OR avatar image
OR asked

Alternator and solar charging a service battery - which products do I need?


I am trying to figure out if and how I can achieve the same/similar setup as with a Redarc BCDC1225D or ctek D250SA (SE); i.e. I want to charge a service battery in the car with the alternator and a solar panel, potentially both providing power at the same time (solar panel on the roof while driving). Obviously, the starter and service battery should be disconnected when the engine is not running to avoid the starter battery from running flat.

I am looking at the SmartSolar MPPT 75/xx and the Orion-TR Smart DC-DC Charger. Using each standalone would not be a problem but how would I need to connect the two units and the battery together?

(Secondary question would be to install battery sensor and have battery sensitive charging).

The reason for trying to work with VE products is the Bluetooth capability which I consider very valuable and quite unique in this area.


MPPT ControllersOrion DC-DC Converters not smart
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2 Answers
spirou avatar image
spirou answered ·

You just wire any charging device in parallel. In practice you might want to use a + and - busbar to make it easier but it's still the same idea.

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OR avatar image OR commented ·

What about overcharging when two charges run their charging profiles in parallel? Or would they compensate for each other?

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spirou avatar image spirou OR commented ·

A lead battery won't accept unlimited charge no matter what the combined output of both chargers working together might be. In a way yes, they will compensate for each other. You're likely going to get most of the current from the alternator and both will taper off at whatever absorption voltage you set. I presume the orion also has adaptive/max absorption duration setting as the MPPT so that also won't be going on forever to boil a battery.

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jasonatptld avatar image jasonatptld OR commented ·
I have the same question. I've seen that it is common practice in RV, van, and boat systems that installers will use both an Orion DCDC charger to charge from the alternator and MPPT solar charger. The outputs of these devices are simply connected in parallel on the 12V/GND bus. So how is it that they are coordinating or how do we justify that they do not need to coordinate? We could extend this further in 2 regards.

1. Most of these systems also utilize an inverter/charger which would be yet another parallel charging source.

2. The documentation for the Orion DC to DC chargers state that an "unlimited" number of these chargers can be connected in parallel to increase charge current capability.

If a lithium chemistry battery does not like to be charged at more than 0.5C, and we have 3 different sources of charging current, how do we prevent the total charge current from exceeding 0.5C, if the devices are not coordinating? If each charging source was capable of 0.4C (just as a example), then 0.4+0.4+0.4 = 1.2C which would not be good for the batteries.

I skimmed through the manuals for the Orions, and the MPPTs, and Victron's wiring guide and I could not find any examples of system that utilize both in parallel, nor could I find any explanations on how an unlimited # of Orion DCDC chargers could be wired in parallel without needing to worry about charging batteries too quickly.

I would really love to understand the technical details of how these systems manage before pulling the trigger on the gear.

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kevgermany avatar image kevgermany ♦♦ jasonatptld commented ·
Victron manage total charge current across multiple devices with the DVCC facility. This is provided by a control unit such as Cerbo, Colour Control GX.
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dazey77 avatar image
dazey77 answered ·

At the most basic you charge the service battery from the MPPT and take a charge line from the starter battery/charge circuit via a smart relay (Vsr)

in Victron this means the mppt and a Cyrix battery combiner. This just connects the circuits when the engine is running. A DC-dc converter offers more controlled charging (as the ctek does).

there is a bit more too it than that but that’s the basic idea

if you read the manuals for all the components, they have example schematics that will match your requirements.

also search for the Victron ‘wiring unlimited‘ guide In google, it’s a free pdf and will help you

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spirou avatar image spirou commented ·

Cyrix or any other VSR is a cheap & simple, but terrible device that has no place in systems with smart alternators and/or modern batteries where resting voltages are over 12.8V when full.

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dazey77 avatar image dazey77 spirou commented ·

I think calling them a terrible device is somewhat ridiculous. They are cheap and simple and do what they say.

Yes they might not work with a smart alternator.

Yes they might work in a limited fashion with modern batteries (but they will still work to a degree).

I use one in an old vehicle with a lithium battery, works fine for my use, which is emergency top up in winter. Most of the year my split charge circuitry is turned off and I rely 100% on solar. In winter I can add some charge from the alternator but it won't fully charge the batteries easily. For my use, the cost of the DC-DC would be ridiculous.

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OR avatar image OR commented ·

Thank you @spirou for the insight, exactly the kind of advice I was looking for; and thank you @dazey77 for the reading advice, already downloaded the book.

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