BigBattery 170 Concerns

[syspig]

Fair warning - limited knowledge ahead.

DIY is not for me. So, like many, I'm on the fence between going with a known quantity/quality (Battle Born or Lifeblue) and paying the premium, or taking a bit of a gamble on a newer company and saving money (BigBattery.) I can work through most of that comfort level on my own, but I've concerns - perhaps unfounded - on the BigBattery 170ah 12v design.

First up - the power switch. I'm not seeing the upside in multi-battery installations, especially in the two projects I'm working on (travel trailer 2x170ah, van with 4x170ah, parallel 12v for both). Both installations will require a couple minutes to access the battery banks, so even if I wanted to power them on/off from the integrated battery switch, that would be inconvenient. Having the bank/batteries always "live" with an external disconnect switch is easy. For that matter, given they won't be visible - the voltage display isn't of much use either and while likely minimal, it's just a power drain in my case.

Perhaps the answer to the above is to just leave them on, and still use an external disconnect switch - but my concern there is what happens in the event of a switch failure on one of the batteries, or inadvertent powering off of one or more batteries in the bank. Should that happen, I've now got an unexpected reduction in battery bank capacity and mismatched charge level once the situation is addressed. If this concern is valid, any reason the power switch couldn't be bypassed? Or, does the BMS use it to shut things down when a temperature/voltage situation requires that?

Second up - the Anderson connector. At the rated 175A draw, it looks like one is fine with 4AWG for short feed connectors to a bus bar. However, the battery specs show a max peak current of 350A - this bumps it up to 2/0 on the wire sizing calculator I use (Blue Seas). I do see there's a SB175 connector that handles 2/0, but BigBattery only appears to be selling SB175 connectors with 6AWG wires, and I'm seeing posts here of many folks using them. I must be missing something basic here...how can one safely use feed connectors this small with the rated continuous output of this battery?

Lastly, assuming the wire gauge issue is addressed - the location of the Anderson connector on the battery seems far from ideal. If one wants all the battery switches/displays facing the same direction - a must, in my layouts - this makes for incredibly inefficient layout options. In looking at the video posted by @Will Prowse, the feed cable will have the Anderson connector and cable sticking out quite a bit - an amount that essentially increases the battery width when placing them side by side. That's a shame, as layout options would seem far more flexible and compact if the feeds went into the top. Does anyone have any tips for keeping a bank of 4-6 of these batteries compact?

Again, not knocking the BigBattery intentionally - I want to like them, and want to purchase them if the above concerns can be addressed. Thanks in advance for any education received.

 

[syspig]

Bumping in hopes of a followup. I've tried emailing BigBattery as well, but no response from them as of yet.

I've addressed all my concerns above except the wiring question, specifically if the specialized SB175 connector with 2/0 wire is needed given the battery specs list a max draw of 350a over 6 seconds. To be clear, as the basics of my system show below, I can't envision any possible way that could happen - but that's why I'm inquiring with the experts.

Plans are to take four 175ah to a bus bar (estimating 24" leads on each), then size the wire accordingly from the bus bar to the Victron 3000VA Multiplus Inverter/charger. So, as I understand things - in normal operation, each of the Anderson SB175 leads would carry 25% of the total load.

When considering something unexpected - I'm having trouble envisioning any scenario that would result in a load from a single battery approaching the limits of 1/0 cable in a standard Anderson SB175 connector. It would seem the inverter would need to be maxed out, additional heavy DC loads would need to be present, AND three of the four 175ah batteries would somehow be powered off/offline.

Thoughts/advice? Is any more info needed?

 

[villagepowerdesign]

Hey syspig - so I have had the same concerns - I'm a career solar engineer - 40 years - so can provide some insight. First switches don't tend to fail but they do tend to get accidentally switched off - but I'm planning on just mounting so that can't happen - not a major concern. But as for cable size - Yes as a licensed electrician I'm amazed that all the battery companies use such skimpy cable sizes. It's the age-old interface between electronics folks and power folks - sure you can get by with cranking 200 amps through two 200ºC insulation rated 6 AWGs for short periods for a few inches but to supply 6 AWG output cables on a battery that's supposed to be 175 Amps continuous to me is outright criminal besides being dangerous. However you also don't need to go to 2/0 if you get quality 90ºC or better UL cable. I won't go into the fullness of how to calculate temp derates from NEC table 310.15(b)(16) but suffice it to say that if you are paralleling batteries you can figure the max amps your inverter or other loads will draw from the whole pack - divide that by how many paralleled batteries you have so you are looking at the max amperage each battery will see in your setup. So if you have a 2 KW inverter on 2 BB 170s at 12 volts - the total inverter amperage is on the order of 165 Amps but if you have two batteries in parallel each one will only see 83 Amps max. So the parallel cables can get by with like 2 AWG cables (in my book - still NOT 6 AWG) and the final pack cable set should be at least 1/0 (which does fit in the 175 A Anderson connector). Hope that helps!

