battery charging

[Sue1946]

IF I HAVE A 720AMP BATTERY BANK AND WANT TO USE A GENNY TO CHARGE THE BANK DOES THE GENNY HAVE TO BE A SPECIFIC OUTPUT. SAY THE GENNY IS 700WATTS OUTPUT WOULD THIS DO THE JOB. I BELIEVE THE INVERTER FITTED HAS A 100AMP CHARGER BUILT IN.

Edited October 21, 2005 by Sue1946

[tony collins]

IF I HAVE A 720AMP BATTERY BANK AND WANT TO USE A GENNY TO CHARGE THE BANK DOES THE GENNY HAVE TO BE A SPECIFIC OUTPUT. SAY THE GENNY IS 700WATTS OUTPUT WOULD THIS DO THE JOB. I BELIEVE THE INVERTER FITTED HAS A 100AMP CHARGER BUILT IN.

 

 

I could be wrong on this, but no doubt someone will spot it if I am. It will depend on what voltage you are using on the boat. If you are using 24v, the cables can be smaller than those required for 12v. However most people use have the battery bank wired up in parallel producing 12v. So assuming this is correct in your case, here we go. In the following equation V= Volts, A = Amps and W = Watts.

 

so: V x A = W

therefore A = W/V

thus A = 700/12

so A = 58.333r

Assuming you are charging at 12v, the full output of your generator with no efficiency losses, would be 58 amps. I would have thought that this would be more than ample to top up the batteries when required. The inverter may have a charger in-built, but this would be fed from a land line and presumably not used at the same time as the generator. In either case you should make sure that any cabling is of sufficient size to carry the current. If it is not, it could be a fire hazard and it will certainly be inefficient and be subject to voltage drop.

 

Some where in my filing system I have the recommended cable sizes for load, but cannot find it at the moment. However any decent Chandler will be able to advise you on the correct sizes.

 

Hope this helps

 

Tony.

[Sue1946]

I could be wrong on this, but no doubt someone will spot it if I am. It will depend on what voltage you are using on the boat. If you are using 24v, the cables can be smaller than those required for 12v. However most people use have the battery bank wired up in parallel producing 12v. So assuming this is correct in your case, here we go. In the following equation V= Volts, A = Amps and W = Watts.

 

so: V x A = W

therefore A = W/V

thus A = 700/12

so A = 58.333r

Assuming you are charging at 12v, the full output of your generator with no efficiency losses, would be 58 amps. I would have thought that this would be more than ample to top up the batteries when required. The inverter may have a charger in-built, but this would be fed from a land line and presumably not used at the same time as the generator. In either case you should make sure that any cabling is of sufficient size to carry the current. If it is not, it could be a fire hazard and it will certainly be inefficient and be subject to voltage drop.

 

Some where in my filing system I have the recommended cable sizes for load, but cannot find it at the moment. However any decent Chandler will be able to advise you on the correct sizes.

 

Hope this helps

 

Tony.

 

 

I WAS INTENDING TO PLUG THE GENNY ITO THE 240 SOCKET AT REAR OF BOAT THINKING THIS WOULD THEN FEED THE CHARGER IN THE INVERTER

[NB Willawaw]

The genset will provide AC to the charger and the charger will provide either 12V or 24V (depending on what your boat is) and charge the batteries.

Its not a question of whether it will charge your batteries, its a question of whether it will put in more than you take out.

 

To answer your question YES

[Sue1946]

THANKS FOR YOUR REPLIES AS I UNDERSTAND I CAN USE THE GENNY FOR A FEW HOURS ONE AFTERNOON JUST TO TOP UP THE BATTERIES. ALL THAT WOULD BE ON AT THIS TIME WOULD BE MAYBE THE FRIDGE, SO PLENTY WILL BE GOING IN .

[tony collins]

I WAS INTENDING TO PLUG THE GENNY ITO THE 240 SOCKET AT REAR OF BOAT THINKING THIS WOULD THEN FEED THE CHARGER IN THE INVERTER

 

I get it! So your charger is rated at 700W @ 240v! So this means that the output in amp terms is nearer 3 amps! so forget the 58 amps given in the earlier message. I think the generator would struggle to cahrge the whole bank at once, but it might be OK to charge (say) the starter battery if that was flattish. Alternatively if you are running say an electric fridge, then it might be advisable for you to separate out the battery(ies) driving that and charge them separately.

 

Anyone else got any other ideas Guys?

 

Tony

[Sue1946]

THANKS FOR YOUR REPLIES AS I UNDERSTAND I CAN USE THE GENNY FOR A FEW HOURS ONE AFTERNOON JUST TO TOP UP THE BATTERIES. ALL THAT WOULD BE ON AT THIS TIME WOULD BE MAYBE THE FRIDGE, SO PLENTY WILL BE GOING IN .

[Sue1946]

LET ME RE-CAP THE GENNY IS 700W THE INVERTER HAS A 100AMP CHARGER BUILT IN 712A BATT BANK THE QUESTION IS CAN I PLUG THE GENNY IN TO SOCKET AT REAR OF BOAT TO CHARGE BATT. BANK THROUGH THE INVERTER/CHARGER AND WILL 700W GENNY BE POWERFUL ENOUGH TO PUT IN MUCH CHARGE OVER SAY 3HOURS

[Amicus]

Sue, can you give some details of the battery charger? make and model?

