Batrium BMS question

Noob here.. Im looking into getting 32 cells for a 16s2p 48v battery and need a bms that is not fussy and can be relied on without the worry of it flaking out when needed most. From what I have read Batrium seems to fit the bill. My question is about its charging and discharging limits. For all other BMS's, its always clear what their limits are (ie. Daly's 100A,150A, 200A, etc). I can't seem to find any info on Batrium's limits. Is it because current doesnt flow through the BMS itself? (if that makes any sense..) Thanks in advance.

I assume you're looking at the WatchMon4 with the blockmon cell monitors? I considered that option for my build, but decided it was a bit out of my price range. I believe you are correct that no current flows through the Batrium BMS, so the current limits are a function of the relays/contactors you choose, rather than the BMS.

schroederjd said:

I assume you're looking at the WatchMon4 with the blockmon cell monitors? I considered that option for my build, but decided it was a bit out of my price range. I believe you are correct that no current flows through the Batrium BMS, so the current limits are a function of the relays/contactors you choose, rather than the BMS.

Click to expand...

Yea man, that price hurts.. I just don't want to spend on a cheaper bms to only have to buy another and experience downtime. what did you end up going with? Right im looking at the Watchmon4 and the new one called Watchmon Core with the blockmon cell monitors. I got to read more on relays and contactors, im lost with that. Are they required or just a good recommendation to have?

I'm using the Batrium watchmon 4 on 2 16 cell strings. There are no limits to the hardware. No current flows through it. You can set limits on battery charge/discharge and configure a relay to fire.

I'm looking to upgrade and add 2 more strings. The Batrium does that without a hitch. Just need to buy more blockmons.

I have the batrium hooked up to a shunt trip breaker. Works great.

To me the money was worth it. They have a decent knowledge base and they answer email. Also, I'm in it for the long term. If I spread the cost out over the years, it's not much per year.

Also, about the only thing that I dislike is that the main software is Windows. It's nice software, but I use linux. I'd much rather have a browser tool. There evidently is/was some app for the android, but I haven't found it. There is also some effort to make a cloud solution but haven't seen it yet.

lionel1984 said:

Yea man, that price hurts.. I just don't want to spend on a cheaper bms to only have to buy another and experience downtime. what did you end up going with? Right im looking at the Watchmon4 and the new one called Watchmon Core with the blockmon cell monitors. I got to read more on relays and contactors, im lost with that. Are they required or just a good recommendation to have?

Click to expand...

I ended up going with a TinyBMS from Energus. It’s working ok. My setup is similar to the Batrium in that I don’t have any current going through the BMS (I use a 5A SSR to in line with the inverter’s power switch to control the loads, and a 40A SSR on the positive line of the PV panels to control charging).
I think some kind of external relay, contractor, or remote trip circuit breaker is an essential part of a batrium setup. Without something to disconnect the loads and/or charge controller, the BMS isn’t really able to ‘protect’ the cells.

jtvt said:

I'm using the Batrium watchmon 4 on 2 16 cell strings. There are no limits to the hardware. No current flows through it. You can set limits on battery charge/discharge and configure a relay to fire.

I'm looking to upgrade and add 2 more strings. The Batrium does that without a hitch. Just need to buy more blockmons.

I have the batrium hooked up to a shunt trip breaker. Works great.

To me the money was worth it. They have a decent knowledge base and they answer email. Also, I'm in it for the long term. If I spread the cost out over the years, it's not much per year.

Click to expand...

What are you using to disconnect charging? Are you running your setup as common or separate port?

schroederjd said:

I ended up going with a TinyBMS from Energus. It’s working ok. My setup is similar to the Batrium in that I don’t have any current going through the BMS (I use a 5A SSR to in line with the inverter’s power switch to control the loads, and a 40A SSR on the positive line of the PV panels to control charging).
I think some kind of external relay, contractor, or remote trip circuit breaker is an essential part of a batrium setup. Without something to disconnect the loads and/or charge controller, the BMS isn’t really able to ‘protect’ the cells.

