battery charger max size

Zulane

New member
Joined
11 Jun 2005
Messages
57
Visit site
Main engine 100hp has 1 60 amp alternator and 1 120 amp alternator- so no problem when engine is running.
We have 5 by 105amp Trojan deep cycle batteries for house system. We use a 4kva Fischer Panda Genset for charging at 230v via a Victron 50amp battery charger. Daily use is about 240amps.
We need to upgrade to a new battery charger as large as possible- does anyone know if there is maximum size batt charger so as not to damage the system? Recomended brands?
 

pvb

Well-known member
Joined
16 May 2001
Messages
45,604
Location
UK East Coast
Visit site
Already close to the limit...

If you only have 525Ah of battery capacity, you'll probably be hard-pressed to push much more than 50 or 60 amps into them for any length of time. Do you have a battery monitor which tells you how much charging current there is when the engine's running?
 

Zulane

New member
Joined
11 Jun 2005
Messages
57
Visit site
Re: Already close to the limit...

Hi Thks- yes we have monitor- when using engine the big alternator will start and say 70+amps and gradually stage down but will put a lot of charge in for 2 hours-then gradually slows down to float level- all ok- so thats ok and about the level I need.
The 50amp chger only nets in about max 20amps(with fridge/freezer/lights etc on ) and quite soon say after 1 hour drops right back to net 10-14amps per hour.?
 

William_H

Well-known member
Joined
28 Jul 2003
Messages
13,704
Location
West Australia
Visit site
Re: Already close to the limit...

Hi Zulane the size of the battery charger will dictate the MAX amps you can get into a battery.
The actual voltage of the charger will dictate how many amps the batteries take. (and the charge state of the batteries but not in proportion)
If you are running on shore power 24/7 then the charger should be regulated to 14 volts or even a little less. This will keep batteries fully charged and cope with the drain from services at the same time.
However I take it you are running the battery charger from a generator (genset). If you are running the genset especially to charge the batteries you want as much current into the batteries as possible so you can turn it off soonest. This is acheived by charging at higher voltage so that the batteries will take a higher current up to the limit of what the charger can supply. Higher current however can cook the batteries if it is not reduced when the batteries are charged. So you need an automatic charger unless you are going to switch the genset off after a few hours anyway.

So a larger charger may not actually push more current into the batteries. (or at least not a lot more)

What will get more current into the batteries is bigger batteries. So if you had thought of adding batteries then this will increase the charge current in proportion. ie twice as many batteries will double charge current. Which seems like it may still be in the capabilities of the existing charger.
Double the charge current will halve the charging time necessary because the batteries will be only half as discharged. (not counting natural discharge)
Almost all battery chargers you can buy now are regulated and automatic.

If you really want brute charging current without regulation you need just a transformer and rectifier. The transformer needs to have a secondary of around 15 volts RMS AC. (ideally with several taps so you can adjust)
After rectifying this will give about 18 volts DC pulsed peak voltage.
This will push current into your batteries up to and when fully charged. The current is limited by the transformer resistance and any series resistance you fit. So the transformer needs to be rated at the current you want ie in your case aboiut 1000watts or about 60 amps. (that is pretty big and heavy).
You must have an amp meter. A mechanical analogue type is necessary to accurately measure the average of the pulsing current. You need to have resistance in series to enable you to adjust or limit the current to say 60 amps. The resistors will be about .01 ohm and you will need to be able to switch in 3 or 4 to adjust to your 60 amps.
Each resistor will need to be able to dissipate 40 watts so they will be big and need to be home made (I doubt you could purchase same) (use a section of heavy staineless steel sheet say 12inches long by 2 inches wide.
This set up should push 60 amps into your batteries all the time the genset is running. It will give 12 amps into each of your 5 batteries so over many hours could overcharge and cook your batteries. This style is what old batteries chargers were. They just need to be monitored and turned off.

Sorry about that design waffle. I expect it put you off making a charger. Problem is I doubt you willl find a charger to buy much bigger than what you have. Fact is what you have may be the best option. And if you got one would the batteries take much more current?
good luck olewill Always willing to dicuss by PM.
 

Zulane

New member
Joined
11 Jun 2005
Messages
57
Visit site
Re: Already close to the limit...

thks for detailed technical reply-the issue is only for when on the genset as shore power is 24hr day and even at a low rate the batteries get up eventually.
Am considering a Xandia 120 amp automatic 3 stage charger for genset use.
Difficult to fit more batteries due to space avl.
Will pm with more info later.
 
Top