How much can an alternator take before burning up

[grewvin1]

Welcraft 28ft, twin 350's, have two banks of batteries on for house with three large deep draw

• 800 marine cranking amps, 105 amp hours, 185 minute reserve capacity. Used for frige. and house facilities when down to just under 12v when running alternator heats and smells of overheat, have burned out a motorola 105amp on 4hr run. Now have Mando will still heat and smell of overheating will switch over to the other bat's and recharge at home on charger. Is three too many to have on one bank? how many are safe to have?

 

[alldodge]

The ALT should have no problems charging those bats, or even four times that many. You have another issue going on. How are the bats wired and are you using an isolator, ACR, bat switch or other items?

 

[alldodge]

Also check your bats individually, there may be one which has an issue

 

[sam am I]

It's a tough specific spec to find, pretty much hidden as many alt manu's never really say if their output current ratings are either "continuous" or "intermittent" but, the general rule of thumb is that those (most all) alt. max output ratings we see is a manu. spec at intermittent loads and at a certain duty cycle. Turns out typically that that is a full capacity rating that is only a few minutes at a time.......A real world example is a duty cycle (D) of around 5% where duty cycle = (t(on)/(t(on)+t(off)))*100 = % D

e.g., 5% D = 5 min at 105 A full load requires then roughly 100 min no/min load.........Else they'll tend to over heat diodes/windings, etc and can smoke as you've experienced with two alts now.

Definitely check those batts as Dodge mentioned but, with 100A'ish max. alt's, thinking you need to sequence them out as individual batts while charging up if you're taking them all down and/or get H.O. alts such as 200A+ where running at 100A's is around half max load and they'll run much cooler.

 

[dingbat]

What is the voltage coming from the alternator? Should be min. 12.8 volt, ideally 14+volts.

Do you have a voltage regulator separate from the alternator?

 

[Scott Danforth]

when down to just under 12v when running

dont run the batteries down that far. a 12 volt battery is fully charged at about 13.6 and fully discharged at about 12.4 volts (battery architecture dependent) below that, you need to slowly charge it on a 24 hour cycle. below 12 volts is severely discharged, not good for your battery, not good for your alternator. Are these flooded or AGM?

what is the voltage of your alternator output? which battery is the sense wire connected to?

you are most likely over-charging your batteries, warping the plates, creating a direct short for the alternator..... and creating a cascading failure. as the battery shorts, the voltage drops, the alternator puts out more current....eventually the magic smoke comes out.

if you are going to severely discharge the batteries, best approach is to divorce your charging/starting circuit from the house batteries. use the alternator for keeping the starting battery charged, have the house batteries charged from an on-board smart charger which is proper to the architecture of your batteries. your alternator and batteries will last longer

 

[grewvin1]

Thanks for the input good info, have installed a smart charger re-ran correct gauge wire from panel to bat's and engines. Had certified electrical marine mech do the job. Will isolate house after night sitting and switch to running bat's when at port put house on smart charger as we are usually never a day away from shore power on the Trent Severn system.