DC to DC Charger

The 60 amp DC to DC charger is fine and will not stress your new alternator. The only
difference between a 20 amp, 30, amp, 40 amp and 60 amp DC to DC charger is how
much power it pulls from the vehicle’s alternator and electrical system, and how fast it
will recharge the “house” batteries. A 20 amp charger pulls fewer amps from the
vehicle alternator but takes 3 times longer than a 60 amp charger to recharge the

Your original alternator is 180 amps and it probably has about 80 amps spare
capacity. You’ve upgraded to a 220 amp alternator which raises the spare capacity to
120 amps. A 60 amp DC to DC charger will only use about 1/2 of the spare capacity so
you should be very safe.

The DC to DC charger has nothing to do with the number of solar panels you
have. Like a plug-in 120 volt charger, it’s rating only effects how much power is drawn
from the power source (wall socket or vehicle alternator), and how fast it will charge the

Also remember that with your “house” batteries you’re not going to be loading the the
vehicle batteries, alternator or electrical system with anything but the Battery to Battery
charger and that’s only when the vehicle is running and the B to B charger senses that
your house batteries are low. Even then it will only pull a maximum of 60 amps from the
vehicle electrical system. Your inverter, cabin lights, USB chargers, fans, refrigerator,
and other appliances will be running directly off the house batteries. The vehicle
starting battery and electrical system will not be affected at all.

Solar Controller

Unlike the DC to DC charger, the solar controller should be closely matched to the
number of watts your solar panels can produce. Solar panels are not 100% efficient. A
300 watt panel will be doing well to produce 250 watts under real world conditions when
it is in hot sun on a clear summer day. So let’s say you have three, 300 watt solar
panels. These will produce about 750 - 775 usable watts. This translates into about 65
amps maximum going to charge the batteries if everything is perfect.

What is “Perfect”
Perfect solar conditions is when the solar panels are perfectly clean, the sun is exactly
90 degrees to the panel both up/down and left/right, and the there are no clouds, dust,
smog, or anything else in the atmosphere to to reduce the intensity of the sun, and the
panel itself is 70 degrees F or cooler. Even with everything aligned perfectly, the sun
moves across the sky so the exact 90 degree condition only lasts for a matter of
minutes unless you have a tracking system which just isn’t going to happen on a
van. The sun will heat the black panels to way above 70F very quickly so you loose
power there as well. Finally, when was the last time you saw a perfect summer day with
no smog, clouds, or dust? - and are you really going to wash your solar panels every
morning? What all this means is, that 99% of the time your 900 watt system will be
putting out much less than the maximum 65 amps.

Since things are seldom perfect a 60 amp MPPT solar controller would work perfectly
for a 900 watt system. On cool very sunny days with the sun directly overhead you
might loose a couple of amps in the system, but for systems up to 900 watts, I don’t
think it’s worth the extra cost to go with an 80 amp controller. The small percentage of
time (probably less than 2%) that the system could actually produce and use the extra
couple of amps just isn’t worth the expense of a higher amperage controller.

If your system is 1,000 to 1,200 watts, then I’d move up to an 80 amp solar
controller. My system is just under 900 watts and I use a 60 amp controller. For 600
watt systems I recommend a minimum of a 40 amp controller, though Victron makes a
very nice 50 amp controller for a reasonable cost which would be perfect for a 600 watt
system as well. Just make sure that whatever solar controller you purchase, it is an
MPPT controller.

None of the above is critical. The general idea is that you use a DC to DC charger that
won’t stress the vehicle electrical system but will provide enough amps to charge the
batteries in a reasonable time.

You choose a solar controller that is large enough to use 99% of the solar power
generated by your solar panels under normal good solar conditions. you don’t want to
use a 40 amp controller for a system that will produce 60 amps on a good sunny
day. You’d be wasting 20 amps which is equivalent to one 300 watt panel. We don’t
want to waste that much power.

With all this in mind, you can use any brand of B to B charger you want. Sterling makes
a 30 amp and a 60 amp DC to DC charger. Renogy makes a 20 amp and 60 amp DC to
DC charger. Any of these will work as long as they have either a pre-programmed
setting for Lithium or a Custom setting that can be programmed for Lithium. The
amperage rating will only determine how long it will take to re-charge your
batteries. Even with a 180 amp alternator your alternator and vehicle electrical system
would be fine for anything up to 60 amps.

You can use any brand MPPT solar controller you want as long as the input voltage can
handle a minimum of 100 volts from the solar panels and the amperage rating will
handle the amount of power your solar panels will produce - a minimum of 40 amps for
a 600 watt system, a minimum of 60 amps for a 900 watt system, and 80 amps for a
1000 to 1200 watt system. Victron, Renogy, and Morningstar all make good
controllers. I can’t recommend Outback as a friend of mine has an Outback solar
controller and he tells me that it will stop charging occasionally for no reason and he has
to do a manual reset on it to get it working again. Outback has not ben able to resolve
the problem. Again, make sure the controller you purchase is an MPPT controller and
that it has a program for charging Lithium batteries or has a custom setting that will
allow you to program it yourself for properly charging Lithium batteries.

There may be other brands of chargers and solar controllers that are acceptable. These are
just the names that I’m familiar with. Check out Will Prowse’s YouTube channel for more up to
date information.