BlueNova Battery Boxes wired in parallel?

[LGH]

Hi Guys,


IÂ’m looking for advice on the feasibility of my idea. For the last 5/6 years I have had the following setup in my Amarok. Starter battery is a normal lead acid to which I had a 10mm2 cable running to the load bin. In there I had the cable split and in parallel it went to 2 x national luna battery boxes, each with a with 100Ah Discovery Dry Cell battery, that was charged by the carÂ’s starter battery/alternator. Each battery box powers their own national fridge/freezer and Engel.


A few months ago, I noticed the one battery was on its last legs so I made a new battery box. This battery box has a BlueNova LiFePO4 154Ah battery in it with, a Victron DC to DC Charger 12v 30A and a Victron Smartshunt amongst a few other things.
Now the problem is IÂ’ve noticed my 2nd Discovery battery is going.
My questions :
- If I create another BlueNova Battery box with SmartShunt do I need to add a 2nd Victron DC to DC charger for that battery box?
So basically, I would have 2 x BlueNova battery boxes each with their own Victron DC to DC chargers and they would be wired in parallel, like my old Discover battery boxes were, to my cars starter battery/alternator.
- Also would my AmarokÂ’s alternator be able handle 2 x BlueNova battery boxes, each with their own DC to DC charger?

Thanks

[Fluffy]

I'm thinking about this.

[heyyahhey]

I'm thinking about this.

I built a box that houses two BN 104ah batteries. Both batteries are wired to positive and negative bus bars, and the charge feeds also come to these bus bars.

Chargers are:
NL 25a DCDC
Victron MPPT 20/100
Victron AC charger

Plus BM712 BT monitor/shunt.

i did this because I have fixed solar on the RTT so with this setup I can use the NL to charge from alternator and the victron to simultaneously charge with solar. When camped, I have some flexible
panels that I plug into the NL charger MPPT port.

With this setup, batteries both discharge and charge relatively evenly. If 1 reaches 100% soc first, all the amps go to the other. We are usually back to full SOC within 2-3 hours depending on the depth of discharge.

I’ve had no issues with either charger “backing off” due to voltage or amps provided by the other charger.

i took care to make the leads for each battery to the bus bars the same length, which I think is important for keeping them balanced. I installed battery switches externally in addition to internal 100a circuit breakers (blue sea systems) so I can easily isolate one or the other battery.

the challenge with your setup would imho be the unequal lead length which would probably result in the battery with shorter leads charging and discharging a bit faster, but, I’d not think this is a huge deal considering the individual batteries have BMS. I would think you could use the larger 100a BH plug to connect one box to the other. Or
maybe even the regular (rated to 50a) would work. I’d go larger if you plan to use a larger inverter and pull from both batteries.

As far as alternator - I think it depends on the output rating of the alternator - I know that the 40a NL dcdc in my caravan can pose a challenge to the alternator on my disco if at idle. With some revs it’s fine

[bigboy529]

I built a box that houses two BN 104ah batteries. Both batteries are wired to positive and negative bus bars, and the charge feeds also come to these bus bars.

Chargers are:
NL 25a DCDC
Victron MPPT
Vixtron AC charger

i did this because I have fixed solar on the RTT so with this setup I can use the NL to charge from alternator and the victron to simultaneously charge with solar. When camped, I have some flexible
panels that I plug into the NL charger MPPT port.

With this setup, batteries both discharge and charge relatively evenly. If 1 reaches 100% soc first, all the amps go to the other.

I’ve had no issues with either charger “backing off” due to voltage or amps provided by the other charger.

i took care to make the leads for each battery to the bus bars the same length, which I think is important for keeping them balanced. I installed battery switches externally in addition to internal 100a circuit breakers (blue sea systems) so I can easily isolate one or the other battery.

the challenge with your setup would imho be the unequal lead length which would probably result in the battery with shorter leads charging and discharging a bit faster, but, I’d not think this is a huge deal considering the individual batteries have BMS.

As far as alternator - I think it depends on the output rating of the alternator - I know that the 40a NL dcdc in my caravan can pose a challenge to the alternator on my disco if at idle. With some revs it’s fine

This is how I would personally do it as well.
Having 2x DC-DC, 2x Smart Shunts etc. in the system will be total overkill.
The 30A Victron DC-DC you already have, will be big enough to charge 2x 150Ah batteries in parallel and you can connect them in parallel via the one Smart Shunt as well.

