Question about mains charger and VSR

[tymonk]

Hello. I am looking for some advice.

I have a 70Ah AGM starter battery and a 80Ah AGM domestic battery. These are connected by a dual sensing VSR. The alternator (I believe 40A) charges the engine battery, which engages the VSR and then charges the domestic. I have some solar connected to the domestic.

I want to get a good mains charger for marinas/winter on shore. Ideally something I can leave connected. I see many of the chargers have a minimum and maximum Ah. Ideally I want to get a charger that works for my current set up, and also for future plans to double the capacity domestic by adding another of the same batteries in parallel. If I connect the mains charger to the domestic battery, it currently starts charging 80Ah, which then becomes 150Ah once the VSR engages. (In the future this would be 160Ah, going up to 230Ah).

I have been looking at the Victron Blue Smart IP65 12/25. The datasheet mentions a minimum Ah of 80 (however the manual states 83Ah) and 250Ah as a maximum so it seems to be within the range of my current set up and future plans. (The advantage being I can also take it home, and use it as a 12v power supply to test equipment there.) However, my domestic battery datasheet mentions a maximum charge current of 24A.

Is this a suitable charger for my current and intended future set up? I assume the maximum charge current goes up when the VSR engages. Is it an issue that the charger will be charging with 1A over the maximum charging current until the VSR engages at 13.7 volts?

Alternatively, the charger has a low current mode (10A) that I could use until I expand the domestic capacity. I can also use this if I ever charge the batteries separately.

Any guidance would be much appreciated.

Many thanks.

 

[Sandy]

Here is my set up and it works for me. All kit is Victron apart from the VSR, solar panels and alternator.

• Victron Energy Blue Smart IP22 Charger 12V 30A 1 Output;
• Victron SmartSolar MPPT 75/15;
• Victron SmartShunt 500A;
• Victron Smart Battery Sense;
• 3*130 (390) Ah of House AGM batteries;
• 1*70 Ah of engine AGM; and
• 70 Amp alternator.

Solar power keeps the batteries topped up over the winter and I plug in the shore power when I am aboard for light and power tools. I am NOT a fan of keeping shore power connected 24/7.

When the solar panels are generating power I can see their output on the MPPT and the input at shunt; there is usually a difference. That will be the power that the engine AGM is absorbing.

I have gone for all Victron kit as the BlueSense stuff talks to each other via Bluetooth, frustratingly due to the low power Bluetooth kit I need to stand in a specific point on the boat to get a signal from all of the kit on my phone.

Power input from solar and shore power is connected to the house bank. Power from the alternator is connected to the engine AGM the VSR sorts itself out. There is also a emergency override setting on my On/Off switch should the VSR fail (think of it as a both on a 1-BOTH-2 switch).

 

[BabaYaga]

However, my domestic battery datasheet mentions a maximum charge current of 24A.

Is this a suitable charger for my current and intended future set up? I assume the maximum charge current goes up when the VSR engages. Is it an issue that the charger will be charging with 1A over the maximum charging current until the VSR engages at 13.7 volts?

I would not worry too much over that figure.
24 (A) happens to be 30 percent of 80 (Ah), which is often stated as maximum charge rate for AGM. Question is how much more the battery would accept anyway and for how long. You might check this, if you have a ammeter, by running the engine at full revs when the house battery is well discharged. My guess is you would have less than 24 A going in within few minutes.
Under normal circumstances the VSR will close almost instantly and the current into the starter battery after an engine start will be quite low.
My understanding is that the main drawback of having a charger that is over sized in relation to the domestic bank size is that the battery will spend a longer proportion of time at maximum voltage (absorption) compared to a smaller capacity charger, where more of the Ah's would be put back in during the bulk phase.

 

[Tranona]

There is a danger of over thinking this. What you propose is fine to charge your domestic bank and doubling that bank to 160Ah. In fact you really don't need as much as that, I have a 190Ah bank with a 15A charger and never really see more than 10 amps even when SOC is down below 50%. Not sure I would go the IP65 route. More normal to have a permanently wired in IP22. You lose the portability but gain the simplicity of just plug into shorepower, although makes sense to have a dedicated switched circuit for the charger.

 

[PaulRainbow]

There is a danger of over thinking this. What you propose is fine to charge your domestic bank and doubling that bank to 160Ah. In fact you really don't need as much as that, I have a 190Ah bank with a 15A charger and never really see more than 10 amps even when SOC is down below 50%. Not sure I would go the IP65 route. More normal to have a permanently wired in IP22. You lose the portability but gain the simplicity of just plug into shorepower, although makes sense to have a dedicated switched circuit for the charger.

Spot on. I would go for the Bluesmart IP22, 15a or 20a will be fine.

 

[tymonk]

Thank you all.

Found a very good deal for the IP65 and do like the idea of being able to disconnect easily and take it home to be able to power up 12v items there. Space is slightly also at a premium... Thanks again.