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Twin battery chargers

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Good morning. Is it possible to connect two battery chargers of the same make and output to increase the charge capabilities. 

Thanks. 

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22 minutes ago, fudd said:

Good morning. Is it possible to connect two battery chargers of the same make and output to increase the charge capabilities. 

Thanks. 

In general  -'No'

 

I tried that once with no effect. I even tried putting a diode on each output to 'hide each charger from one anather'.

 

I'm sure somebody will be along shortly to contradict me..

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27 minutes ago, fudd said:

Good morning. Is it possible to connect two battery chargers of the same make and output to increase the charge capabilities. 

Thanks. 

It is only the same as having 2 alternators going into one bank.

The battery chargers don't need to be identical & it is DC so no phasing problems,. Each charger will be set to a maximum output voltage (say 14.4v) but one will inevitably be slightly higher than the other, once the lower voltage is reached the 'low voltage' charger will shut down and the other one will continue to charge.

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28 minutes ago, fudd said:

Good morning. Is it possible to connect two battery chargers of the same make and output to increase the charge capabilities. 

Thanks. 

People do it all the time with alternator and solar charging.

 

More info: During the first stage of charging well discharged batteries thee batteries will accept far more current than the charge source(s) can provide. The high current is likely to pull the charger voltage down so two chargers will work together. As the batteries charge they will accept a lower and lower charging current so the charging voltage rises until the charger starts to regulate the voltage (acceptance charge). At this point one charger may well go into float because the other charger has  a higher regulated voltage so it would appear that having two charges make no difference. If the chargers pulse the voltage they could even swap the charging between themselves. At that point one can only guess what is going on.

 

I suspect @OldGoat may have tried it on fairly well charged batteries.

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1 minute ago, Tony Brooks said:

People do it all the time with alternator and solar charging.

 

More info: During the first stage of charging well discharged batteries thee batteries will accept far more current than the charge source(s) can provide. The high current is likely to pull the charger voltage down so two chargers will work together. As the batteries charge they will accept a lower and lower charging current so the charging voltage rises until the charger starts to regulate the voltage (acceptance charge). At this point one charger may well go into float because the other charger has  a higher regulated voltage so it would appear that having two charges make no difference. If the chargers pulse the voltage they could even swap the charging between themselves. At that point one can only guess what is going on.

 

I suspect @OldGoat may have tried it on fairly well charged batteries.

Absolutely.

My batteries are always in a good state of charge and it would take ages (and a fair amount of difficulty) to discharge them 'completely'.

I did the best that I could, yer 'onour....

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Just now, OldGoat said:

Absolutely.

My batteries are always in a good state of charge and it would take ages (and a fair amount of difficulty) to discharge them 'completely'.

I did the best that I could, yer 'onour....

So I suppose the short answer is "only for a fairly short while".

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1 minute ago, Tony Brooks said:

So I suppose the short answer is "only for a fairly short while".

Short answers are not quite the style of this forum....

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The reason I’m asking is that I’m researching hybrid drives. Big lithium 48v battery bank, dc generator and some sort of electric motor. That is the basic idea. I’ve looked into dc generators and most of them seem to run at 2-3 k rpm and I’ve always been advised against high revving generators. So, my next thought was to-maybe go for a fairly large low revving A.C. generator and charge the batteries this way. I’ve looked at Victron 48v chargers and the biggest would seem to be 50 amps. This would take ages to charge a fairly large bank of batteries. I’m into the silent aspect of cruising. I’m not being ‘green’ although I do respect that point of view and I’ve read up on the conversion losses involved and realise that it’s not the way to go regarding fuel economy. My point of view is, if you can hear the engine then it’s got to sounds nice, or not hear it at all. I got quoted £30K for a vintage engine and thought for that money I may be able to go the silent route. 

Thanks again. 

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29 minutes ago, Tony Brooks said:

So I suppose the short answer is "only for a fairly short while".

It’s the same (disappointing) answer to the question ‘if I replace my 50A charger with a 100A charger, will it halve the charging time?’, sadly no.

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Have a look at the 48-volt victron Inverter / Chargers they have high output battery chargers. 

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1 hour ago, fudd said:

Good morning. Is it possible to connect two battery chargers of the same make and output to increase the charge capabilities. 

Thanks. 

