How to use an H bridge to drive a linear actuator (Marine Auto-pilot)

Thread Starter

Stuart Morgan

Joined Sep 19, 2015
2
I Have a raymarine spx5 auto-pilot controller. This has a limited output of 5A continuous (@12V). I want to use a different linear actuator that can draw up-to 15A which will cause an issue if used. I am going to use the attached H-Bridge. So that I can connect the output from the Auto-pilot directly to the input of the H bridge, thus the SPX 5 only needs to supply enough current to drive the input of the H bridge. My question is, can I directly wire the Auto-pilot DC output directly to the two inputs. They are marked on the SPX5 +/- but obviously they swap polarity to push/pull the actuator. As both channels would never be on, when pushing the H Gate Channel PA would receive +12V, PB would be @ 0V. When the autopilot controller is pulling PA would receive 0V and PB +12V.

Note I have ordered the HV version of the brige so it can take high voltage inputs instead of the more usual 5V inputs, so am hoping it will be a simple case of hooking up the O/P of the SPX to the Input of the H-Bridge. The Actuator would connect to the M1/M2 terminals and I would wire a fused 15A supply direct to the B+/B- terminals.

Not being terribly gifted electronics wise I thought I would see if my theory is likey to work in practice without causing a $1000 dollar puff of smoke!

Thanks
 

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Alec_t

Joined Sep 17, 2013
12,733
My question is, can I directly wire the Auto-pilot DC output directly to the two inputs.
It's not entirely clear from the Simple-H manual, but it looks to me as though you'd need PWM inputs to get proportional control of a linear actuator, plus enabling logic signals EA, EB for direction control.
 

Thread Starter

Stuart Morgan

Joined Sep 19, 2015
2
Hi I think (but am not able to easily verify) that the auto-pilot controller just turns on the output to move the actuator. There is a heading sensor, so it stops or usually pulls the opposite direction after a slight over-steer. But its possible that the output of the SPx controller is PWM. IN which case the question is the same, if the output of the auto-pilot controller was pulse width modulated, then presumably that would be also ok to use as the input for the H bridge which can accept either PWM or solid DC inputs??
 

debe

Joined Sep 21, 2010
1,292
If you go to http://www.jgtech.com/pdf/spx5WT.pdf theres a full circuit diagrams of the unit & its H bridge. Looking at the circuit of the H bridge is Tr 1,2,3,4 which are IRFZ48NS. These are 55V & rated at 45Amp. It may be possible to beef up the copper tracks to handle the current & glue fined heat sinks to the MOSFETs using Arctic Silver 2 part epoxy.
 
Last edited:

Alec_t

Joined Sep 17, 2013
12,733
if the output of the auto-pilot controller was pulse width modulated, then presumably that would be also ok to use as the input for the H bridge which can accept either PWM or solid DC inputs?
Debe's link above shows the controller does provide a PWM H-bridge drive to the motor. Providing the PWM rate and voltage are within the specs of your external H-bridge I see no obvious reason why it wouldn't be ok. Anyone care to agree/disagree?
 
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