A left field suggestion would be to not even add a second battery, a 150Ah lithium is big enough for the 2 fridges. I understand why guys opted for a dedicated battery for each fridge in the lead acid days, but with lithium these days it is no longer needed.

Depending on how much you drive on your trips, your money might be better spent on adding a MPPT solar controller and 100 to 200W of solar to your setup.

It's hard to say with alternators, remember the 2x 30A DC-DC chargers will be drawing slightly more than 60A while bulk charging, (yes the Victron DC-DC can actually goes slightly over its rated output).

[heyyahhey]

This is how I would personally do it as well.
Having 2x DC-DC, 2x Smart Shunts etc. in the system will be total overkill.
The 30A Victron DC-DC you already have, will be big enough to charge 2x 150Ah batteries in parallel.

A left field suggestion would be to not even add a second battery, a 150Ah lithium is big enough for the 2 fridges. I understand why guys opted for a dedicated battery for each fridge in the lead acid days, but with lithium these days it is no longer needed.

Depending on how much you drive on your trips, your money would be better spent on adding a MPPT solar controller and 100 to 200W of solar to your setup.

Agree RE 150a. We run two fridges, two CPAPs at night, and sometimes even electric blankets and we usually have 40% on tap in the morning with 200a,
which allows us to run the nespresso machine on the inverter in the morning.

[LGH]

I built a box that houses two BN 104ah batteries. Both batteries are wired to positive and negative bus bars, and the charge feeds also come to these bus bars.

Chargers are:
NL 25a DCDC
Victron MPPT 20/100
Victron AC charger

Plus BM712 BT monitor/shunt.

i did this because I have fixed solar on the RTT so with this setup I can use the NL to charge from alternator and the victron to simultaneously charge with solar. When camped, I have some flexible
panels that I plug into the NL charger MPPT port.

With this setup, batteries both discharge and charge relatively evenly. If 1 reaches 100% soc first, all the amps go to the other. We are usually back to full SOC within 2-3 hours depending on the depth of discharge.

I’ve had no issues with either charger “backing off” due to voltage or amps provided by the other charger.

i took care to make the leads for each battery to the bus bars the same length, which I think is important for keeping them balanced. I installed battery switches externally in addition to internal 100a circuit breakers (blue sea systems) so I can easily isolate one or the other battery.

the challenge with your setup would imho be the unequal lead length which would probably result in the battery with shorter leads charging and discharging a bit faster, but, I’d not think this is a huge deal considering the individual batteries have BMS. I would think you could use the larger 100a BH plug to connect one box to the other. Or
maybe even the regular (rated to 50a) would work. I’d go larger if you plan to use a larger inverter and pull from both batteries.

As far as alternator - I think it depends on the output rating of the alternator - I know that the 40a NL dcdc in my caravan can pose a challenge to the alternator on my disco if at idle. With some revs it’s fine

Good Morning,
Thank you so much for your reply.

Your idea is great and as you said the problem I'm going to have, using your suggestion, will definitely be the lead lengths being very different. Maybe if I were use 125A BH connectors between the battery boxes, with 25mm2 wire that might help. On the second box I would install an external battery switch and inside just next to the positive terminal I would install an ANL fuse folder with a 100/125A ANL fuse or maybe I could try your suggestion of a 100A circuit breaker.

So with your suggestion, if I'm thinking it through correctly, the 2nd battery box is purely a store for a battery and its purpose would be to double my available Amp Hours of the system. I wouldn't connect any loads there, because I would want all my loads on the first battery box on the load side of the Victron SmartShunt.
The downside I see is that the second battery could never be used on its own.

Am I correct?

[LGH]

This is how I would personally do it as well.
Having 2x DC-DC, 2x Smart Shunts etc. in the system will be total overkill.
The 30A Victron DC-DC you already have, will be big enough to charge 2x 150Ah batteries in parallel and you can connect them in parallel via the one Smart Shunt as well.

A left field suggestion would be to not even add a second battery, a 150Ah lithium is big enough for the 2 fridges. I understand why guys opted for a dedicated battery for each fridge in the lead acid days, but with lithium these days it is no longer needed.

Depending on how much you drive on your trips, your money might be better spent on adding a MPPT solar controller and 100 to 200W of solar to your setup.

It's hard to say with alternators, remember the 2x 30A DC-DC chargers will be drawing slightly more than 60A while bulk charging, (yes the Victron DC-DC can actually goes slightly over its rated output).

