gapper2 said:
My understanding of what SternWake was saying is that you DO need to fuse between the high amp side of the solenoid to the plus side of your house battery. In your original drawing you had your fuse on the other leg of the solenoid to the alternator which I believe he was saying that a fuse on that leg was not needed. I'll hope he will chime in again. I've got electronics background but no rv or solar experience.
gapper
Always fuse close to the battery, as that is the power source.
The original vehicle cable from alternator to battery is already fused, not at the alternator, but closer to the battery. So that wire is already protected.
The Additional alternator to solenoid to house battery circuit needs a fuse or circuit breaker close to house battery (+) terminal.
IF one takes power for the solenoid to house battery circuit, from Engine battery, then this circuit needs to be fused on both ends, One Close to engine battery, one close to house battery.
The alternator is a power source, but if the (+) cables are compromised, it can't make any power, so those cables need only be fused close to battery.
If you want to fuse it close to the alternator, you certainly can, but it would be a redundant fuse and one more possible failure point, and would introduce some resistance.
I recommend taking power for solenoid from alternator(+) stud rather from engine battery, as not only is the circuit most likely much $horter, but it also bypasses the 'too thin' Original vehicle wiring, which was never designed with a depleted additional battery tacked onto the end of the circuit.
When power for solenoid to house battery is taken from engine battery, the original wiring acts as an electrical bottleneck, as it was not intended to pass an additional~40 amps for an hour or more.That would cut into profits and teh C.A.F.E. fuel economy numbers. Inadequate wiring for the load it is asked to carry will heat up, become more resistive, dropping pressure and flow to the depleted house battery, increasing times to recharge, or accomplishing less recharging in the time that the engine is running.
How much juice the battery can suck, depends on the charging voltage it sees, so thick cable ensures the battery sees higher voltages, and can drink the good stuff at a higher rate.
Also there is the voltage regulation. With the fully charged engine battery in between alternator and house battery, it kind of acts like a restrictive filter. The voltage regulator has a harder time 'seeing' the depleted house battery on the other end of the circuit, and perhaps decides that it is safer to drop pressure (voltage) to 13.7v, at which point much less amperage flows.
This 13.7v reversion( premature float voltage) will likely happen anyway, sooner than desirable, and how much of a difference this ultimately makes is highly vehicle dependent.
HOwever, with the depleted house battery sucking juice directly from the alternator on its own circuit, there remains a higher chance that the voltage regulator, whether it be internal to the alternator, or an external unit on the firewall, or internal to the engine computer, might see that it requires higher field current to maintain system voltage at 14.4 +/-, and allow 14.4v to be held for longer,
Making driving to recharge significantly more effective than if 13.7v were all that was allowed or occurred too soon.
The premature 13.7v reversion is the enemy of a depleted house battery, and is kind of inevitable, unless of course one decides to upgrade or bypass the original vehicle voltage regulator, and all that that entails.
The only time I would recommend taking power from engine battery instead of alternator, is if the hoouse battery is located in engine compartment, or the back of the alternator (+) stud is just so incredibly difficult to reach that it is not worth the effort to stack another ring terminal on that output stud.
Along the lines of the alternator(+) output stud, if a fuse was required here, there would be a factory fuse located on the original wiring here too. There is not.
Also if the house battery were just a single inexpensive AGM battery, these instruct the end user to limit recharging amps into a depleted battery, to 30% of the amp hour rating. So a depleted 100 AH group 27 cheapo AGM battery should not be allowed more than 30 amps, and this can be inherently limited by a longer than necessary, thinner than really desirable cabling between alternator and house battery. If this is the case, then trying to Ekk out maximum amperage into the battery via the shorter thicker more efficient circuit is not desirable, and taking power for solenoid right from engine battery instead will restrict pressure(voltage) and thus flow(amperage) into the depleted battery is also lessened.
I do think most of these lesser$$ 30% restricted AGMS can safely be fed more than 30%, but I cannot recommend not following the manufacturer recommendations.
Those that do want to feed a well depleted 30% limited AGM should monitor battery temperature during that first half hour of exceeding it. 120F is absolute maximum, but once it reaches that area it has been accellerating quickly, So I'd say limit it to 105F while high amp charging via alternator or other powerful charging source.
Also keep in mind that one will hear that a slow recharge is always best. This is true, mostly, if the battery is still healthy, and/or IF one has all the time in the world to recharge fully. If the next deep discharge cycle will begin in a few hours, a high amp recharge that helps keeps the battery from being overdepleted that night, is much less damaging than a low and slow recharge which then allows the end user to overdepleted the battery well below 50% that night.
DO not fear higher amperage recharging, just keep the lesser$$ AGMS 30% maximum amperages 'recommendations', in mind.
Also the alternator has to work harder, and the engine needs to produce1HP for every 25 amps the alternator makes. Keeping the alternator cool is wise. Idling to recharge a depleted battery, when not moving can really overheat an alternator, in about 12 to 15 minutes can be in the danger zone.
But highway driving bathes the alternator in cooler air, and the higher rpms move air through the alternators fan quicker as well.
BUt those with alternators that are 500$ and require 1000$ of labor to replace, likely would be better off limiting its workload by using thinner cabling between alternator and depleted house battery, or at least ensuring they do not idle to recharge.
How hot the alternator gets Idlingparked vs when moving is highly vehicle specific. At 65MPh I have not been able to get my alternator above 135F. When Idling at a traffic light with a depleted battery it can rise from 125 to 165f and rising fast before the light turns green. Soon as I start moving temps begine dropping again.
The higher$$ AGMS pretty much require amperages in the 30% or higher range if cycled regularly to 50% or Below, and they have no easily attainable upper amperage limits. Just limit voltage to 14.7 at 77F, adjust downward for a hotter battery.
Flooded batteries will likely use water at a faster rate when high amp recharged, but can easily accept huge recharging currents when time to recharge is limited, Like when driving A to B and back to A, or A to B is not very far, or when using a generator to power a high amp charger.
Aging flooded batteries will also increase the rate at which they use water, and part of this is that one needs to hold absorption voltage for longer and longer as they age to get them truly full. But even if absorption voltage duration is not increased, they will use water faster as the deep cycles accumulate, SO do not use the 'I only have to water them every X months" as a rule for their whole lifetime..
Also the (+) circuit is only half the circuit. If house battery is grounded to frame, then the original Engine to battery ground then has to carry the additional current. Which will become the Electrical bottle neck which will drop voltage and slow charging to some degree.
Those seeking maximum alternator contribution, would be wise to ground house battery to Alternator mounting bolt (over the same thickness cable as the (+) side of the circuit), or (-) output stud, if one exists.
Second best would be to add another ground from frame nearby alternator to Alternator (-) bolt.
Third best would be to replace and thicken the original engine battery to engine ground.
Fourth best wouldbe to add another ground from engine battery to engine, in parallel to original engine battery to engine ground.
The alternator is an Awesome charging source, for a depleted battery that can accept huge recharging currents. however, too thin wiring can limit recharging currents. Also the voltage the alternator is allowed to seek is a huge limiting factor, as a 70% charged battery might require 30 amps to be held at 14.5v, the same battery would likely only be able to accept only 9 amps if all it was allowed to seek is 13.7v.
The Alternator's voltage regulator has the ultimate say in how well a battery is recharged, and there is not really much one can do, to change its settings for better faster recharging.
but one can at least not intentionally introduce restrictions by using too thin or too long of a circuit, and putting the house battery onto the end of the engine battery, is a much much longer circuit than alternator to house battery ( through solenoid) directly.
Hope the redundancy typed above helps explain it better.
