger Magnums, just my 3.5 KW generator can’t support much more than 185 amps at 14.3 V

However due to battery charge acceptance rate, it’s not going to shorten time to FULL charge as much as you may think, you spend most of the time dribbling in amps than you do hammering in big amp loads.

[billknny]

Originally Posted by sailingharry

A friend has a new to him Lagoon 45. It has a generator and 800 amp hours of AGM deep cycle batteries. The only way to charge the batteries is through a 40 amp charger. This is clearly inadequate!

You are right, totally inadequate. Makes me wonder what other inadequacies are hiding in such a system.

Originally Posted by sailingharry

I have seen over 70 amps into my 200 amp hour golf cart batteries. This would lead me to believe that he can support easily 300 amps (maybe even 400) when his batteries are down.

Almost certainly correct. But a key point that is not mentioned is what is hid daily power usage?

Originally Posted by sailingharry

He has no inverter on the boat, and I am trying to convince him the merits of a 2 KW inverter/charger which will go a long way to improve his charging (they typically have 100 amp or higher chargers)

2kW Inverter/chargers typically have a battery charger of 70 amps or so.

Originally Posted by sailingharry

I know that automobile chargers are considered death for marine batteries, because they are not designed for extended float.

There are a lot of other reasons not to use automotive style chargers in a marine environment. Grounding and isolation are typically NOT set up for operation on a boat's electrical system. This is probably a bad and dangerous idea.

Originally Posted by sailingharry

The only other approach I can see is another two or three marine chargers in parallel, which seems somewhat silly.

Why silly? It is a standard way of doing things. There are many good reasons for doing it this way.

First, is wiring. It is a LOT easier to run 3 sets of 1/0 AWG wire to three different 100 AMP chargers than to double up on 4/0 wire which MIGHT be big enough to carry 300 amps for two hours...

Second is shore power. If you could find a 300 AMP charger it would draw close to 40 amps from shore power. It is handy to limit the charging capacity when connected to shore power so you can still run your AC and water heater...

Another advantage is the redundant systems are obviously more reliable.

I assume in the absence of stating otherwise, his system is 12 Volts. I have a 24 Volt 440 Amp-hr system, so the same total power capactiy.

I have a Victron 3kW/70 amp inverter/charger that is used at the dock.

I also have a 100 amp Quick charger that I use together with the Victron only when charging via genset. Makes for a very fast (170 amp) charge, minimizing generator run time. I have Firefly batteries, and they can take that much and more up to 90% SOC. No reason you could not use another 100 amp charger if that was useful or needed.

[sailingharry]

Originally Posted by john61ct

Sterling goes to 60A. At the high $ end of the market, most unfortunately do go the Combi way.

I suspect most of those looking for hundreds of charging amps do look to native-DC generators / alternators.

Well that would help guide you as to how many to stack.

Or just buy say two to start and test?


> The lower the charge rate, the longer the batteries last

Wut? Categorically false, the opposite is true, especially for quality AGM.

What reason besides longevity would you have for wanting a high (potential) charge rate?

It does not significantly reduce runtime, unless you go to LFP.

You still need solar for the long tail, unless running the genny 6-7 hours is part of the daily routine anyway.

John,

I think we are crossing signals.

With regard to generator, I was trying to convey that it is almost certain to be several times larger than anything the batteries could ever take.

With regard to charging current, I know that more is good -- to a point. I am a FLA guy so AGM is new to me, but the net implies 20-30% of capacity -- or 160-240A max. I am nearly certain they will accept over 300, maybe 400, if the charger will provide. Your comment regarding 150-300 led me to believe you were cautioning against allowing 400 or more.

With regard to rum time, you are absolutely right on FLA. I thought an advantage of AGM was a longer bulk phase (more ah before it shifted to acceptance) But in either type, 100A will give a LONG bulk phase!

Native DC? Do folks use two generators, or a big inverter to power typical generator loads like A/C?

[Albro359]

We have a 660 Ah bank consisting of 12 6V 220Ah AGM batteries wired in series-parallel for a 24V system.

We have a 7.5kVA Onan genset that runs a 100A Victron charger and a 30A Promariner charger.
We have a 175A alternator on the main engine and 600W of solar panels.
The solar panels are permanently "on" through an MPPT controller.

Batteries are bulk charged either by the engine alternator when motoring or the Onan when at anchor.

At times when the batteries have been quite low we have everything running.
Together than can be around 300A.

We monitor the charging current as it goes down we turn off chargers that are not needed.


It all works very well

[billknny]

Originally Posted by john61ct

Sterling goes to 60A. At the high $ end of the market, most unfortunately do go the Combi way.

There are actually many brands making charger only that spec out significantly greateer 60 amps. Of course they are all expensive, and not available on the shelf at your local west marine.

Dolphin makes 90 amp for 12 V and 100 amp for 24 volt.

Quick makes 100 amp for 12 and 24 volts

Victron also makes 100 amp chargers.

[smac999]

I like the mastervolt 12/100-3 100a chargers. I was playing with a victron 100a charger a few weeks ago and it was not working good at all. it was cutting off at 13.8v (measured at charger posts). so we were only getting 40a out of it in bulk when combined with a 2nd charger. with batteries at ~14v. should have been putting out 100a

I install a lot of magnasine inverter chargers + 100a mastervolt chargers for 200a charging.

you also need to check the gen size. 100a of charing is about 1.5kw of AC.

if you only have a 3k gen. 2 100a chargers will max it out and you can't run anything else. which is the nice thing about one of them being an inverter / charger. as it'll cut back charging if loads are added.

[john61ct]

Originally Posted by sailingharry

With regard to generator, I was trying to convey that it is almost certain to be several times larger than anything the batteries could ever take.

With a large high CAR bank that is not to be assumed.

.8C acceptance is common for short timespans when well depleted, so for 800AH AGM, 600+A is likely to be seen and not a problem assuming robust infrastructure and overtemp protection.

Max current ratings can in that case be ignored, more a general CYA liability thing than physical limitation.

.4C (320A) is the minimum recommended for longevity by some makers, .2C by others, likely for marketing reasons.

> Your comment regarding 150-300 led me to believe you were cautioning against allowing 400 or more.

Did not mean to imply that. More that investing past that point would give lower returns.

> I thought an advantage of AGM was a longer bulk phase (more ah before it shifted to acceptance)

That depends on current rate. Total charge time will still need to be 5-7 hours when getting to 100% Full.

> But in either type, 100A will give a LONG bulk phase!

Going from 100A to 200A will shorten Full charge total time by 20-40 minutes.

For cycles where getting to 100% is not required, or given some solar to finish the long tail, it may cut runtime in half.

> Native DC?

I was talking alternators or "DC generators" for bank charging purposes.

It would not be a technical challenge to go big enough to run large AC loads like aircon, but that is rarely done.

There are native DC aircon systems though, the ones I've heard positive reports of are 48V though.

[ayates]

I have two Victron 60A Skylla chargers running in parallel to a 740 AH FLA house battery bank. With no house loads, I get a full 120A into the batteries.





Allan.

[john61ct]

That's right-sized for FLA, but much lower than ideal if the bank were AGM.

[Jammer]

Originally Posted by sailingharry

I also tried Magnum, no chargers from what I can tell.

Magnum sells inverter/chargers. The idea is that you purchase an inverter/charger that is sized to provide whatever charging capacity you need, and the inverter capability comes along for the ride. They offer a 12v 4kw inverter charger that will charge at around 200 amps, if I recall correctly.