[Richard Bustens]

I'm not sure but i would have thought you would need 2500-3000w from the generator to work the charger /combie efficently.

750ah of batteries can be charged at 75 Amps keeping to the 10% law, toget 75 amps out of the combie you would need to be putting 2500w of 220v into it.

 

I think!!!

[Amicus]

Merlin, fer example show a charger with an output of 40A for an input of 650 watts. Take a bit of time on a 700+ AH rig I spose:)

http://www.merlinequipment.com/downloads/B...Info%20Pack.pdf

[Guest]

My findings with 700W genny, 40 amp sterling charger, 550aH battery bank:

 

If batteries are in a fairly high state of charge then the 700w genny copes. If the state of charge is low it needs the bigger 2000w watt genny running. Or run the engine for a short time to give initial boost.

[John Orentas]

A strange enquiry this, not as simple as it first appears. I think you should have a word with the supplier of the inverter. Your generator certainly is not big enough to run a 100 amp charger running anywhere near full output.

 

It could be the case that as the generator does not have sufficient output to drive the charger, the system may simply shut down. Alternatively the charger may use what current is available and charge the batteries at that proportional rate but I am not sure how it could do that.

Edited October 22, 2005 by John Orentas

[Sue1946]

Sue, can you give some details of the battery charger? make and model?

no afraid not as i am just using the specs from a boat i am interested in and am thinking of topping up batteries without running engine. got a thing about running engine while tied up(wear etc)

[Amicus]

no afraid not as i am just using the specs from a boat i am interested in and am thinking of topping up batteries without running engine. got a thing about running engine while tied up(wear etc)

That being the case I think the other posters would agree that a 700W genny is not up to the job. If it could drive a charger the output of said charger would mean extended run times, probably several hours. A 2200 Watt genny is not daft money, there has been discussion on this board in the recent past.

 

http://www.generators.co.uk/briggsstratton/generartors.php

gives some idea

[John Orentas]

A strange enquiry this, not as simple as it first appears. I think you should have a word with the supplier of the inverter. Your generator certainly is not big enough to run a 100 amp charger running anywhere near full output.

 

It could be the case that as the generator does not have sufficient output to drive the charger, the system may simply shut down. Alternatively the charger may use what current is available and charge the batteries at that proportional rate but I am not sure how it could do that.

 

 

I have been advised by Richard B that the it is the convention for the Combi unit to have a setting for the maximum input, shoreline or generator current in your case. As long as you set for a maximum 3 amps the system should work ok and the batteries should then charge at a respectable maximum 35 amps or so.

Edited October 22, 2005 by John Orentas

[Amicus]

John, Sue mentioned a 720A/H battery bank, assume not new, say, 600AH @ 50% charge. How long to a decent charge at 35A?

[John Orentas]

John, Sue mentioned a 720A/H battery bank, assume not new, say, 600AH @ 50% charge. How long to a decent charge at 35A?

 

 

The size of the battery bank is to some degree irrelevant they are only a storage facility after all, a 35 amp charge for boat electrics is more that a good charge rate and is a lot of power in any language. Obviously if more is required more input power is needed.

[Richard Bustens]

John i think that the rheostat and power sharing is only on the victron phoenix multi-plus range, there was no other manufacture making one that could take so much from the land line and top up with the inverter, well that was correct last year may be others now.

[DHutch]

If the battery charger is a (12v) 100amp output one, and as 700w at 12v is about 60amps, then even if the charger is 100% effectient, it wont work.

- The charger will cuting at full-power, and overlaod the genny.

- You will get the situaltion that stan describes, where you need a higher power genny ot the runn the engine to 'get it going'

 

However, if your charget has a 'landline' current limit on it, like some combi units do, you can set this at just under 3amps (700w/240v=2.9amp) and it should work fine.

 

Also, you battery bank is not a "720amp" amp bank, but a 720amp/hour (720Ah) battery bank, this is the Capacity (or "size") of the battery bank, rather then the current it can suppley.

 

 

Daniel

[David]

Hi

Vetus give the following info as an example

A 12v 50Amp charger OUTPUTS 600Watts (thats Volts x Amps = 600W)

All battery chargers are well known to be hungery consumers and need TWICE the Watt's as INPUT so a 12V 50A charger needs 1200 Watt's input from wherever the 240Volt supply is coming. The battery charger is a significant item when working out the size of generator you require (if adding up washing machines, fridges etc that you may want to run of 240V)

Vetus's words not mine.

 

(Mastervolts 12V x 60Amp needs 1100Watt input cos thats one I'm looking at)

 

So in theory your genny needs to be in real life able to supply 240V at 1200W at least as its continous rating for just a charger.

 

Most genny's on the whole give their uncorrected rating as part of the name badge which needs to be corrected for the "power factory" which to keep it simple means in most cases multiply the top rating by 0.8 so a genny badged as say 700Watt would if you read the technical small print be in fact of much lower output.

David