Click to expand...

Thanks. Is there a relay brand thats known for reliability or being the best? Also, is there any reason not to buy a relay that has several times more capacity than whats needed just to have an extra buffer?

jtvt said:

Also, about the only thing that I dislike is that the main software is Windows. It's nice software, but I use linux. I'd much rather have a browser tool. There evidently is/was some app for the android, but I haven't found it. There is also some effort to make a cloud solution but haven't seen it yet.

Click to expand...

The android app is here apparently. App store link

jtvt said:

I'm using the Batrium watchmon 4 on 2 16 cell strings. There are no limits to the hardware. No current flows through it. You can set limits on battery charge/discharge and configure a relay to fire.

I'm looking to upgrade and add 2 more strings. The Batrium does that without a hitch. Just need to buy more blockmons.

I have the batrium hooked up to a shunt trip breaker. Works great.

To me the money was worth it. They have a decent knowledge base and they answer email. Also, I'm in it for the long term. If I spread the cost out over the years, it's not much per year.

Click to expand...

Which shunt trip breaker are you using? Thanks!

schroederjd said:

What are you using to disconnect charging? Are you running your setup as common or separate port?

Click to expand...

A shunt trip breaker. There are a couple youtube videos on setting it up such as


The breaker disconnects load and charging. However, it should never fire. This is an off grid application. You may want a contactor solution for a different application. I weighed the pros and cons of using a contactor vs breaker and decided the breaker was the way to go. Other folks may think differently. The batrium will work fine with either.

lionel1984 said:

The android app is here apparently. App store link

Click to expand...

thx. I looked at that before and it seemed inactive. I'll try again.

lionel1984 said:

Thanks. Is there a relay brand thats known for reliability or being the best? Also, is there any reason not to buy a relay that has several times more capacity than whats needed just to have an extra buffer?

Click to expand...

This is where your specific setup will need to dictate the device(s) required for disconnecting loads and charging. As an example, for my 48V bank, the only loads I have are the inverters (nothing else connected to the batteries), and those inverters have on/off switches that specifically turn off the inverter (ie, the switch does not turn off charging). Very little current flows through those switches, so I'm able to use very small solid state relays (Crydom ED10F) to disconnect my loads (by simply switching off the inverter). On the charging side (I have my BMS set up in separate port mode, so it can disconnect loads and charging independently, depending on the fault state), I've got two 40A / 200V SSRs (TE Connectivity SSRDC-200D40), one for each positive main line coming from my two 3s2p PV arrays. The VoC of each array is 120V, with Isc of ~20A, so I've got a good amount of headroom on those relays.

All that said, my setup is fairly unconventional. Most people seem to run in common port mode with a single contactor (or shunt-trip breaker, or really big SSR) switching off both load and charging. This contactor would typically be placed fairly close to the battery main + so that all loads and charging are switched off in a fault state. In that type of setup, you'll need to size the DC contactor appropriately for the maximum amount of current you expect your battery to deliver/receive. In your case (16s2p), you probably want one per battery, allowing you to run smaller contactors.

To your question of 'headroom' on the relays/contactors, the two downsides I can think of to oversizing your contactors are 1) cost, and 2) the amount of current the coil requires to keep the circuit closed. Shunt trip is a nice option, as they don't take any power when the circuit is closed; the down side is that they have to me manually reset, where as a contactor or SSR will automatically reset when the fault clears. Note also that the shunt trip shown in that video is VERY expensive...

If you tell us a bit more about your system setup, it will be easier to help you with a recommendation on disconnection device.

Batrium comes with a relay(solid state relay ssr) built-in the watchmon core and i think 3 more in the expansion board.

lionel1984 said:

Yea man, that price hurts.. I just don't want to spend on a cheaper bms to only have to buy another and experience downtime. what did you end up going with? Right im looking at the Watchmon4 and the new one called Watchmon Core with the blockmon cell monitors. I got to read more on relays and contactors, im lost with that. Are they required or just a good recommendation to have

Click to expand...