 

[villagepowerdesign]

And I was speaking for distances below like 10' - you have to consult a voltage drop calculator and I recommend staying below 3% volt drop on all cables. but for most van setups you are closer than 10' if you keep the batteries and inverter close. So it depends on your total inverter and DC loads - but I would recommend 1/0 for up to 170 Amps, 2/0 for up to 225 Amps and 4/0 for anything over that. For parallel cables - 2 AWG for up to 90 Amps, 1 AWG for up to 130 Amps

 

[syspig]

Thanks much!

...but suffice it to say that if you are paralleling batteries you can figure the max amps your inverter or other loads will draw from the whole pack - divide that by how many paralleled batteries you have so you are looking at the max amperage each battery will see in your setup. So if you have a 2 KW inverter on 2 BB 170s at 12 volts - the total inverter amperage is on the order of 165 Amps but if you have two batteries in parallel each one will only see 83 Amps max.

With four 170ah batteries and a 3 KW inverter, it seems like I have plenty of headroom with the standard SB175 connector and wire smaller than 2/0. There will be DC loads in addition to the inverter, of course - but they will be relatively minimal. Lights, water pump, heater motor - typical RV components that are low draw.

My installer doesn't like taking any chances, though. Especially since they're aware I've talked about moving batteries around between van, trailer and anything else that may need them down the road. The Anderson connectors make that an especially appealing option, but if I remove one or more from the van bank of four - that load overhead gets much smaller.

Given we're only talking about four pairs of feed wires with the SB175's, each of which will likely be 24" in length or less - my gut's telling me to go 2/0, even though it's likely total overkill. That's a minimal incremental cost in the big picture of this install and gives peace of mind.

Thanks again for your input!

 

[villagepowerdesign]

Yes assuming you are at 12 volts then your inverter will draw a max of 250 Amps - so parallel cables will only see 1/3 of that so at 85 Amps or 2 AWG BUT the final output wires from the pack to the Main DC disco and from the Disco to the inverter will definitely have to be 2/0 at minimum 4/0 recommended - especially if more than a few feet long.

 

[EricBarbour]

With four 170ah batteries and a 3 KW inverter, it seems like I have plenty of headroom with the standard SB175 connector and wire smaller than 2/0. There will be DC loads in addition to the inverter, of course - but they will be relatively minimal. Lights, water pump, heater motor - typical RV components that are low draw.

Then why are you worried about a 250-amp load? Fuse the output of the battery for the maximum EXPECTED load.

BigBattery's Anderson cables are "only" 6 AWG, but they are made of silicone-covered wire able to handle a lot of heat. I have four of their 100AH 2170 battery packs and use their cables to interconnect them. I'm on a 48v system and don't ever expect to pull more than 60-70 amps, and then only for brief periods.

My installer doesn't like taking any chances, though. Especially since they're aware I've talked about moving batteries around between van, trailer and anything else that may need them down the road. The Anderson connectors make that an especially appealing option, but if I remove one or more from the van bank of four - that load overhead gets much smaller.

So why isn't the installer offering to make custom cables for you?

 

[villagepowerdesign]

Just cause they can handle the heat why throw away power? I would never consider using 6 AWG wire for anything over 80 amps just from a voltage drop and power loss perspective. Use a basic voltage drop calculator. In the PV industry we seldom let any PV inputs fall below 1.5% drop - I consider 3% to be max for battery cables. 200 Amps at 12V at 4 feet on 6 AWG is a 6.55% voltage drop or a wasted 157 Watts. Invest in wire now and save many years of Amphours over the lifetime. What I also worry about is someone using regular 60ºC or 90ºC wire or battery cable and thinking they can get by with 6 AWG = Fire!

