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Discussion Starter #1 (Edited)
Came across this on the Transit forum, Votronic 2A 12V DC to DC battery.
This caught my attention, as I run an extension cord for a battery maintainer. Since I have a solar setup I should get it to maintain the starter battery when the van sits.

One of the reviews mentioned it's just a current limiting resistor and a diode. Being cheap I figured for $5 I could get (for example) a 4 ohm 50 watt resistor, diode and a switch. I still need to run some numbers and think it through.

Feels like I'm missing something :)
 

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Most maintainers these days have settings for battery type and overcharge protection. In my experience (20 years leaving several vehicles for 6 months) I will say an always-on maintainer of this type is likely to ruin a battery. I run mine a week/month or on an hour/day with a timer. Since beginning that, I have never lost a maintained battery. I’d be leary of something that simple in these days of smart electronics. Those who know me will be falling down in disbelief I would say such as thing but it is true.
Our van batteries do need something like this to be left for a month or more and a smart charger that has voltage control and perhaps a timed charge circuit would be a great addition and I would buy one at a $50 price point.
 

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Discussion Starter #3
If my setup works the way I think it will, the solar charge controller will maintain all batteries if necessary. I only want a small amount of amps going to the starter battery and the diode will prevent the starting battery from charging the coach batteries.
 

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So, you want to connect the starter battery to the house battery bank and have the solar keep all the batteries topped off, but put a diode between the house and starter to keep the starter from feeding back into the house.
I think I get the concept.
But, if the house and starter are different types of batteries, how will the charge controller know to charge them differently?
I'm thinking it might be better to do what RD said and let the solar maintain the house and put a maintainer on the starter.
Or can you setup the charge controller to charge 2 separate battery types with separate charge parameters, simultaneously?
 

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Two amps seems a bit skimpy if you have any significant parasitic loads. A diode means your coach battery will never be 0.7V less than your house batteries, so if you want to maintain 13.76V on the coach battery your house batteries will need to be at least 14.46V. The charge rate will be very low, as it will asymptotically approach zero as the charge increases.
Depending upon your house battery chemistry, a voltage operated relay (closes when any battery is above 13.6V) may be a better solution.
 

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Look at the automatic battery float charger at Harbor Freight for about $5. I have used this for my Ram MH for 3 years and no problems. The house batteries (AGM) are kept charged separate by solar panels and converter.

MLogan
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Smyrna, TN
 

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Discussion Starter #7
So, you want to connect the starter battery to the house battery bank and have the solar keep all the batteries topped off, but put a diode between the house and starter to keep the starter from feeding back into the house.
That's the goal, a one-way route to keep the battery topped off, and protect it. Not for bulk charging.
Two amps seems a bit skimpy if you have any significant parasitic loads.
The starter battery is only used to start the van, self discharge rate is avg .038v per day.
A diode means your coach battery will never be 0.7V less than your house batteries, so if you want to maintain 13.76V on the coach battery your house batteries will need to be at least 14.46V.
Mixing terminology? Did you mean the starter battery will be .7v less than the house batteries with the diode installed?
 

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Discussion Starter #8
Why don't I buy the Trik-L-Start? Because if I can accomplish the same thing for $5 I'll spend the $5 bucks before I spend $70.
 

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That's the goal, a one-way route to keep the battery topped off, and protect it. Not for bulk charging.

The starter battery is only used to start the van, self discharge rate is avg .038v per day.

Mixing terminology? Did you mean the starter battery will be .7v less than the house batteries with the diode installed?
Yes, you will always have a 0.7V drop across a diode (assuming a standard silicon diode, which most diode isolators use - I have yet to see an isolator use a Schottky or germanium diode). So if you are feeding your solar into the house batteries, then through the diode to the starter, if your house batteries are being maintained at 13.8V, your starter battery will never be higher than 13.1V.
 

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Came across this on the Transit forum, Votronic 2A 12V DC to DC battery.
This caught my attention, as I run an extension cord for a battery maintainer. Since I have a solar setup I should get it to maintain the starter battery when the van sits.

One of the reviews mentioned it's just a current limiting resistor and a diode. Being cheap I figured for $5 I could get (for example) a 4 ohm 50 watt resistor, diode and a switch. I still need to run some numbers and think it through.

Feels like I'm missing something :)
Hey Phil

If I had solar, with my ”honking manual switch” I get teased about on here, I could charge my starter or my house, or both (I can also plug in to shore power & work the same combos from my onboard charger)

My 4 way switch was $8 more than the 2 way - no brainer 4 even me

I think this is detailed in my build thread, but if not and this interests you I will post a diagram 👍🤓
 
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