diy solar

diy solar

Adding DC-DC charger to 12V system, Can my alternator handle it?

Yes, I have since found an explanation. At high rpm, the alternator generates more heat due to it's ~50% efficiency. More heat means it needs more fans for cooling, adding more load to the alternator to power the fans.
I'm skeptical.
When the alternator runs at higher rpm it can cool itself more effectively.
 
Last edited:
Also, higher RPM's usually indicate the vehicle is running down the road with more air flow through the engine compartment and lower ambient temps for the alternator.
 
I'm skeptical.
When the alternator runs at higher rpm it can cool itself more efficiently.
Also, higher RPM's usually indicate the vehicle is running down the road with more air flow through the engine compartment and lower ambient temps for the alternator.
I wish I could delete my comment because you're right, the alternator cools itself more efficiently. I made the mistake of thinking the alternator was now running the radiator fan for cooling itself at higher rpm, but the fan is built into the alternator. What is the explanation for Mike's question then?
 
A 2004 Ford would still be using the 3G alternator which normally come in 95 or 130 amp flavors depending on if they have a small or large case. Are you sure it's a 115 amp unit? The small case 95 amp units have 4 holes in the small section whereas the large 130 amp cases have two.

115_1530.jpg
 
A 2004 Ford would still be using the 3G alternator which normally come in 95 or 130 amp flavors depending on if they have a small or large case. Are you sure it's a 115 amp unit? The small case 95 amp units have 4 holes in the small section whereas the large 130 amp cases have two.

115_1530.jpg
Mine has the 2 holes! Are you sure this is a definitive indication of amperage rating?
 
My quick auto parts search found only 95 and 130 amps. Not sure if the oem was 115 but the 130 seems available if the 115 does not hold up.
Get the lifetime warranty ;)
 
I'm going with a 115A, shop manual says so, but thanks camel for that info to verify further. I'm not going to upgrade my alternator to a higher amperage capacity. A manual on/off switch will allow me to turn off the DC-DC charger when running high current loads like the A/C compressor. I just have to be mindful.

Looking at DC-DC chargers. Since I've settled on the Victron 100/30 smartsolar mppt for my SCC, I'm leaning towards one of the Victron Orion-Tr Smart DC-DC chargers for quality and ease of integration into the same BT app. I'm looking at the 12/12-30 non-isolated. Questions:
  • Since starter battery is already grounded to chassis and I plan to ground my house battery to chassis, the non-isolated charger is what I need correct? Not the isolated?
  • Can I program the output amperage to less than 30A if I want?
  • Does remote on/off also mean I can switch the unit off with my phone's BT app? (This relates to whether I will install a on/off switch for the DC-DC charger in my wiring. If I can turn it off with my phone I was thinking I might not need a manual switch.)
The Big 3 upgrade was mentioned in my other thread. smooth Joey said:
Another thing to consider is the "big three" upgrade.

1: engine to frame
2: frame to battery
3: battery to alternator

camelCase said:
Plus one on doing a "big three upgrade." Put a fuse on the alternator to battery wire if you do it. Highly recommended if you use the frame as a grounding point anywhere in your system with alternator charging and it helps keep voltage drops to a minimum so actual amps drawn from the alternator for the amount of current are less.

Please explain this further. I don't understand. You're saying put a fuse on the wire going from my alternator to my starter battery? Isn't my starter battery already grounded to my frame? Engine to frame? Still noob status over here.
 
All cars have some sort of over current protection on the wire coming from the alternator. On most American cars, at least until fairly recently, this was in the form of a "fusible link" which was a wire that was designed to burn out first and protect the rest of the system. Most modern cars tend to do it with a fuse, I think.

With the big three upgrade, you are overlaying the existing wiring with additional heavy gauge wire to reduce resistance and voltage drop. Since you are adding another higher capacity wire coming from the alternator you must add over current protection on that wire sized no larger than the current carrying capacity of the wire. An AMG/Mega or ANL fuse is commonly used in this application.

For example, if you are adding a 4 gauge wire from the back of an alternator, you would use a maximum of a 150 amp fuse.
 
With the big three upgrade, you are overlaying the existing wiring with additional heavy gauge wire to reduce resistance and voltage drop.
The overlay bit bugs me.
My preference is to replace the cheap legacy bits with oversized new bits.
I would pay special attention to the joinery.
@dudedogvan how long will the wire be in feet from the starter battery to the house system busbars?
Is there a good spot to bond to the chassis where the new system is going?
Have I made you a diagram yet?
 
how long will the wire be in feet from the starter battery to the house system busbars?
~14-15 ft.
Is there a good spot to bond to the chassis where the new system is going?
I should be able to find a spot
Have I made you a diagram yet?
No. I was trying to figure out specifics on these last couple main components, then try my hand at drawing up a wiring diagram for y'all to critique. You did suggest in previous posts to maybe try a diagram first with basic figures, then the forum could suggest components. Then I went down the whole alternator rabbit hole and trying to find an amp clamp and all that. Do you want to draw up a diagram?
 
