Quick mod to maintain engine battery from solar supply

Yes, but I would have to run a new wire from the house to the engine compartment to reach the engine side of the relay or the battery itself.

My next little project is to make a step down alarm that rings when I start the engine with the step down. I am thinking of a magnetic switch on the step that switches off when the step is up. I have an easy route for wires from the switch into the house and hopefully can get from there to an engine on live fuse in the inside fuse box.

Hi Harvey51,

The wires are still there--so you could splice into them.

Harvey51 wrote:

Pianatuna wrote:
There is no need to run an additional wire. My trik-l-start resides beside one of the (LARGE) isolation relays and simply connects the house battery side to the engine side.

Ah clever! But my battery isolator is in the engine fuse box.

Pianatuna wrote:
There is no need to run an additional wire. My trik-l-start resides beside one of the (LARGE) isolation relays and simply connects the house battery side to the engine side.

Ah clever! But my battery isolator is in the engine fuse box.

There are several Blue Sky Energy solar controllers with a 2 amp auxillary battery charging connection.

Hi Harvey,

There is no need to run an additional wire. My trik-l-start resides beside one of the (LARGE) isolation relays and simply connects the house battery side to the engine side.

I also added manual control to the solenoid(s) (I have two circuits for charging), so I can "shut it down" to avoid overloading the alternator. Duty cycle is 1:3 so on my 130 amp I don't want to go much above 42 amps for very long. My solenoids are rated for 100 amps continuous -- the OEM Ford unit lasted less than one year. I replaced the 60 amp fuse with a 50 amp automatic circuit breaker.

Harvey51 wrote:
Thanks, Treeseeker. I was thinking of an ordinary maintainer but see Trik-L-Start is special. I appreciate the advantage of Trik-L-Start over my piece of wire in preventing discharge of the engine battery into the house and independently regulating its charging.

The idea of running a new wire from house to engine is not welcome at this time, though.

Thanks, Treeseeker. I was thinking of an ordinary maintainer but see Trik-L-Start is special. I appreciate the advantage of Trik-L-Start over my piece of wire in preventing discharge of the engine battery into the house and independently regulating its charging.

The idea of running a new wire from house to engine is not welcome at this time, though.

That's interesting, but the relay in my C that connects chassis to house 12 systems is not in that box. It is a lot bigger, more like a starter relay.

I have that relay slot in my passenger van, but no relay in the slot, because it doesn't have the towing package.

Use of the towed vehicle charge circuit to charge motorhome house supply is kind of neat, intersting that one manufacturer uses it, but for many C motorhomes the power draw will exceed the ratings of that circuit.

Harvey51,

I think you may have not understood Pianotuna's comment about using a Trik-L-Start. This is not a traditional 120VAC trickle charger but rather a device that connects between the house battery and engine battery that keeps the engine battery charged while the house battery is being charged (by another source).

For more about the Trik-L-Start see here.

The problem remains that the ECU "sees" the starter battery and limits charging according to that state of charge.

My 2nd circuit connects directly to the starter battery and I hope "drags it down" to force the ecu into action.

The only sure fire way to get more charging with a single alternator is to use an external diode on the alternator. Then it behaves independent of the starter battery.

So far I have not needed to do this.

Interesting, as are all your posts! Your system is a full order of magnitude bigger than mine, which has a 100 watt solar panel and the greatest engine charging of my 2 house batteries I have observed is 6 amps.

I don't think there is a larger relay. I spent a fair bit of time looking for the kind of selenoid or solid state disconnect that people with larger motorhomes have posted pictures of. Just now, I went looking for the .88 amps you mentioned. I connected the engine battery through a multimeter set on its 10A range and put another multimeter on 10A in place of the jumper wire. I observed about 0.4 A coming in from the house on the jumper meter and 0.35 charging the battery. With no current coming from the house, about 0.05 A flows out of the battery, which must be the parasitic current of the vehicle. With a door open and courtesy light on, an extra amp came in from the house solar system and didn't go into the battery.

The relay I replaced with a jumper is called the "Trailer battery charge relay" (E). There is a 40 A fuse also named "trailer battery charge relay" (8).

No current rating is given for the relay in the book or on the relay itself, otherwise so well self-documented. However, I happen to have a spare one still in its package that is rated at 40 Amps.

I find it interesting that the system is set up for 40 Amps but only achieves 6 A of battery charging. Maybe I could benefit greatly from one of those DC to DC voltage changers.

I like my little jumper better than a trickle charger. Such an efficient simple solution. No converting DC to AC and back again; only 4 inches of wire! I accidently made it just long enough to work with my clampmeter.

What the heck is the "auxiliary battery relay" (fuse 20 in the photo) for?