 

[Dzl]

One more variable to add to the conversation, if you size the wire based on each battery handling only its share of the load 1/4, 1/3, 1/2 etc, what happens if a BMS or some other factor takes a pack offline. It seems like you want to design for some amount of fault tolerance / redundancy unless these BMSes coordinate with eachother? At the very least I would want enough overhead that the bank could safely carry the full load if one battery was taken offline.

I also agree with @villagepowerdesign just because a wire can carry a load does not mean it should. A small wire with high temp rating can carry higher current, but there will be higher voltage drop, higher power loss, and more energy wasted as heat. Voltage drop in the battery cables affects every circuit down/up stream of it. And even at 200*C insulation rating 6AWG is only rated for max of 135A according to the ABYC chart I referenced (not sure how NEC would differ, usually they are fairly similar).

One last point, you should be aware that the Victron Multiplus 3000, has a surge capability of 6000W for up to 2 minutes. With cheap HF inverters you usually don't have to account for surge in wire sizing since its only a few dozen milliseconds usually, but with a LF inverter where surge could be minutes, I would think it might be more important to consider. What are your thoughts?

 

[JAS]

To add to this discussion...

I really wanted to like this battery too... (Aside from the initial low temp disconnect problem). However, I want to use the battery in a more mobile solution (ie: carrying back and forth from home to my cabin). At first glance, the Anderson connector and power switch implies doing this easier. However, my problem (in another thread) is how do I keep track of the state of charge (without modding the case and voiding the warranty)?

In addition, I've also contacted (or tried) BB via email/online web form/facebook multiple times and only received one response from someone who clearly didn't know what they were talking about. All other attempts (including my response to that one contact) have gone unanswered...

So in summary, I'm not buying their product...

 

[Dzl]

To add to this discussion...

I really wanted to like this battery too... (Aside from the initial low temp disconnect problem). However, I want to use the battery in a more mobile solution (ie: carrying back and forth from home to my cabin). At first glance, the Anderson connector and power switch implies doing this easier. However, my problem (in another thread) is how do I keep track of the state of charge (without modding the case and voiding the warranty)?

Have you found any battery that meets your needs in this regard?

It seems like a portable power station / 'solar generator' might be a better match for a plug and play system that meets your needs if you don't want to add additional components into the mix.

 

[JAS]

Have you found any battery that meets your needs in this regard?

Indeed, I was eyeing Jackery or Bluetti. But, I just couldn't swallow spending the money on those when I could build one for about the same price that will have many more charging cycles and I can swap out components as needed.

So I built a "portable solar generator" in a Rigid ToolBox with a BattleBorn 100AH 12V that I've been lugging back and forth. It's not exactly portable... Probably weighs 50-55 lbs and is bulky.

Therefore, I'm still looking for a more permanent type setup to leave at the cabin. I also would like more AH than just the one BattleBorn that I have. So I was thinking of the BigBattery (with another CC and Inverter) at the cabin. And if concerned, I could just haul the battery back and forth. (Concerned about very low temps in the winter and/or theft).

So to answer your question... I'm leaning towards the 200AH SOK Battery with an AiLi Battery Monitor.

 

[MrNatural22]

To add to this discussion...

I really wanted to like this battery too... (Aside from the initial low temp disconnect problem). However, I want to use the battery in a more mobile solution (ie: carrying back and forth from home to my cabin). At first glance, the Anderson connector and power switch implies doing this easier. However, my problem (in another thread) is how do I keep track of the state of charge (without modding the case and voiding the warranty)?

In addition, I've also contacted (or tried) BB via email/online web form/facebook multiple times and only received one response from someone who clearly didn't know what they were talking about. All other attempts (including my response to that one contact) have gone unanswered...

So in summary, I'm not buying their product...

As far as monitoring the battery I’m thinking if you use a $40 aili coulumb battery meter with the shunt connected thru your neg battery cable and on the outside of the case and mounted to the top of the box this would allow you to monitor your battery. Should be a simple install? I used a automotive single gauge pod as a clean way to mount the meter.
This all would be outside of the batteries case and you would not have to open or alter the case.
?

 

[JAS]

This all would be outside of the batteries case and you would not have to open or alter the case.