Good Morning,

Thanks for your reply, do you think it's possible to split the output side of the Victron DC to DC charger with 2 x BH connectors?
Then I could have 2 separate battery boxes that I could move as/if needed when charged.
The biggest problem I see here though would be the different SOC's of the 2 battery boxes and I don't think the DC to DC charger would handle that without causing issues.
So, I think then the 2 batteries have to be connected in parallel as discussed in a previous post.
The only way I can see for them to work as two separate batteries, if needed, is to duplicate the DC to DC chargers. which is expensive. Maybe a smaller 18A Victron DC to DC charger on the 2nd battery but that would still be close to 50 Amps and that would I'm sure put a strain on my Amarok alternator.

I haven't yet used my battery box with the BlueNova Lithium, so I think maybe I should do as you said and try powering both fridges of it before I go spend money on another battery etc.

Thanks

[heyyahhey]

Good Morning,
Thank you so much for your reply.

Your idea is great and as you said the problem I'm going to have, using your suggestion, will definitely be the lead lengths being very different. Maybe if I were use 125A BH connectors between the battery boxes, with 25mm2 wire that might help. On the second box I would install an external battery switch and inside just next to the positive terminal I would install an ANL fuse folder with a 100/125A ANL fuse or maybe I could try your suggestion of a 100A circuit breaker.

So with your suggestion, if I'm thinking it through correctly, the 2nd battery box is purely a store for a battery and its purpose would be to double my available Amp Hours of the system. I wouldn't connect any loads there, because I would want all my loads on the first battery box on the load side of the Victron SmartShunt.
The downside I see is that the second battery could never be used on its own.

Am I correct?

Yes, the 2nd battery would just be additional amp hour capacity - and you could use the system with or without it. The way I built mine, I can run it with either just one, or both, batteries in the box. That second battery does double duty in my caravan - so I swap it back and forth.
Thi
s is what I used as a circuit breaker, installed just down from the positive terminals:

https://www.amazon.com/Blue-Sea-Syst...323516&sr=8-10

I selected a 100a breaker because that's also the max continuous draw on the BN 104 battery - your rating may be higher on that larger battery, though short of running a big inverter, you would certainly never need that capacity, and then there is the wire sizing to consider, etc.

[bigboy529]

Good Morning,

Thanks for your reply, do you think it's possible to split the output side of the Victron DC to DC charger with 2 x BH connectors?
Then I could have 2 separate battery boxes that I could move as/if needed when charged.
The biggest problem I see here though would be the different SOC's of the 2 battery boxes and I don't think the DC to DC charger would handle that without causing issues.
So, I think then the 2 batteries have to be connected in parallel as discussed in a previous post.
The only way I can see for them to work as two separate batteries, if needed, is to duplicate the DC to DC chargers. which is expensive. Maybe a smaller 18A Victron DC to DC charger on the 2nd battery but that would still be close to 50 Amps and that would I'm sure put a strain on my Amarok alternator.

I haven't yet used my battery box with the BlueNova Lithium, so I think maybe I should do as you said and try powering both fridges of it before I go spend money on another battery etc.

Thanks

The 2 different SOC levels will confuse the charge stages of the DC-DC charger,though this shouldn't really be a issue I'd say unless there is a big difference in SOC on a regular bases, something like 30% and 80% for the other.

If you want to go with the 2 batteries and want to be able to take one out if needed or have one as backup in case the other one goes broken in the middle of the bush, then I would do it with bus bars.
1. Connect the 10mm2 cables running from your starting battery to the input of the Victron DC-DC charger.
2. Connect the output of the Victron DC-DC to a positive and negative busbar, like this, not necessarily this one, it's just the first Google result I got. https://www.livestainable.co.za/prod...xoCjFoQAvD_BwE
3. Then connect each battery box indavidually to the same busbars, so a positive and negative from each battery box. For convenience you can do this with connectors, Brad Haris connectors will work well. If you want you can add disconnect switches/breakers for each battery as well, as already suggested.
4. If you add a solar controller in future, you would then connect the output of the solar controller to the same busbars, the solar will then also charge both batteries if they are connected to the busbars.

With that being said, if I were you I'd really try get bye with only one battery first, 150Ah of lithium capacity is plenty for 2 fridges, some LED lights at night, maybe charging a device here and there.

