Can this deep cycle battery be charged by an alternator?
- Thread starter nat
- Start date
Crom
Expo this, expo that, exp
Yes you can do that. Any sized wire will be sufficient to charge the battery. But skinnier wires will take longer to charge the battery. For reference my truck has a 10A max on the cig lighter outlet, it will definitely work as a charging source but I'll be limited to 10A per hour charging through it. To give you an example, if your 100 Amp Hour battery is discharged to 50% It would take roughly 5-6 hours to bring it back up to 100% charging at that rate. And honestly, not to get too complex, but with an alternator your battery will probably never reach 100% charge. If I wanted to build a dedicated aux charging port in my vehicle I'd use wire capable of delivering 30 Amps of current. You can use this as a tool, but you need to know some basics about the wire you're planning on using: http://circuitwizard.bluesea.com/
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I would tend to disagree, one of two things is going to happen:
1) The small factory wires will cause too much voltage drop to actually charge anything. This is most likely going to be the case.
2) If the wires manage to not drop the voltage too much then you'd likely blow the fuse as there would be nothing to limit the battery from trying to pull more amps if it was discharged.
So put in some decent sized wiring and fuse appropriately.
Crom
Expo this, expo that, exp
Voltage drop is a function of load and length of the conductor. And with 10 amps that's not a very big load at all, and we're presuming the distance is't outrageous. Skinny wires work. Look at battery tenders and smart charges, they got pretty skinny wires and even at 4-7 amps they will happily charge a battery. As long as the voltage of the charging bus is higher than the battery voltage it's gonna work. It will just take a while.
If anybody out there wants to avoid guessing use this nifty tool to size the wire correctly: http://circuitwizard.bluesea.com/ Not hard to do.
8 AWG would be just fine for a dedicated charging port. You could safely do up to 30 Amps @ 15' with a voltage drop of 5% under full load with wire rated for 60° C.
Definitely going to be better than the likely 16 or 14 gauge in your cig plug. You'll still need a solenoid or relay to connect/disconnect when the vehicle is on.
Assuming a 2% voltage loss still has a decent enough voltage for charging and you have 15' of distance from your main battery to the aux you'd be looking at 12amps with that wire gauge (feel free to adjust parameters as you see fit). A 40 amp fuse and 40amp relay (or 30amp fuse with 30amp relay depending on what you buy) might be the easiest for that size wiring for ya. Jump to a solenoid and beefier wire if you want more out of the system. The battery isolator thread goes over that well.
Voltage drop is a function of load and length of the conductor. And with 10 amps that's not a very big load at all, and we're presuming the distance is't outrageous. Skinny wires work. Look at battery tenders and smart charges, they got pretty skinny wires and even at 4-7 amps they will happily charge a battery. As long as the voltage of the charging bus is higher than the battery voltage it's gonna work. It will just take a while.
If anybody out there wants to avoid guessing use this nifty tool to size the wire correctly: http://circuitwizard.bluesea.com/ Not hard to do.
8 AWG would be just fine for a dedicated charging port. You could safely do up to 30 Amps @ 15' with a voltage drop of 5% under full load with wire rated for 60° C.
He mentioned back of the truck, I'm assuming that will be about a 15' run of wiring by the time it gets there from the battery. I'm guessing his cig plug is likely 14ga at best, its not going to provide worthwhile charging, esp. if he's got a bunch of 8ga wire already. Spend $10 on an inline fuse holder and 40amp relay and do something decent.
I would say 5% drop is too much for charging. Say your alt is putting out 14.4V at a 5% drop you'd be down to 13.7V, that is typically a float voltage, that isn't going to push 30amps into a battery.
Crom
Expo this, expo that, exp
I may have missed his comment about in the back of the truck...I'm with you and I agree to use the 8 AWG. That's what I would do.
Most of what I wrote was to show that it was indeed possible with the factory wiring. In now way did I intend to convey that it was optimal.
To continue the discussion about charging... It turns out I ran the Blue Sea circuit wizard again with the same parameters as before but stated an allowable voltage drop of 3% and it sill recommended 8 AWG for the charging circuit in this application. However, a deeply discharged battery will draw more current initially, but as the voltage begins to rise and the battery becomes charged it will draw less and less current because of the battery's internal resistance. The point in writing this is that, as stated the voltage drop is a function of current and the resistance of length of the conductor. Well the 15' length of wire is static, but the current is not; it's variable. To put this another way, as the battery becomes charged there will be less and less voltage drop, maybe a couple hundredths of a volt difference. dwh recently wrote on this subject in his post here.
