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fddjr1 avatar image
fddjr1 asked

smartsolar 100/30 and using to charge start battery

I have a SmartSolar 100/30 MPPT charger with a 100ah deep cycle AGM battery. Separately I have the starting battery in the engine compartment that has a bit of parasitic drain and requires charging after 3-4 days without starting the engine. I was wondering if the Cytrix combiner or some other Victron component would allow for the starting battery to be charged. If there is a potential product available, would I need to at least also get an AGM start battery (now a flooded lead acid) so that the charging profile setting (option 2 I believe) would be a match for either battery? My other alternative if there is no 'integratable' Victron product is a small panel with controller for the start battery, but I would like to avoid if possible. Thanks for your time.

MPPT Controllers
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spirou avatar image spirou commented ·

The simplest solution really is a separate small, removable panel just for the starter battery. Depending on size it might not even need a controller.

I would avoid the cyrix VSR as it is a "dumb" device best suited for identical battery types. However, if resting voltage of the AGM is below 12.8V it would work. If not, the starter batt would be discharging the AGM below full. As you say, a point to consider is the charge profile which won't be ideal for the starter battery. But if you limit the current to 1-2A (as most dual solar chargers do), it won't matter too much.

Also a simple solution is a manual switch, rather than a VSR, so you can control when you want to split the charge. What you need to consider is that by using a VSR, charging would work both ways whenever one of the batteries is above certain voltage. Do you currently have a system for alternator charging of the AGM, or just the starter battery?



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Justin Cook answered ·

@fddjr1, the Cyrix-ct is a viable solution for your particular use case, with a caveat: it's bidirectional, so while you could certainly connect it between your aux batt and your start batt, and it would indeed connect the two batteries when your SCC raises the aux batt voltage to >13.3v, thus allowing your MPPT to charge the start batt at the same time, it will also connect the start batt to the aux batt when your engine is running and your start batt voltage is >13.3v, meaning that your alternator would be charging your aux batt at the same time. Given that they're different chemistries, this may or may not be an issue - it depends entirely on the charge voltage recommendations of your aux batt. Given that AGM batteries are regularly used as start batteries to begin with, I strongly suspect that your AGM will be perfectly happy being parallel-charged by your alternator, but again, it's entirely dependent on the manufacturer's recommendations.

All that being said, the simplest and cheapest solution for you would probably be a Cyrix-ct and a small toggle switch; use the toggle switch to interrupt the Cyrix's ground wire. Without a ground connection, the Cyrix will stay open (leaving the two batteries disconnected from each other). Thus, when you're parked and you just want your SCC to keep both batteries full, leave the toggle switch "on" (ground connected) and the Cyrix will close at its normal voltage thresholds, connecting the two batteries, and your SCC will keep both batteries charged. When your engine is running and if you don't want your alternator to charge your aux battery, just flip the toggle switch off, disconnecting the Cyrix ground wire, and the Cyrix will stay open with the batteries disconnected from each other.

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fddjr1 avatar image fddjr1 commented ·

@Justin Cook, thanks for getting back to me. It has been some time since I last posted about this. I do have a few follow up questions to narrow in on the product capabilities and the set up I was considering. I understand that the -ct product would be the one for an AGM house battery and the -Li-CT would be for a Li house battery. Given that the switch is bi-directional as you mentioned, if I was charging from the Alternator, then the start battery would charge where it needed to and then when the cyrix senses the voltage above 13.3v, it would connect the house battery and let the current flow to the house battery. Here are my 'ignorant questions' I wanted to confirm: a) Once the starter battery is fully charged, it will not 'accept' more charge due to resistance? b) So the additional current the alternator is putting out to run the car electronics/engine, will flow through the cyrix to the house battery and will not damage the starter battery? c) If the house battery is a Li based and it has an integrated BMS, the Li battery will regulate itself to charge with the current coming from the cyrix-li-ct? and d) If you wouldn't mind taking a look at the modified wiring diagram I took from the cyrix-li-ct manual, can you let me know if I'm thinking about the wiring to the ultimate house-based charging devices? I added pictures for the solar panel and SCC and then some text boxes (highlighted in yellow) for the downstream house-based charging devices. I know it's a little off topic to the cyrix, but I am trying to make sure that the system will work for what I'm intending. Goal is the the SCC can provide ongoing power to fridge/freezer and other electronics and charge the house battery and the starter battery (for parasitic drain) if the van is parked for long period of time. As you indicated, if the cyrix-li-ct is 'connected' with the toggle switch, then the alternator will charge both the starter battery and the house battery, which could be done if I could not get the solar panels deployed enough to keep the house battery charged. Thanks so much for your time.