~14-15 ft.
30 feet round trip
25 amps
12.8 volts
According to this https://baymarinesupply.com/calculator
6 awg will give you less than 3% voltage drop.
I should be able to find a spot
Although copper is a better conductor than steel the sheer amount of steel may be the better conductor.
I suggest to try using the chassis as the return path.
Which also makes your system voltage referenced to the chassis.
No. I was trying to figure out specifics on these last couple main components, then try my hand at drawing up a wiring diagram for y'all to critique. You did suggest in previous posts to maybe try a diagram first with basic figures, then the forum could suggest components. Then I went down the whole alternator rabbit hole and trying to find an amp clamp and all that. Do you want to draw up a diagram?
When we get a generic list of components I will make a diagram.
Not really a diagram but textual representation of the system.
Here is an example for another system.
Code:
legend {
    {} { functional block }
    nnn|NNN| { busbar fused position where nnn is wire guage and NNN is fuse rating in amps
    nnn|UUU| { busbar un-fused position where nnn is wire guage
    <-> { bi-directional current flow }
    -> { uni-directional current flow }
    <- { uni-directional current flow }
    @ { back reference }
    dpst_switch { double pole single throw switch }
}
main {
    busbars {
        positive {
            002|UUU|<->200A_fuse<->battery
            006|100|<-dc2dc_charger<-100A_breaker<-starter_batttery
            010|030|<-scc<-dpst<-panels
            002|200|->inverter
            006|100|->fuse_block
            016|001|->shunt.positive
        }
        negative {
            002|UUU|<->shunt<->battery
            010|UUU|->scc->dpst->panels
            002|UUU|<-inverter
            006|UUU|<-fuse_block
            006|UUU|<->chassis_bond
        }
    }
}
 
Last edited:
I realise this thread is quite old already, but thought I'd briefly report back after a full season with the Renogy 40A unit, including a 5500Km trip from Edmonton to northern California and back.

Most of the time I had solar power to keep the house battery charged, but as I got into low-sun situations I ran the DC-DC when highway driving. Some days it charged at 40 amps for a few hours with no apparent problems. The alternator felt quite hot to the touch, but then again, it always does. I intend to measure the actual temperature next time out in the spring.

I was careful to only charge when at cruising speed and switched the unit off when in slow traffic or idling. At 25% of 160A rated capacity I think the alternator handles the extra load well, even though the charger draws 48-ish amps to supply 42-43 to the house battery (owing to a long wire run and voltage drop).

Switching on and off from the truck cab is easy with the remote switch I installed. Shall post a "show and tell" when I have time.
 
was careful to only charge when at cruising speed and switched the unit off when in slow traffic or idling. At 25% of 160A rated capacity I think the alternator handles the extra load well, even though the charger draws 48-ish amps to supply 42-43 to the house battery (owing to a long wire run and voltage drop).
Realistically an alternator puts out less amps at lower rpm. Since all your loads are under the output rating of the alternator, just like a discharged starting battery the load presented may exceed the output at lower RPM but I believe you’d be fine in use.
Using the switch assures no problem and for sure you wouldn’t want to idle extensively at a 100A draw in your RV-type setup as eventually the vehicle battery would deplete. However, with much experience with trailer winches at a dealer and recreational off-roading, etc., if it were a major problem all the folks in my local jeep club would be frying alternators on a regular basis with the frequency of extended 300A recovery winch usage.
 
Realistically an alternator puts out less amps at lower rpm. Since all your loads are under the output rating of the alternator, just like a discharged starting battery the load presented may exceed the output at lower RPM but I believe you’d be fine in use.
Using the switch assures no problem and for sure you wouldn’t want to idle extensively at a 100A draw in your RV-type setup as eventually the vehicle battery would deplete. However, with much experience with trailer winches at a dealer and recreational off-roading, etc., if it were a major problem all the folks in my local jeep club would be frying alternators on a regular basis with the frequency of extended 300A recovery winch
Yes, I was deliberately conservative about ratings and loads. Good point you make about depleting the vehicle battery; something I was less focused on.
 
I realise this thread is quite old already, but thought I'd briefly report back after a full season with the Renogy 40A unit, including a 5500Km trip from Edmonton to northern California and back.
Glad to read the trip report was successful. I still would have recommended the 20 amp and not have to worry about the conditions.
 
Glad to read the trip report was successful. I still would have recommended the 20 amp and not have to worry about the conditions.
Yes, I did consider that option but estimated there was enough alternator "headroom" for the extra 20A (which I can really use at times). When I resume towing in the Spring, I'll either install a thermocouple on the alternator with a readout or check with a non-contact thermometer immediately after charging. That way I can use the remote control to halve the current if it appears too hot and stick with 20A.

What is the maximum surface temperature we should see on a standard vehicle alternator? Anyone have a reliable reference on that?
 
Last edited:
Back
Top