 

Assuming a lead acid battery bank, then only if the capacity of the battery is big enough, and then only in the bulk stage of the charge when the battery will accept large a charge current.

 

When I was working on the tools, we often parallelled two or three 2000 amp rectifiers (chargers) to charge a 15,050Ah battery at up to 5000 amps for the bulk stage of the charge.

 

However it is essential that the voltage outputs of the chargers match to a few millivolts, or the chargers will not load share equally.

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1 hour ago, OldGoat said:

In general  -'No'

 

I tried that once with no effect. I even tried putting a diode on each output to 'hide each charger from one anather'.

 

I'm sure somebody will be along shortly to contradict me..

 

That's not my experience.

 

About 14 years ago I just had a 30amp Sterling Pro-digital batter charger but I wanted to up the output to run from a generator. I was thinking selling it and fitting a bigger charger but then I spoke to someone from Sterling and he told me I could just add another charger. I bought and installed a 40amp Sterling Pro-digital charger and they both work fine and at startup I see 70amps going into my batteries on my battery monitor. When the output drops below 30amps I switch the 40amp charger off.

 

When I'm on shore power I just use the 30amp charger which has one of the three 12v outputs connected to my start battery. All the other outputs on both chargers are connected to the domestic bank. You must use all outputs from a charger, so in general if a battery charger has 3 and you only have 2 battery banks you should link two of the output terminals and connect that to the biggest bank..

 

Edited by blackrose
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Thanks for your help. 
What would be the best way to achieve what I would like to do?  I’ve been advised that I need about 1000ah lithium battery bank.thanks again. 

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1 minute ago, fudd said:

Thanks for your help. 
What would be the best way to achieve what I would like to do?  I’ve been advised that I need about 1000ah lithium battery bank.thanks again. 

1000Ah at 48 volts, (or 1000ah at 12v) ?

 

I hope you have very deep pockets - that will far, far, far exceed the cost of a 'built in' 1500rpm generator (£8k-£10k inc installation)

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6 minutes ago, fudd said:

Thanks for your help. 
What would be the best way to achieve what I would like to do?  I’ve been advised that I need about 1000ah lithium battery bank.thanks again. 

There are lots of threads on here about lithiums and charging lithiums, and a few people making there own systems. It all gets very complicated and some sort of controller is really needed. Its critical to avoid over charging so ideally the electronics inside the battery needs to talk to the chargers to tell them to stop charging when the batteries are full, or moderately full if you want maximum battery life. It can be done but it does get a bit complicated and expensive.

If you are going 48volt then some of the domestic "Tesla Powerwall" type things work out much cheaper than 12 volt systems but you would need to check that they can handle large currents if that is required.

 

.................Dave

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28 minutes ago, Alan de Enfield said:

1000Ah at 48 volts, (or 1000ah at 12v) ?

 

I hope you have very deep pockets - that will far, far, far exceed the cost of a 'built in' 1500rpm generator (£8k-£10k inc installation)

48v. The generator will still need a charger. 

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21 minutes ago, fudd said:

48v. The generator will still need a charger. 

I know - its frightening £20k for batteries, £10k+ for a generator* £2000 for a 48v 200a charger + BMS

Total = 1 arm and 2 Kidneys.

 

48 Volt 200 Amp 3 Phase | Forklift-Battery-Charger.com (forklift-battery-charger.com)

 

(Yes I know its 3-phase, "Different power supply voltages available on request").

 

* It would need to be a 10KVA generator as a minimum to power a 200amp charger

Edited by Alan de Enfield

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There is going to be a lot of stored energy in a battery boat, and a lot more being generated when recharging. 

 

All this is getting to be  well outside the ken of most marine electricians.  

Not being much of a high power or MV electric engineer I should want to see that a proper electrical engineer followed a good design strategy to ensure that the equipment  and the controls was all safe,  not going to cause corrosion problems and adequately documented so it can be diagnosed and safely mended when (not if) it goes wrong.

 

N

 

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2 hours ago, blackrose said:

 

That's not my experience.

 

About 14 years ago I just had a 30amp Sterling Pro-digital batter charger but I wanted to up the output to run from a generator. I was thinking selling it and fitting a bigger charger but then I spoke to someone from Sterling and he told me I could just add another charger. I bought and installed a 40amp Sterling Pro-digital charger and they both work fine and at startup I see 70amps going into my batteries on my battery monitor. When the output drops below 30amps I switch the 40amp charger off.