Mr. Natural,

Yes, I had thought of doing just that. (The autopod is a great option. I hadn't thought of that and makes it a neater option). But, then I'm back to a cabling conundrum... From the Anderson connector to some sort of frankenstein cable and then back to an Anderson connector (if I want to keep it quick connect/disconnect). Still seems like a lot of junk hanging out the back of the battery. At least with the SOK (or any standard style battery), I can have just 2 short cables running into an Anderson connector (with the shunt connected directly to the terminal) that isn't hanging too far out. Note: I've discovered that on the AiLi, the Shunt has all the brains... IE: the meter can be disconnected from the shunt without losing the state of charge

However, more importantly, I'm pretty sure turning off the power switch on the Big Battery (either intentionally or accidentally) would reset the meter. In order for the meter not to get reset, the shunt would have to be installed before the kill switch. (correct me if I'm wrong?)

Thanks,

Jeff

 

[Ampster]

how can one safely use feed connectors this small with the rated continuous output of this battery?

The load is what should determine the current. My pack is capable of discharging over 600 Amps but I never expect to draw more than 100 Amps. I have a 125 Amp fuse to protect the #2 wire.

 

[syspig]

Yes assuming you are at 12 volts then your inverter will draw a max of 250 Amps

Per the vendor I'm buying the Victron goods from, AMSolar - the inverter can burst to 400 amps. For how long, and how that impacts the wiring decision - I don't know.

 

[syspig]

So why isn't the installer offering to make custom cables for you?

They are, and they've got a nice 16 ton hydraulic crimper to do it right with whatever we end up with.

However, they've never used Anderson connectors - just traditional lugs. Typically, they just do most battery to bus bar feeds with 2/0 and call it a day - sizing the main busbar feed as appropriate.

 

[syspig]

To add to this discussion...

I really wanted to like this battery too... (Aside from the initial low temp disconnect problem). However, I want to use the battery in a more mobile solution (ie: carrying back and forth from home to my cabin). At first glance, the Anderson connector and power switch implies doing this easier. However, my problem (in another thread) is how do I keep track of the state of charge (without modding the case and voiding the warranty)?

In addition, I've also contacted (or tried) BB via email/online web form/facebook multiple times and only received one response from someone who clearly didn't know what they were talking about. All other attempts (including my response to that one contact) have gone unanswered...

So in summary, I'm not buying their product...

RE moving the batteries around - that's a key part of my design. I've got a setup in both van and travel trailer, and depending on what is being used - the pack size will be flexible in either. Most of the time, it will be 4x170 in the van, and 2x170 in the travel trailer - but the van will be built out to support 6x170, and the trailer to support 3x170.

I have learned enough from reading here and listening to those more knowledgeable, that simply tossing batteries back and forth ignoring SOC is dumb. However, that's where I'm hoping these particular batteries will help out quite a bit. Not only with the Anderson connector (those could be added to anything), but with the individual on/off switches. As mentioned my original post, I couldn't see a need for that - but unless I'm missing something, I now I think they'll be great for dealing with SOC.

For example, if I'm taking only the van and want it filled to the gills with all six batteries - I'll top off the bank of four that are already in there, then power them off via their individual switches. Plug in the two from the trailer, top them off, then everything can be powered up at the same SOC.

 

[rboothe]

And I was speaking for distances below like 10' - you have to consult a voltage drop calculator and I recommend staying below 3% volt drop on all cables. but for most van setups you are closer than 10' if you keep the batteries and inverter close. So it depends on your total inverter and DC loads - but I would recommend 1/0 for up to 170 Amps, 2/0 for up to 225 Amps and 4/0 for anything over that. For parallel cables - 2 AWG for up to 90 Amps, 1 AWG for up to 130 Amps

This is really helpful. I'm having a very tough time figuring out the actual amp draw of my battery bank (I have a standard camper van setup with a solar charge controller, inverter, etc). I have two 205aH 12V batteries wired in parallel for a 4920watt system. I also have a 2500watt inverter. I'm really having trouble figuring out the wire size from battery to battery and from battery bank to inverter. I guess I'm just not understanding the amperage going through the wire. I would love any advice or help you have.

 

[Ampster]

You could start out with 2500 Watts, divided by 12 volts gets you 208 Amps. Size the wire and fuses for that unless you are sure you are not going to use all that inverter capacity.