Also, if your alternator is putting out 14.4, I'd consider that to be very very lucky! Mine only ever does 14.11 at best.
I was trying to be generous on the 14.4V (my old truck actually did up around there though, I haven't checked my new one) so as not to take the worst of everything but I agree lots are down lower. I will not argue that you'll get "some" charging off the factory system but it would be pretty weak so I'm just taking the stance of not being advisable. Too often people kill off their batteries by under charging them, spend a couple dollars now and keep those batteries happy! Generally sounds like we're all on the same page now.
dwh
Tail-End Charlie
Depends - it might not.
A battery that's very deeply discharged, i.e,. dead, will also have a very high resistance and won't draw much at first. After it charges up some the resistance will drop and then it'll draw more until it gets close to full when the resistance rises again and the current flow drops off.
Yea, exactly.
I think it's easy to overlook that voltage drop as regards feeding a load from a battery behaves differently than voltage drop as regards charging a battery.
For instance supplying a 1200w load from a 12v battery would give you 100a current flow and X voltage drop. However, as the battery voltage drops down, the amperage flowing goes up to supply the same 1200w. If the battery gets down to 10.5v, the amp flow would be closer to 115a. So when figuring voltage drop for LOADS you would need to use the worse case numbers. You'd need to plug 10.5v, 115a into the voltage drop calculator to find out what size wire you really need to supply that 1200w load.
In other words, with LOADS, over time, the amperage flow FROM the battery increases, and so does the voltage drop.
But it's the OPPOSITE effect when CHARGING a battery. When charging, over time, the amp flow decreases, and so does the voltage drop. By the time the battery has reached a surface charge equal to the bus voltage, there isn't enough voltage drop to notice.
And even if there is theoretically a voltage drop, what effect would it have on charging? None really.
Let's say the battery is at 11.5v. That will hold the bus voltage down to 11.5v. The voltage regulator will see that and switch on the alternator and keep it on till the bus voltage reaches whatever the set point is (14.4v or 14.11v or whatever).
But the bus voltage won't reach that point until the battery surface charge reaches that point.
As long as the alternator is turned on, the POTENTIAL voltage of the bus is going to be higher than the actual voltage of the battery (thus negating the effect of a voltage drop), until the battery surface charge reaches equality with the bus voltage, and then there isn't any voltage drop anyway.
A smaller wire can make it take longer for the battery to reach a surface charge equal to the bus voltage, but that's about it.
And from that point on, it's just a trickle/absorb effect until the battery chemistry is finally fully activated.
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dwh
Tail-End Charlie
Oh, and to answer the OP's question:
Any lead-acid battery can be charged by an alternator. GEL types are sensitive and most recommend not exceeding 14.2v. If your truck's voltage regulator is set to 14.4v, then you could overcharge a GEL.
But that battery in the pic is not a GEL. It says down at the lower left that it can handle 14.4v-14.8v cyclic charging (i.e., alternator/voltage regulator), so no worries about it being overcharged by any normal 12v automotive charging system. In fact, it'll likely never reach 100% charged.
Any lead-acid battery can be charged by an alternator. GEL types are sensitive and most recommend not exceeding 14.2v. If your truck's voltage regulator is set to 14.4v, then you could overcharge a GEL.
But that battery in the pic is not a GEL. It says down at the lower left that it can handle 14.4v-14.8v cyclic charging (i.e., alternator/voltage regulator), so no worries about it being overcharged by any normal 12v automotive charging system. In fact, it'll likely never reach 100% charged.
4x4junkie
Explorer
Must depend on the battery... One time I had mine (Delco Voyager flooded) discharged somewhere down around 9-10 volts (yea I know that's bad, it was unintentional). When I first connected a 10-amp charger to it (older manual-style charger), it pulled so much current it caused the charger to go into overload and shut off (it's meter immediately pegged with a *clink* sound for about 15 seconds before the internal breaker cut out). I had to charge it through a headlamp bulb (used as a resistor) put in series with the charger's lead for about an hour before the battery had enough surface voltage to not kick the charger off when connected straight to it.
Just an observation I made with mine.