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fddjr1 answered ·

@Justin Cook. Thanks for the response. I think I understand what you're explaining. In looking at the suggested wiring diagrams in the Cyrix-ct manual, it seems that the sample charging source is a Multiplus that would allow charging from the alternator or a shore power source. What you're saying is that the Cyrix doesn't really care about the source of the current (solar vs alternator) and instead just opens and closes based on the volatage so I could use in combination with a switch to manually force it to charge across similar AGM batteries. I ended up returing my flooded starter battery and got an Odyssey Exrtreme AGM, so that takes care of the charging profile not being available on the SCC.

On a related question but now if I was thinking I would use a lithium house battery, I see that there is a Cyrix 'Li-ct model that allows for charging between a lead acid starter battery and a lithium house battery (similar to the ct model for lead acid batts only) and was wondering if your suggested solution (with the Cyrix Li-ct) would still be functional or if I would remove the switch and the Cyrix would handle the different voltages.

Final question based on the diagrams I'm seeing for either the Cyrix ct or the Li-ct models is that there is a VEBus BMS being connected to the Cyrix and the Multiplus. If I don't have the Multiplus and only the SCC, do I need to get the BMS for any reason?

Curious for your thoughts. Thanks again!

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Justin Cook avatar image
Justin Cook answered ·

@fddjr1, the switch is actually to force disconnection, not connection - connection is automatic based on voltage, so the switch is only necessary to force disconnection in the event that you do not want the batteries connected when the voltage trigger point has been released.

As for the Cyrix-Li-Ct: yes, when using an LFP house battery you should use the -li- version; this is functionally identical to the normal Ct except that the voltage trigger has been raised from 13.3v to 13.6v to account for the higher resting voltage of the LFP battery.

So long as the LFP battery you'll be using for your house battery is a drop-in (meaning, it has an internal BMS) such as a Victron SuperPack, a Battle Born, or any number of other drop-ins that are readily available, then you do not need an external BMS and can connect the Cyrix-Li-Ct in a normal configuration. If your LFP battery is not a drop-in, then it definitely requires a BMS, irrespective of the Cyrix.

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fddjr1 avatar image fddjr1 commented ·

@Justin Cook, thanks for getting back to me. It has been some time since I last posted about this. I do have a few follow up questions to narrow in on the product capabilities and the set up I was considering. I understand that the -ct product would be the one for an AGM house battery and the -Li-CT would be for a Li house battery. Given that the switch is bi-directional as you mentioned, if I was charging from the Alternator, then the start battery would charge where it needed to and then when the cyrix senses the voltage above 13.3v, it would connect the house battery and let the current flow to the house battery. Here are my 'ignorant questions' I wanted to confirm: a) Once the starter battery is fully charged, it will not 'accept' more charge due to resistance? b) So the additional current the alternator is putting out to run the car electronics/engine, will flow through the cyrix to the house battery and will not damage the starter battery? c) If the house battery is a Li based and it has an integrated BMS, the Li battery will regulate itself to charge with the current coming from the cyrix-li-ct? and d) If you wouldn't mind taking a look at the modified wiring diagram I took from the cyrix-li-ct manual, can you let me know if I'm thinking about the wiring to the ultimate house-based charging devices? I added pictures for the solar panel and SCC and then some text boxes (highlighted in yellow) for the downstream house-based charging devices. I know it's a little off topic to the cyrix, but I am trying to make sure that the system will work for what I'm intending. Goal is the the SCC can provide ongoing power to fridge/freezer and other electronics and charge the house battery and the starter battery (for parasitic drain) if the van is parked for long period of time. As you indicated, if the cyrix-li-ct is 'connected' with the toggle switch, then the alternator will charge both the starter battery and the house battery, which could be done if I could not get the solar panels deployed enough to keep the house battery charged. Thanks so much for your time.

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