 

When I'm on shore power I just use the 30amp charger which has one of the three 12v outputs connected to my start battery. All the other outputs on both chargers are connected to the domestic bank. You must use all outputs from a charger, so in general if a battery charger has 3 and you only have 2 battery banks you should link two of the output terminals and connect that to the biggest bank..

 

About 20 years ago I bought a 2nd hand, unused Sterling "4 Stage" charger rated at 150amps. It had 2 a/c imputs and 2 on/off switches together with 2 state of charge indicator panels. In effect 2 x 75 amp chargers. The DC outputs could be configured  for 1 or 2 battery banks. God knows how old it was and I was never able to track down an installation/user manual.  

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3 hours ago, fudd said:

The reason I’m asking is that I’m researching hybrid drives. Big lithium 48v battery bank, dc generator and some sort of electric motor. That is the basic idea. I’ve looked into dc generators and most of them seem to run at 2-3 k rpm and I’ve always been advised against high revving generators. So, my next thought was to-maybe go for a fairly large low revving A.C. generator and charge the batteries this way. I’ve looked at Victron 48v chargers and the biggest would seem to be 50 amps. This would take ages to charge a fairly large bank of batteries. I’m into the silent aspect of cruising. I’m not being ‘green’ although I do respect that point of view and I’ve read up on the conversion losses involved and realise that it’s not the way to go regarding fuel economy. My point of view is, if you can hear the engine then it’s got to sounds nice, or not hear it at all. I got quoted £30K for a vintage engine and thought for that money I may be able to go the silent route. 

Thanks again. 

 

Now you give the vital bit of information - lithium bank. The answer for those will be different because they wil accept as much current as you can throw at the for the whole of sensible charging period so in this case - yes, bith cahrgers will deliver their maximum output until the Lithium charge controller stops charging.

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Thanks for the input. I do like Victron chargers because had one on my boat when I bought it, but I’m open to any suggestions for any other make. I’d like to pump in as much as I can and would buy the appropriate generator. What options do I have?  

Ive not ruled out Alan de Enfield’s approach but would prefer something more ‘maritime’ So to speak. 

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4 hours ago, blackrose said:

 

That's not my experience.

 

About 14 years ago I just had a 30amp Sterling Pro-digital batter charger but I wanted to up the output to run from a generator. I was thinking selling it and fitting a bigger charger but then I spoke to someone from Sterling and he told me I could just add another charger. I bought and installed a 40amp Sterling Pro-digital charger and they both work fine and at startup I see 70amps going into my batteries on my battery monitor. When the output drops below 30amps I switch the 40amp charger off.

 

When I'm on shore power I just use the 30amp charger which has one of the three 12v outputs connected to my start battery. All the other outputs on both chargers are connected to the domestic bank. You must use all outputs from a charger, so in general if a battery charger has 3 and you only have 2 battery banks you should link two of the output terminals and connect that to the biggest bank..

 

That last sentence, very sage advice folks. 👍

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5 hours ago, blackrose said:

You must use all outputs from a charger, so in general if a battery charger has 3 and you only have 2 battery banks you should link two of the output terminals and connect that to the biggest bank..

 

15 minutes ago, BD3Bill said:

That last sentence, very sage advice folks. 👍

But that does not apply to all chargers.

 

My Victon manual says that 100% can be achieved from any one terminal, and is 'split' as the number of battery banks are connected.

 

Operation

The battery charger charges the battery with 3-stage (Bulk-Absorption-Float) charging characteristic. It can remain connected to the battery continuously, without increased gas formation, caused by overcharging, taking place. The charger can be used for different types of batteries but the default settings are for Gel batteries. For use with other types of batteries please select Lead acid or AGM by opening front bottom cover and select dipswitch in bottom left hand corner. See Figure 1. The full charging current of this Charger is divided in three main outputs but any one output can supply 100% of power if that is the only battery connected

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If your generator is 230Vac output not 48V DC (very likely), you can feed it into the mains input of a Victron Multiplus/Quattro and this will charge the batteries, as well as providing AC for the boat. If you want a big charging current you'll need at least a 5kW combo like the Multiplus II 48/5000 which has the advantage of much lower zero-load power drain than the bigger Quattros as well as being considerably cheaper.

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