[LGH]

Yes, the 2nd battery would just be additional amp hour capacity - and you could use the system with or without it. The way I built mine, I can run it with either just one, or both, batteries in the box. That second battery does double duty in my caravan - so I swap it back and forth.
Thi
s is what I used as a circuit breaker, installed just down from the positive terminals:

https://www.amazon.com/Blue-Sea-Syst...323516&sr=8-10

I selected a 100a breaker because that's also the max continuous draw on the BN 104 battery - your rating may be higher on that larger battery, though short of running a big inverter, you would certainly never need that capacity, and then there is the wire sizing to consider, etc.

The leads to the 2nd battery would be about 1m in length, more then double the length of the first battery boxes lead length. I would make them out of 25mm2 wire. Do you think that would be ok for the balancing on the DC to DC Charger?

[heyyahhey]

The leads to the 2nd battery would be about 1m in length, more then double the length of the first battery boxes lead length. I would make them out of 25mm2 wire. Do you think that would be ok for the balancing on the DC to DC Charger?

I certainly think so - I think you'd see a small percentage difference in amps (both in charging and discharging), which would increase depending on the extent to which you discharge, but the BMSs in the individual batteries are going to limit current as they get near full anyways, so the result is just that the lower of the two batteries gets more, and eventually all, current.

I have never used cable that big - I use 16mm2 for the battery leads - the runs are very short, as you mention. You will end up with some big connectors and akwardness, IMHO, at 25mm2

Now, if your primary battery connections are 16mm2 - and the leads to the second are 25mm2 - I lack the math and formula skills to figure out whether that would eliminate any difference - I would think it would only reduce the delta - but there are much wiser electrikery peeps around on here who would answer that better.

[Fluffy]

I built a box that houses two BN 104ah batteries. Both batteries are wired to positive and negative bus bars, and the charge feeds also come to these bus bars.

Chargers are:
NL 25a DCDC
Victron MPPT 20/100
Victron AC charger

Plus BM712 BT monitor/shunt.

i did this because I have fixed solar on the RTT so with this setup I can use the NL to charge from alternator and the victron to simultaneously charge with solar. When camped, I have some flexible
panels that I plug into the NL charger MPPT port.

With this setup, batteries both discharge and charge relatively evenly. If 1 reaches 100% soc first, all the amps go to the other. We are usually back to full SOC within 2-3 hours depending on the depth of discharge.

I’ve had no issues with either charger “backing off” due to voltage or amps provided by the other charger.

i took care to make the leads for each battery to the bus bars the same length, which I think is important for keeping them balanced. I installed battery switches externally in addition to internal 100a circuit breakers (blue sea systems) so I can easily isolate one or the other battery.

the challenge with your setup would imho be the unequal lead length which would probably result in the battery with shorter leads charging and discharging a bit faster, but, I’d not think this is a huge deal considering the individual batteries have BMS. I would think you could use the larger 100a BH plug to connect one box to the other. Or
maybe even the regular (rated to 50a) would work. I’d go larger if you plan to use a larger inverter and pull from both batteries.

As far as alternator - I think it depends on the output rating of the alternator - I know that the 40a NL dcdc in my caravan can pose a challenge to the alternator on my disco if at idle. With some revs it’s fine

Nope, that the stuff of urgan legends.

Remember what you said about one battery at 100% AND THE OTHER THEN CATCHING UP . THIS HAPPENS ALL THE TIME WITH A lithium BATTERY DUAL SETUP, EVEN AT 50% soc. THE INTERNAL bms WILL ENSURE THAT YOU DON'T LAND UP DERIOUSLY UNBALANCED.

Unlike Lead acids in parallel where one battery is charging at 40A and the other at 4A. Lithium's have an internal charge rate control mechanism.

[heyyahhey]

Nope, that the stuff of urgan legends.

Remember what you said about one battery at 100% AND THE OTHER THEN CATCHING UP . THIS HAPPENS ALL THE TIME WITH A lithium BATTERY DUAL SETUP, EVEN AT 50% soc. THE INTERNAL bms WILL ENSURE THAT YOU DON'T LAND UP DERIOUSLY UNBALANCED.

Unlike Lead acids in parallel where one battery is charging at 40A and the other at 4A. Lithium's have an internal charge rate control mechanism.

Makes sense —- what I meant really was charge discharge at the same rate. The BMS certainly gets them balanced at the end. When I have the two Lithiums in the caravan, the one on the left side (they go behind each wheel well) has about .5m more cable x 2, and there is definitely a difference in charge and discharge rates from that battery. But the one with shorter cables gets full and the power all goes to the other, and it catches up quick…